diff --git a/contracts/ECRecovery.sol b/contracts/ECRecovery.sol new file mode 100644 index 0000000..87b15df --- /dev/null +++ b/contracts/ECRecovery.sol @@ -0,0 +1,68 @@ +pragma solidity ^0.5.0; + +/** + * @title Elliptic curve signature operations + * @dev Based on https://gist.github.com/axic/5b33912c6f61ae6fd96d6c4a47afde6d + * TODO Remove this library once solidity supports passing a signature to ecrecover. + * See https://github.com/ethereum/solidity/issues/864 + * Source: https://github.com/OpenZeppelin/openzeppelin-solidity/blob/master/contracts/ECRecovery.sol + */ +library ECRecovery { + /** + * @dev Recover signer address from a message by using their signature + * @param _hash bytes32 message, the hash is the signed message. What is recovered is the signer address. + * @param _signature bytes signature, the signature is generated using web3.eth.sign() + */ + function recover(bytes32 _hash, bytes memory _signature) + internal + pure + returns (address) + { + bytes32 r; + bytes32 s; + uint8 v; + + // Check the signature length + if (_signature.length != 65) { + return (address(0)); + } + + // Divide the signature in r, s and v variables + // ecrecover takes the signature parameters, and the only way to get them + // currently is to use assembly. + // solium-disable-next-line security/no-inline-assembly + assembly { + r := mload(add(_signature, 32)) + s := mload(add(_signature, 64)) + v := byte(0, mload(add(_signature, 96))) + } + + // Version of signature should be 27 or 28, but 0 and 1 are also possible versions + if (v < 27) { + v += 27; + } + + // If the version is correct return the signer address + if (v != 27 && v != 28) { + return (address(0)); + } else { + // solium-disable-next-line arg-overflow + return ecrecover(_hash, v, r, s); + } + } + + /** + * @dev prefix a bytes32 value with "\x19Ethereum Signed Message:" and hash the result + */ + function toEthSignedMessageHash(bytes32 _hash) + internal + pure + returns (bytes32) + { + // 32 is the length in bytes of hash, + // enforced by the type signature above + return keccak256( + abi.encodePacked("\x19Ethereum Signed Message:\n32", _hash) + ); + } +}