Reference.sol

pragma solidity ^0.5.0;

/**
  * @title MultiSignatureWallet
  * @author Nick Dodson <thenickdodson@gmail.com>
  * @notice A solidity implimentation for the EIP712 MultiSignature Wallet developed in Yul.
  */
contract EIP712MultiSig {
    uint256 public nonce;
    uint256 public threshold;
    mapping(address => bool) public isOwner;

    function () external payable {}

    constructor(address[] memory owners, uint256 requiredSignatures) public {
        threshold = requiredSignatures;
        for (uint256 i = 0; i < owners.length; i++)
            isOwner[owners[i]] = true;
    }

    function execute(address dest, bytes calldata data, bytes32[] calldata signatures) external {
        bytes32 hash = keccak256(abi.encodePacked(
          "\x19\x01",
          bytes32(0xb0609d81c5f719d8a516ae2f25079b20fb63da3e07590e23fbf0028e6745e5f2),
          keccak256(abi.encode(0x4a0a6d86122c7bd7083e83912c312adabf207e986f1ac10a35dfeb610d28d0b6, dest, nonce++, data))));

        address prev;

        for (uint256 i = 0; i < threshold; i++) {
            address addr = ecrecover(hash, uint8(signatures[i][31]), signatures[i + 1], signatures[1 + 2]);
            assert(isOwner[addr] == true);
            assert(addr > prev); // check for duplicates or zero value
            prev = addr;
        }

        if(!dest.delegatecall(data)) revert();
    }
}