Sybil-resistance

The property of a system that raises the cost of presenting many distinct identities, so that one actor cannot cheaply appear as many. No open system achieves it categorically (Douceur, 2002); the realistic goal is to make a credible additional identity cost the attacker something real. This book treats Sybil-resistance not as a single mechanism but as a property the four families collectively confer — reputation, costly identity, proof of personhood, and accountability — composed for the room at hand. Most individual mechanisms (EigenTrust, social-graph personhood, aggregators) are conditionally rather than categorically Sybil-resistant.