Removing Complexity Assumptions from Concurrent Zero-Knowledge Proofs

Abstract

Zero-knowledge proofs are a powerful tool for the construction of several types of cryptographic protocols. Recently, motivated by practical considerations, such protocols have been investigated in a concurrent and asynchronous distributed model, where protocols have been proposed relying on various synchronization assumptions and unproven complexity assumptions. In this paper we present the first constructions of proof systems that are concurrent zero-knowledge without relying on unproven complexity assumptions. 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 original protocol is computational, statistical or perfect zero-knowledge, then so is the transformed one.