The Strong Link Graph for Enhancing Sybil Defenses

The sybil problem is a fundamental problem in distributed systems and online social networks (OSNs). The basic problem is that an attacker can easily create multiple identities in a distributed or open online system. Popular and effective sybil defenses are usually based on properties of the network structure. However, most defenses assume that it is hard for the attacker to make many connections to honest users. However, this assumption can be invalid in real OSNs which decreases the effectiveness of many sybil defenses. We propose a graph transformation, the strong link graph, to mitigate such attacks by reducing the effect ofa large number of attack edges. Our preliminary experiments show indeed that when the attacker has many attack edges, existing algorithms such as SybilLimit, SybilRank and Gatekeeper are ineffective. After the strong link graph is applied, it deletes many of the attack edges, restoring the effectiveness of the sybil defenses.