timed commitment using ethereum blockchain

Question

I read this paper: https://eprint.iacr.org/2013/784.pdf

that introduces the idea of a Bitcoin-based time commitment scheme. In which if the committer does not open his commitment before a specific time t, the other party can fine him some bitcoins so the committer is enforced to open the commitment before time t. Is that kind of time commitment is available using ethereum smart contacts?

This article speaks about committing and reveal on etherum https://medium.com/gitcoin/commit-reveal-scheme-on-ethereum-25d1d1a25428

Answer 1

This code is nearly identical to my answer here: Zero knowledge contingent payment on etherum?. The changes mostly involved renaming variables, but the core concept is the same:

• ether is escrowed
• if the preimage is revealed before the deadline, the funds go to one account
• if the preimage is not revealed before the deadline, the funds go to a different account

pragma solidity 0.5.2;

contract TimedCommitment {
    address payable revealer;
    address payable fineRecipient;
    bytes32 public hash;
    uint256 public deadline;

    constructor(address payable _fineRecipient, bytes32 _hash, uint256 timeout) public payable {
        revealer = msg.sender;
        fineRecipient = _fineRecipient;

        hash = _hash;
        deadline = now + timeout;
    }

    // If this is called with the correct preimage, the revealer gets their funds back.
    function providePreimage(bytes calldata preimage) external {
        require(keccak256(preimage) == hash);
        revealer.transfer(address(this).balance);
    }

    // Pay the fine to the fineRecipient if the timeout has expired.
    function refund() external {
        require(msg.sender == fineRecipient);
        require(now >= deadline);

        msg.sender.transfer(address(this).balance);
    }
}