An Extended Model of Rational Exchange Based on Dynamic Games of Imperfect Information

Abstract

The notion of rational exchange introduced by Syverson in 1998 is a particularly interesting alternative when an efficient scheme for fair exchange is required but the use of a trusted third party is not allowed. A rational exchange protocol cannot provide fairness, but it ensures that rational (i.e. self-interested) parties would have no reason to deviate from the protocol. Buttyán et al (2003) have recently pointed out how rationality in exchange protocols can be formalized and studied within the framework provided by Game Theory. In this paper, we identify some vulnerabilities in Syverson’s protocol which were not detected by Buttyán et al’s analysis. These motivate us to extend the model to consider new aspects, never formalized before when analyzing security protocols. These aspects are related to participants’ reputation, protocol’s robustness, and the impact that scenarios where the protocol is executed repeatedly have on the outcome of the protocol execution.