Paper 2006/065

On Expected Constant-Round Protocols for Byzantine Agreement

Jonathan Katz and Chiu-Yuen Koo


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 $t<n/2$.

Available format(s)
Cryptographic protocols
Publication info
Published elsewhere. An extended abstract will appear at Crypto 2006
distributed computingmultiparty computation
Contact author(s)
jkatz @ cs umd edu
2006-05-23: revised
2006-02-23: received
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      author = {Jonathan Katz and Chiu-Yuen Koo},
      title = {On Expected Constant-Round Protocols for Byzantine Agreement},
      howpublished = {Cryptology ePrint Archive, Paper 2006/065},
      year = {2006},
      note = {\url{}},
      url = {}
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