// This contract is part of Zellic’s smart contract dataset, which is a collection of publicly available contract code gathered as of March 2023. // SPDX-License-Identifier: MIT pragma solidity ^0.8.4; /** **************************************************************************** * @notice Interface for contracts using VRF randomness * ***************************************************************************** * @dev PURPOSE * * @dev Reggie the Random Oracle (not his real job) wants to provide randomness * @dev to Vera the verifier in such a way that Vera can be sure he's not * @dev making his output up to suit himself. Reggie provides Vera a public key * @dev to which he knows the secret key. Each time Vera provides a seed to * @dev Reggie, he gives back a value which is computed completely * @dev deterministically from the seed and the secret key. * * @dev Reggie provides a proof by which Vera can verify that the output was * @dev correctly computed once Reggie tells it to her, but without that proof, * @dev the output is indistinguishable to her from a uniform random sample * @dev from the output space. * * @dev The purpose of this contract is to make it easy for unrelated contracts * @dev to talk to Vera the verifier about the work Reggie is doing, to provide * @dev simple access to a verifiable source of randomness. It ensures 2 things: * @dev 1. The fulfillment came from the VRFCoordinator * @dev 2. The consumer contract implements fulfillRandomWords. * ***************************************************************************** * @dev USAGE * * @dev Calling contracts must inherit from VRFConsumerBase, and can * @dev initialize VRFConsumerBase's attributes in their constructor as * @dev shown: * * @dev contract VRFConsumer { * @dev constructor(, address _vrfCoordinator, address _link) * @dev VRFConsumerBase(_vrfCoordinator) public { * @dev * @dev } * @dev } * * @dev The oracle will have given you an ID for the VRF keypair they have * @dev committed to (let's call it keyHash). Create subscription, fund it * @dev and your consumer contract as a consumer of it (see VRFCoordinatorInterface * @dev subscription management functions). * @dev Call requestRandomWords(keyHash, subId, minimumRequestConfirmations, * @dev callbackGasLimit, numWords), * @dev see (VRFCoordinatorInterface for a description of the arguments). * * @dev Once the VRFCoordinator has received and validated the oracle's response * @dev to your request, it will call your contract's fulfillRandomWords method. * * @dev The randomness argument to fulfillRandomWords is a set of random words * @dev generated from your requestId and the blockHash of the request. * * @dev If your contract could have concurrent requests open, you can use the * @dev requestId returned from requestRandomWords to track which response is associated * @dev with which randomness request. * @dev See "SECURITY CONSIDERATIONS" for principles to keep in mind, * @dev if your contract could have multiple requests in flight simultaneously. * * @dev Colliding `requestId`s are cryptographically impossible as long as seeds * @dev differ. * * ***************************************************************************** * @dev SECURITY CONSIDERATIONS * * @dev A method with the ability to call your fulfillRandomness method directly * @dev could spoof a VRF response with any random value, so it's critical that * @dev it cannot be directly called by anything other than this base contract * @dev (specifically, by the VRFConsumerBase.rawFulfillRandomness method). * * @dev For your users to trust that your contract's random behavior is free * @dev from malicious interference, it's best if you can write it so that all * @dev behaviors implied by a VRF response are executed *during* your * @dev fulfillRandomness method. If your contract must store the response (or * @dev anything derived from it) and use it later, you must ensure that any * @dev user-significant behavior which depends on that stored value cannot be * @dev manipulated by a subsequent VRF request. * * @dev Similarly, both miners and the VRF oracle itself have some influence * @dev over the order in which VRF responses appear on the blockchain, so if * @dev your contract could have multiple VRF requests in flight simultaneously, * @dev you must ensure that the order in which the VRF responses arrive cannot * @dev be used to manipulate your contract's user-significant behavior. * * @dev Since the block hash of the block which contains the requestRandomness * @dev call is mixed into the input to the VRF *last*, a sufficiently powerful * @dev miner could, in principle, fork the blockchain to evict the block * @dev containing the request, forcing the request to be included in a * @dev different block with a different hash, and therefore a different input * @dev to the VRF. However, such an attack would incur a substantial economic * @dev cost. This cost scales with the number of blocks the VRF oracle waits * @dev until it calls responds to a request. It is for this reason that * @dev that you can signal to an oracle you'd like them to wait longer before * @dev responding to the request (however this is not enforced in the contract * @dev and so remains effective only in the case of unmodified oracle software). */ abstract contract VRFConsumerBaseV2 { error OnlyCoordinatorCanFulfill(address have, address want); address private immutable vrfCoordinator; /** * @param _vrfCoordinator address of VRFCoordinator contract */ constructor(address _vrfCoordinator) { vrfCoordinator = _vrfCoordinator; } /** * @notice fulfillRandomness handles the VRF response. Your contract must * @notice implement it. See "SECURITY CONSIDERATIONS" above for important * @notice principles to keep in mind when implementing your fulfillRandomness * @notice method. * * @dev VRFConsumerBaseV2 expects its subcontracts to have a method with this * @dev signature, and will call it once it has verified the proof * @dev associated with the randomness. (It is triggered via a call to * @dev rawFulfillRandomness, below.) * * @param requestId The Id initially returned by requestRandomness * @param randomWords the VRF output expanded to the requested number of words */ function fulfillRandomWords(uint256 requestId, uint256[] memory randomWords) internal virtual; // rawFulfillRandomness is called by VRFCoordinator when it receives a valid VRF // proof. rawFulfillRandomness then calls fulfillRandomness, after validating // the origin of the call function rawFulfillRandomWords(uint256 requestId, uint256[] memory randomWords) external { if (msg.sender != vrfCoordinator) { revert OnlyCoordinatorCanFulfill(msg.sender, vrfCoordinator); } fulfillRandomWords(requestId, randomWords); } }