tornado-core/contracts/Mixer.sol

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pragma solidity ^0.5.8;
import "./MerkleTreeWithHistory.sol";
contract IVerifier {
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function verifyProof(uint256[2] memory a, uint256[2][2] memory b, uint256[2] memory c, uint256[4] memory input) public returns(bool);
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}
contract Mixer is MerkleTreeWithHistory {
uint256 public transferValue;
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mapping(uint256 => bool) public nullifierHashes;
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// we store all commitments just to prevent accidental deposits with the same commitment
mapping(uint256 => bool) public commitments;
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IVerifier verifier;
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event Deposit(uint256 indexed commitment, uint256 leafIndex, uint256 timestamp);
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event Withdraw(address to, uint256 nullifierHash, uint256 fee);
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/**
@dev The constructor
@param _verifier the address of SNARK verifier for this contract
@param _transferValue the value for all deposits in this contract in wei
*/
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constructor(
address _verifier,
uint256 _transferValue,
uint8 _merkleTreeHeight,
uint256 _emptyElement
) MerkleTreeWithHistory(_merkleTreeHeight, _emptyElement) public {
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verifier = IVerifier(_verifier);
transferValue = _transferValue;
}
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/**
@dev Deposit funds into mixer. The caller must send value equal to `transferValue` of this mixer.
@param commitment the note commitment, which is PedersenHash(nullifier + secret)
*/
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function deposit(uint256 commitment) public payable {
require(msg.value == transferValue, "Please send `transferValue` ETH along with transaction");
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require(!commitments[commitment], "The commitment has been submitted");
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_insert(commitment);
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commitments[commitment] = true;
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emit Deposit(commitment, next_index - 1, block.timestamp);
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}
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/**
@dev Withdraw deposit from the mixer. `a`, `b`, and `c` are zkSNARK proof data, and input is an array of circuit public inputs
`input` array consists of:
- merkle root of all deposits in the mixer
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- hash of unique deposit nullifier to prevent double spends
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- the receiver of funds
- optional fee that goes to the transaction sender (usually a relay)
*/
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function withdraw(uint256[2] memory a, uint256[2][2] memory b, uint256[2] memory c, uint256[4] memory input) public {
uint256 root = input[0];
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uint256 nullifierHash = input[1];
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address payable receiver = address(input[2]);
uint256 fee = input[3];
require(fee < transferValue, "Fee exceeds transfer value");
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require(!nullifierHashes[nullifierHash], "The note has been already spent");
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require(isKnownRoot(root), "Cannot find your merkle root"); // Make sure to use a recent one
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require(verifier.verifyProof(a, b, c, input), "Invalid withdraw proof");
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nullifierHashes[nullifierHash] = true;
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receiver.transfer(transferValue - fee);
if (fee > 0) {
msg.sender.transfer(fee);
}
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emit Withdraw(receiver, nullifierHash, fee);
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}
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function isSpent(uint256 nullifier) public view returns(bool) {
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return nullifierHashes[nullifier];
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}
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}