## Cryptology ePrint Archive: Report 2001/107

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

Yehuda Lindell

Abstract: In this paper we show that any {\em two-party} functionality can be securely computed in a {\em 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 {\em 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).

Category / Keywords: cryptographic protocols / Secure two-party computation, constant-round protocols, coin-tossing

Publication Info: An extended abstract appeared at CRYPTO 2001.

Date: received 13 Dec 2001, last revised 9 Oct 2003

Contact author: lindell at wisdom weizmann ac il

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