Multi-party Fair Exchange Protocol with Smart Contract on Bitcoin

Traditional multi-party exchange protocols need a third party to ensure fairness. It can bring some communication costs and cryptanalytic attacks. In recent years, researchers have focused on blockchain to design a fair exchange protocol without a central authority. So far, there are a few works on fair exchange protocols for any topology based on bitcoin. This paper puts forward a decentralized protocol for star topology based on the bitcoin, that is, our protocol does not contain a third party. Communication costs, information disclosure, and cryptanalytic attacks are not considered for the third party. These features greatly reduce the burden and increase the efficiency of the protocol. To guarantee the fairness, a commitment scheme is provided. And the proposed protocol constructs an ideal function as a smart contract. The bitcoin is automatically transferred in the limited time instead of manual operations. Security analysis shows that our construction can guarantee fairness, resist double spending and sybil attack. Meanwhile, the proposed protocol enjoys high efficiency. Moreover, with a slight modification, our protocol can be extended to apply to any topology.