Isolated Proofs of Knowledge and Isolated Zero Knowledge

We introduce a new notion called -isolated proofs of knowledge ( -IPoK). These are proofs of knowledge where a cheating prover is allowed to exchange up to bits of communication with some external adversarial environment during the run of the proof. Without any additional setup assumptions, no witness hiding protocol can be an -IPoK for unbounded values of . However, for any pre-defined threshold , and any relation in NP and we construct an -IPoK protocol for that relation. The resulting protocols are zero knowledge (ZK) in the standard sense, i.e., w.r.t. a verifier that communicates only with the prover during the proof. The cost of having a large threshold is a large communication complexity of the constructed protocol. We analyze these costs and present a solution that is asymptotically optimal. If a cheating verifier is allowed to communicate arbitrarily with an external environment, it is not possible to construct an -IPoK that is also ZK with respect to such a verifier. As anoth...

• Type: Conference
• Year: 2008
• Where: EUROCRYPT
• Authors: Ivan Damgård, Jesper Buus Nielsen, Daniel Wichs
• Keywords: -ipok Protocols, Cryptology, EUROCRYPT 2008, Verifiers, Zero Knowledge