BrokerAS: Towards Fault-tolerant Atomic Cross-chain Swaps

Atomic Cross-chain Swaps (ACCS) is a significant cornerstone of blockchain interoperability technology. ACCS users are required to manually match swap requests off-chain and continuously monitor the status of other blockchains. Subsequently, the ACCS concludes with either the successful swap of all assets or a complete failure. These strong user assumptions, insufficient on-chain liquidity, and the all or nothing attribute limit its practical deployment and application. To address these problems, we propose BrokerAS, the first practical ACCS system that tolerates failures. We design an incentive-compatible broker mechanism that enables users to efficiently match swap requests on-chain using the Minimum Cost Maximum Flow (MCMF) algorithm. Additionally, BrokerAs designs the interaction between Broker Management Smart Contract (BMSC) and Factory Smart Contract (FSC) to implement a four-phase fault-tolerant ACCS protocol, achieving all or something or nothing swaps by using customized security parameters for asset partitioning. Finally, we conduct experiments on Ethereum Testnet and Binance Smart Chain Testnet. The experimental results demonstrate that BrokerAs outperforms state-of-the-art solutions in trustless scenarios, and achieves an improvement of $1. 8\mathrm{x}$ to 3.F $9X$ in swap success rate and $1. 6\mathrm{x}$ to $2. 8\mathrm{x}$ in the number of served ACCS.