HT²REP: A fair cross-chain atomic exchange protocol under UC framework based on HTLCs and TRE

Cross-chain transactions between heterogeneous blockchain systems pose various challenges, encompassing atomicity, security, and fairness of the transactions. While Traditional Hash Time Lock Contracts (HTLCs) can achieve atomic cross-chain transactions, they exhibit fairness deficiencies in two aspects: firstly, the transaction initiator benefits from an American Option (AO) advantage, and secondly, the transaction responder may be incentivized to launch a Draining Attack (DA), both of which impact the fairness of cross-chain transactions. Because of significant fluctuations in the exchange rate of tokens held by both parties, cross-chain transactions often face timeout rollbacks, resulting in a diminished probability of successful transactions. To tackle these issues, we propose a novel atomic cross-chain exchange protocol—HT2REP. This protocol integrates Time Released Encryption (TRE), ShangMi 3 Hash function (SM3), and scalable smart contract technologies to enhance fairness within the traditional HTLCs protocol. Additionally, HT2REP ensures atomicity, security, and a heightened probability of success for cross-chain exchanges. Finally, we demonstrate that HT2REP is Universally Composable (UC) secure.