Parallel Coin-Tossing and Constant-Round Secure Two-Party Computation

Yehuda Lindell

Carmit Hazay, Avishay Yanai

Carmit Hazay, Avishay Yanai

Yehuda Lindell

Abstract. In this paper we show that any two-party functionality can be securely computed in a constant number of rounds, where security is obtained against malicious adversaries that may arbitrarily deviate from the protocol specification. This is in contrast to Yao’s constant-round protocol that ensures security only in the face of semi-honest adversaries, and to its malicious adversary version that requires a polynomial number of rounds. In order to obtain our result, we present a constant-round protocol for secure coin-tossing of polynomially many coins (in parallel). We then show how this protocol can be used in conjunction with other existing constructions in order to obtain a constant-round protocol for securely computing any two-party functionality. On the subject of coin-tossing, we also present a constant-round perfect coin-tossing protocol, where by “perfect ” we mean that the resulting coins are guaranteed to be statistically close to uniform (and not just pseudorandom). 1

Amir Zarei, Staal A. Vinterbo

Xiaolan Zhang, Hong-xiang Sun, Hua Zhang +2 more

A coin-tossing protocol lets two parties decide on a string that should be a random (or at least pseudorandom) string. In this paper, we focus on taking advantage of the perfectly hiding commitment scheme, constant-round perfect zero-knowledge arguments and arguments of knowledge to construct a two-party constant-round perfect protocol for secure coin-tossing, where both of two parties can obtain the common resulting coins and the resulting coins are guaranteed to be statistically close to uniform. The security of our protocol is obtained against malicious non-uniform adversaries that may arbitrarily deviate from the protocol specification. Comparing with the Barak's protocol, we utilize the black-box reduction in the process of security proof and the rounds of our protocol decrease obviously.