哈希锁定, 全称为哈希时间锁定合约, 英文为 HTLC（Hash TimeLock Contract）, 是解决跨链的一种技术方案. 指在智能合约的基础上, 让双方先锁定资产, 如果都在规定的时间内输入正确哈希值的原值, 即可完成交易.
哈希锁定的实现的两个条件, 一个是哈希锁, 一个是时间锁, 必须同时满足这两个条件, 才能完成交易, 如果不能满足条件, 代币会自动返回, 不收手续费.
小白生成随机数, 并发送 Hash 给小黑, 同时小白在它链 A 上锁定币, 设定交易的时间, 小黑收到 Hash 后, 在它链 B 上锁定币, 也设置时间限制. 小白看到小黑的锁定后, 在规定时间内, 发送包含之前的随机数的认领协议给小黑, 小黑收到后在规定时间内给出哈希值后, 锁定的数字货币立即释放, 完成交易.
哈希锁定的优点: 实现了跨链资产的交换, 可以不用公证人. 哈希锁定的缺点: 没有实现跨链资产的转移, 更不能实现跨链合约的执行.
- newContract
开启一个 Hash 时间锁, 同时存入 ETH, 付款人各自在不同的链上调用, _receiver 需要传入收款人的地址.
/**
* @dev Sender sets up a new hash time lock contract depositing the ETH and
* providing the reciever lock terms.
*
* @param _receiver Receiver of the ETH.
* @param _hashlock A sha-2 sha256 hash hashlock.
* @param _timelock UNIX epoch seconds time that the lock expires at.
* Refunds can be made after this time.
* @return contractId Id of the new HTLC. This is needed for subsequent
* calls.
*/
function newContract(address payable _receiver, bytes32 _hashlock, uint _timelock)
external
payable
fundsSent
futureTimelock(_timelock)
returns (bytes32 contractId)
{
contractId = sha256(
abi.encodePacked(
msg.sender,
_receiver,
msg.value,
_hashlock,
_timelock
)
);
// Reject if a contract already exists with the same parameters. The
// sender must change one of these parameters to create a new distinct
// contract.
if (haveContract(contractId))
revert("Contract already exists");
contracts[contractId] = LockContract(
msg.sender,
_receiver,
msg.value,
_hashlock,
_timelock,
false,
false,
0x0
);
emit LogHTLCNew(
contractId,
msg.sender,
_receiver,
msg.value,
_hashlock,
_timelock
);
}- withdraw
收款人调用. 传入 contractID 和 Hash 对应的原始值后面, 收款人就可以收到对应的款项.
/**
* @dev Called by the receiver once they know the preimage of the hashlock.
* This will transfer the locked funds to their address.
*
* @param _contractId Id of the HTLC.
* @param _preimage sha256(_preimage) should equal the contract hashlock.
* @return bool true on success
*/
function withdraw(bytes32 _contractId, bytes32 _preimage)
external
contractExists(_contractId)
hashlockMatches(_contractId, _preimage)
withdrawable(_contractId)
returns (bool)
{
LockContract storage c = contracts[_contractId];
c.preimage = _preimage;
c.withdrawn = true;
c.receiver.transfer(c.amount);
emit LogHTLCWithdraw(_contractId);
return true;
}- refund
付款人调用. 当收款人在规定的时间内没有调用 withdraw 提取款项时, 收款人可以调用这个 refund 方法把款项取回.
/**
* @dev Called by the sender if there was no withdraw AND the time lock has
* expired. This will refund the contract amount.
*
* @param _contractId Id of HTLC to refund from.
* @return bool true on success
*/
function refund(bytes32 _contractId)
external
contractExists(_contractId)
refundable(_contractId)
returns (bool)
{
LockContract storage c = contracts[_contractId];
c.refunded = true;
c.sender.transfer(c.amount);
emit LogHTLCRefund(_contractId);
return true;
}这两个合约功能和 HashedTimelock 功能相同, 区别在于 HashedTimelock 存入的是 ETH, HashedTimelockERC20 和 HashedTimelockERC721 存入是 ERC20 和 ERC721, 同时在存入前需要预先授权 approve 给 HashedTimelockERC20 和 HashedTimelockERC721 合约.
- 安装依赖
yarn- 测试 HashedTimelock
npx hardhat test/HashedTimelock.js- 哈希时间锁详解: https://yuanxuxu.com/2020/08/05/%E5%8C%BA%E5%9D%97%E9%93%BE%E8%B7%A8%E9%93%BE%E6%8A%80%E6%9C%AF%E4%B9%8B%E5%93%88%E5%B8%8C%E6%97%B6%E9%97%B4%E9%94%81/
- 哈希时间锁原理: https://learnblockchain.cn/article/2152
- 哈希时间锁代码样例: https://github.com/chatch/hashed-timelock-contract-ethereum/blob/master/test/htlcERC20.js
- 跨链技术介绍：https://medium.com/electron-labs/what-is-bdlc-and-how-it-works-5716fbbacde8
- 轻客户端介绍： https://blog.ethereum.org/2015/01/10/light-clients-proof-stake/
- 跨链下半场究竟都怎么跨？跨什么？:https://mirror.xyz/0x22034f804960B9B34353d6A7595cC4E83ac0daBe/cu5_hT-WPNZCNtpbPUzp0O9LKGk-pepF5I5s3SDbKTw
- 跨链的简要研究：从原理到技术: https://zhuanlan.zhihu.com/p/92667917