HashedSecretLockedContract

pragma solidity >0.4.99 <0.6.0;

library SafeMath {
    function mul(uint256 a, uint256 b) internal pure returns (uint256) {
        uint256 c = a * b;
        assert(a == 0 || c / a == b);
        return c;
    }

    function div(uint256 a, uint256 b) internal pure returns (uint256) {
        assert(b != 0);
        uint256 c = a / b;
        return c;
    }

    function sub(uint256 a, uint256 b) internal pure returns (uint256) {
        assert(b <= a);
        return a - b;
    }

    function add(uint256 a, uint256 b) internal pure returns (uint256) {
        uint256 c = a + b;
        assert(c >= a);
        return c;
    }
}

contract HashedSecretLockedContract {
    using SafeMath for uint256;
    address owner;
    bytes32 secret;
    uint256 value;
    
    constructor(bytes32 s) public {
        owner = msg.sender;
        secret = s;
        value = 0;
    }
    
    function fill() public payable {
        value = value.add(msg.value);
    }
    
    function retrieve(bytes32 guess) public payable {
        require(keccak256(abi.encodePacked(guess)) == secret);
        uint256 v = value;
        value = 0;
        msg.sender.transfer(v);
    }
    
    function hashForMe(bytes32 it) external pure returns (bytes32) {
        return keccak256(abi.encodePacked(it));
    }
}