A One-Round, Two-Prover, Zero-Knowledge Protocol for NP

The model of zero knowledge multi prover interactive proofs was introduced by Ben-Or, Goldwasser, Kilian and Wigderson. A major open problem associated with these protocols is whether they can be executed in parallel. A positive answer was claimed by Fortnow, Rompel and Sipser, but its proof was later shown to be flawed by Fortnow who demonstrated that the probability of cheating in n independent parallel rounds can be exponentially higher than the probability of cheating in n independent sequential rounds. In this paper we use refined combinatorial arguments to settle this problem by proving that the probability of cheating in a parallelized BGKW protocol is at most 1/2n/9, and thus every problem in NP has a one-round two prover protocol which is perfectly zero knowledge under no cryptographic assumptions.