tokenbridge-contracts/contracts/libraries/Message.sol

pragma solidity 0.4.24;
import "../interfaces/IBridgeValidators.sol";

library Message {
    function addressArrayContains(address[] array, address value) internal pure returns (bool) {
        for (uint256 i = 0; i < array.length; i++) {
            if (array[i] == value) {
                return true;
            }
        }
        return false;
    }
    // layout of message :: bytes:
    // offset  0: 32 bytes :: uint256 - message length
    // offset 32: 20 bytes :: address - recipient address
    // offset 52: 32 bytes :: uint256 - value
    // offset 84: 32 bytes :: bytes32 - transaction hash
    // offset 116: 20 bytes :: address - contract address to prevent double spending

    // mload always reads 32 bytes.
    // so we can and have to start reading recipient at offset 20 instead of 32.
    // if we were to read at 32 the address would contain part of value and be corrupted.
    // when reading from offset 20 mload will read 12 bytes (most of them zeros) followed
    // by the 20 recipient address bytes and correctly convert it into an address.
    // this saves some storage/gas over the alternative solution
    // which is padding address to 32 bytes and reading recipient at offset 32.
    // for more details see discussion in:
    // https://github.com/paritytech/parity-bridge/issues/61
    function parseMessage(bytes message)
        internal
        pure
        returns (address recipient, uint256 amount, bytes32 txHash, address contractAddress)
    {
        require(isMessageValid(message));
        assembly {
            recipient := mload(add(message, 20))
            amount := mload(add(message, 52))
            txHash := mload(add(message, 84))
            contractAddress := mload(add(message, 104))
        }
    }

    function isMessageValid(bytes _msg) internal pure returns (bool) {
        return _msg.length == requiredMessageLength();
    }

    function requiredMessageLength() internal pure returns (uint256) {
        return 104;
    }

    function recoverAddressFromSignedMessage(bytes signature, bytes message, bool isAMBMessage)
        internal
        pure
        returns (address)
    {
        require(signature.length == 65);
        bytes32 r;
        bytes32 s;
        bytes1 v;

        assembly {
            r := mload(add(signature, 0x20))
            s := mload(add(signature, 0x40))
            v := mload(add(signature, 0x60))
        }
        require(uint8(v) == 27 || uint8(v) == 28);
        require(uint256(s) <= 0x7FFFFFFFFFFFFFFFFFFFFFFFFFFFFFFF5D576E7357A4501DDFE92F46681B20A0);

        return ecrecover(hashMessage(message, isAMBMessage), uint8(v), r, s);
    }

    function hashMessage(bytes message, bool isAMBMessage) internal pure returns (bytes32) {
        bytes memory prefix = "\x19Ethereum Signed Message:\n";
        if (isAMBMessage) {
            return keccak256(abi.encodePacked(prefix, uintToString(message.length), message));
        } else {
            string memory msgLength = "104";
            return keccak256(abi.encodePacked(prefix, msgLength, message));
        }
    }

    /**
    * @dev Validates provided signatures, only first requiredSignatures() number
    * of signatures are going to be validated, these signatures should be from different validators.
    * @param _message bytes message used to generate signatures
    * @param _signatures bytes blob with signatures to be validated.
    * First byte X is a number of signatures in a blob,
    * next X bytes are v components of signatures,
    * next 32 * X bytes are r components of signatures,
    * next 32 * X bytes are s components of signatures.
    * @param _validatorContract contract, which conforms to the IBridgeValidators interface,
    * where info about current validators and required signatures is stored.
    * @param isAMBMessage true if _message is an AMB message with arbitrary length.
    */
    function hasEnoughValidSignatures(
        bytes _message,
        bytes _signatures,
        IBridgeValidators _validatorContract,
        bool isAMBMessage
    ) internal view {
        require(isAMBMessage || isMessageValid(_message));
        uint256 requiredSignatures = _validatorContract.requiredSignatures();
        uint256 amount;
        assembly {
            amount := and(mload(add(_signatures, 1)), 0xff)
        }
        require(amount >= requiredSignatures);
        bytes32 hash = hashMessage(_message, isAMBMessage);
        address[] memory encounteredAddresses = new address[](requiredSignatures);

        for (uint256 i = 0; i < requiredSignatures; i++) {
            uint8 v;
            bytes32 r;
            bytes32 s;
            uint256 posr = 33 + amount + 32 * i;
            uint256 poss = posr + 32 * amount;
            assembly {
                v := mload(add(_signatures, add(2, i)))
                r := mload(add(_signatures, posr))
                s := mload(add(_signatures, poss))
            }

            address recoveredAddress = ecrecover(hash, v, r, s);
            require(_validatorContract.isValidator(recoveredAddress));
            require(!addressArrayContains(encounteredAddresses, recoveredAddress));
            encounteredAddresses[i] = recoveredAddress;
        }
    }

    function uintToString(uint256 i) internal pure returns (string) {
        if (i == 0) return "0";
        uint256 j = i;
        uint256 length;
        while (j != 0) {
            length++;
            j /= 10;
        }
        bytes memory bstr = new bytes(length);
        uint256 k = length - 1;
        while (i != 0) {
            bstr[k--] = bytes1(48 + (i % 10));
            i /= 10;
        }
        return string(bstr);
    }
}