Precise Zero-Knowledge in Concurrent Setting

We present a stronger notion of zero-knowledge: precise concurrent zero-knowledge. Our notion captures the idea that the view of any verifier in concurrent interaction can be reconstructed in the almost same time (within a constant/polynomial factor). Precise zero-knowledge in stand-alone setting was introduced by Micali and Pass in STOC’06 (The original work used the term ”local zero-knowledge”.). Their notion shows that the view of any verifier can be reconstructed in the almost same time in stand-alone setting. Hence our notion is the generalization of their notion in concurrent setting. Furthermore, we propose a ω(log n)-round concurrent zero-knowledge argument for NP with linear precision, which shows that the view of any verifier in concurrent interaction can be reconstructed by the simulator with linear-time overhead. Our argument is Feige-Lapidot-Shamir type which consists of a proof-preamble and a proof-body for a modified NP statement. Our result assumes the restriction of adversarial scheduling the communication that the concurrent interaction of preambles of all sessions will be scheduled before any proof-body by the adversarial verifier.