A Game-Theoretic Analysis of Trust Management in P2P Systems

This paper reports some Braess-like paradoxes in peer-to-peer (P2P) trust management systems. We use the tools from game theory to model and analyze the reporting and exclusion processes and show how uncertainty and belief among peers might lead to surprising and unexpected peer behaviors, which, in turn, could make current P2P trust management systems ineffective. The contributions of the paper are the followings. First, we find that if a reputation system is not incentive-compatible, the more the number of peers in the system, the less likely that anyone will report about a malicious peer. Second, we address the issue of voting for exclusion of a (maliciously believed) peer and provide an analysis of the problem. By modeling the decision process as a Bayesian game, we find that the possible application of exclusion in P2P system might be dangerous. More precisely, our analysis shows that, under certain assumptions, the more the number of voting peers, the more likely that an innocent peer is excluded from the network. Finally, in the lights of the investigated paradoxes, we discuss possible solutions to improve the efficiency of current trust management systems in P2P networks.