Abstract: Sub-protocols are crucial to the fairness of offline fair exchange protocols. The strand space model analyze in the ASW offline protocol and the KM offline protocol. Analysis shows that keeping the sub-protocols’ executions mutual exclusive and their result synchronization is important for guaranteeing the fairness of offline fair exchange protocols. Based on the analysis, this paper proposes some improvements to solve the problems found in the protocols, and makes suggestions on designing future offline fair exchange protocols.

Key words: fair exchange, sub-protocol, strand space, offline Trusted Third Party(TTP), protocol design

摘要： 离线公平交换协议的子协议对其公平性至关重要。使用串空间方法分析2个重要的离线公平交换协议的子协议对协议公平性的影响，发现保持子协议运行的互斥和结果的同步是离线公平交换协议公平性的重要保证。根据该发现，针对协议中存在的问题，给出协议的改进方案，提出设计两方和多方离线公平交换协议的建议。

关键词: 公平交换, 子协议, 串空间, 离线可信第三方, 协议设计

CLC Number: 

• TP309