Cryptology ePrint Archive: Report 2006/065

On Expected Constant-Round Protocols for Byzantine Agreement

Jonathan Katz and Chiu-Yuen Koo

Abstract: In a seminal paper, Feldman and Micali (STOC '88) show an $n$-party Byzantine agreement protocol tolerating $t < n/3$ malicious parties that runs in expected constant rounds. Here, we show an expected constant-round protocol for authenticated Byzantine agreement assuming honest majority (i.e., $t < n/2$), and relying only on the existence of a secure signature scheme and a public-key infrastructure (PKI). Combined with existing results, this gives the first expected constant-round protocol for secure computation with honest majority in a point-to-point network assuming only one-way functions and a PKI. Our key technical tool --- a new primitive we introduce called moderated VSS --- also yields a simpler proof of the Feldman-Micali result.

We also show a simple technique for sequential composition of protocols without simultaneous termination (something that is inherent for Byzantine agreement protocols using $o(n)$ rounds) for the case of $t<n/2$.

Category / Keywords: cryptographic protocols / distributed computing, multiparty computation

Publication Info: An extended abstract will appear at Crypto 2006

Date: received 20 Feb 2006, last revised 23 May 2006

Contact author: jkatz at cs umd edu

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Version: 20060523:192113 (All versions of this report)

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