Everything in NP can be argued in perfect zero-knowledge in a bounded number of rounds

Abstract

A perfect zero-knowledge interactive protocol allows a prover to convince a verifier of the validity of a statement in a way that does not give the verifier any additional information [GMR, GMW]. Such protocols take place by the exchange of messages back and forth between the prover and the verifier. An important measure of efficiency for these protocols is the number of rounds in the interaction. In previously known perfect zero-knowledge protocols for statements concerning NP-complete problems [BCC], at least k rounds were necessary in order to prevent one party from having a probability of undetected cheating greater than 2-k. In the full version of this paper [BCY], we give the first perfect zero-knowledge protocol that offers arbitrarily high security for any statement in NP with a constant number of rounds (under a suitable cryptographic assumption). This protocol is a BCC-argument rather than a GMR-proof [BC3], as are all the known perfect zero-knowledge protocols for NP-complete problems [BCC].