Removing complexity assumptions from concurrent zero-knowledge proofs

Abstract

Zero-knowledge proofs are a powerful tool for the construc-tion of several types of cryptographic protocols. Recently, motivated by practical considerations, such protocols have been investigated in a con-current and asynchronous distributed model, where protocols have been proposed relying on various synchronization assumptions and unproven complexity assumptions. In this paper we present the rst constructions of proof systems that are concurrent zero-knowledge without relying on unproven complexity as-sumptions. Our techniques transform a non-concurrent zero-knowledge protocol into a concurrent zero-knowledge one. They apply to large classes of languages and preserve the type of zero-knowledge: if the origi-nal protocol is computational, statistical or perfect zero-knowledge, then so is the transformed one.