soliditysignatures.sol

pragma solidity ^0.4.22;

contract ECVerify {
    function ecrecovery(bytes32 hash, bytes sig) public pure returns (address) {
        bytes32 r;
        bytes32 s;
        uint8 v;

        if (sig.length != 65) {
            return 0;
        }

        assembly {
            r := mload(add(sig, 32))
            s := mload(add(sig, 64))
            v := and(mload(add(sig, 65)), 255)
        }

        // https://github.com/ethereum/go-ethereum/issues/2053
        if (v < 27) v += 27;
        if (v != 27 && v != 28) return 0;
        return ecrecover(hash, v, r, s);
    }

    function verifySignature(bytes32 hash, bytes sig, address signer) public pure returns (bool) {
        return signer == ecrecovery(hash, sig);
    }
}


contract Test is ECVerify {
    
    address alice = 0x1B326Ad348e19ecFd1406C43D3bF7a95547AC55c;

    function hashHello() public pure returns(bytes32) {
        return keccak256("hello");
    }
    
    function checkSignature(bytes sig) public view returns(bool) {
        bytes32 hash = hashHello();
        return verifySignature( hash, sig, alice );
    }
}