Probabilistic analysis of the ASW protocol using PRISM

Increased interest in e-commerce protocols and reliable exchange of information over the Internet have created needs of fair exchange protocols for contract signing and other purposes. The ASW protocol is one of the prominent optimistic fair exchange protocols that is used for contract signing between two participants, the originator and the responder, with the aid of a trusted third party in case of a dispute. In our study, we have analyzed the key security objectives of ASW protocol, fairness, effectiveness and timeliness, using a probabilistic model checking tool, PRISM. First, we model the roles of the participants and the trusted third party in PRISM code. Next, we express the security objectives using a temporal logic, PCTL. Finally, the model is analyzed using these PCTL expressions; different outputs confirm the fairness of the ASW protocol. Moreover, the effectiveness and the timeliness of the protocol are also established.