Abstract

Abstract—Most existing large-scale networked systems on the Internet such as peer-to-peer systems are vulnerable to Sybil attacks where a single adversary can introduce many bogus identities. One promising defense of Sybil attacks is to perform social-network based admission control to bound the number of Sybil identities admitted. SybilLimit [22], the best known Sybil admission control mechanism, can restrict the number of Sybil identities admitted per attack edge to O(logn) with high probability assuming O(n/logn) attack edges. In this paper, we propose Gatekeeper, a decentralized Sybilresilient admission control protocol that significantly improves over SybilLimit. Gatekeeper is optimal for the case of O(1) attack edges and admits only O(1) Sybil identities (with high probability) in a random expander social networks (real-world social networks exhibit expander properties). In the face of O(k) attack edges (for any k ∈ O(n/logn)), Gatekeeper admits O(logk) Sybils per attack edge. This result provides a graceful continuum across the spectrum of attack edges. We demonstrate the effectiveness of Gatekeeper experimentally on real-world social networks and synthetic topologies. I.

Citations