Privacy Pool 智能合約實作

承諾方案

// Pedersen 承諾
function commit(uint256 value, uint256 randomness) 
    public pure returns (bytes32) {
    return keccak256(abi.encodePacked(value, randomness));
}

核心合約

contract PrivacyPool {
    mapping(bytes32 => bool) public commitments;
    mapping(bytes32 => bool) public nullifiers;
    
    function deposit(bytes32 commitment) external payable {
        commitments[commitment] = true;
    }
    
    function withdraw(
        bytes calldata proof,
        bytes32 nullifierHash
    ) external {
        require(!nullifiers[nullifierHash]);
        require(verifyProof(proof));
        nullifiers[nullifierHash] = true;
        msg.sender.transfer(msg.value);
    }
}

Merkle 樹驗證

template MerkleTree(depth) {
    signal input leaf;
    signal input root;
    signal input pathElements[depth];
    
    hash[0] === leaf;
    for (i = 0; i < depth; i++) {
        hash[i+1] === hashLeftRight(hash[i], pathElements[i]);
    }
    hash[depth] === root;
}

結語

合約安全要審計，資金安全無小事。

COMMIT: Add Privacy Pool smart contract implementation guide