Game theoretic analyses for free-riding and whitewashing in P2P systems

Conventional P2P networks do not provide incentives for users. Therefore, users can easily obtain information without themselves contributing any information or service to a P2P community. This leads to the well known free-riding problem. Reputation systems may impose penalties on free-riders to identify and distinguish them from contributors, but these systems are vulnerable to the whitewashing attack. This paper analyzed the Tit-for-Tat protocol in the presence of whitewashers using a game theoretic approach. The Tit-for-Tat protocol is not an evolutionary stable strategy against invasion of whitewashing, but imposing an appropriate identity cost helps in preventing invasion by whitewashers. Simulation results demonstrated the theoretic analysis, and showed that the percentage of cooperating nodes in P2P networks with an appropriate identity cost is nearly four times bigger than without any identity cost.