Informant: Detecting Sybils Using Incentives

We propose an economic approach to Sybil attack detection. In our Informant protocol, a detective offers a reward for Sybils to reveal themselves. The detective accepts from one identity a security deposit and the name of target peer; the deposit and a reward are given to the target. We prove the optimal strategy for the informant is to play the game if and only if she is Sybil with a low opportunity cost, and the target will cooperate if and only if she is identical to the informant. Informant uses a Dutch auction to find the minimum possible reward that will reveal a Sybil attacker. Because our approach is economic, it is not limited to a specific application and does not rely on a physical device or token.