Improved extension protocols for byzantine broadcast and agreement

Kartik Nayak, Ling Ren, Elaine Shi, Nitin H. Vaidya, Zhuolun Xiang

Research output: Chapter in Book/Report/Conference proceedingConference contribution


Byzantine broadcast (BB) and Byzantine agreement (BA) are two most fundamental problems and essential building blocks in distributed computing, and improving their efficiency is of interest to both theoreticians and practitioners. In this paper, we study extension protocols of BB and BA, i.e., protocols that solve BB/BA with long inputs of l bits using lower costs than l single-bit instances. We present new protocols with improved communication complexity in almost all settings: authenticated BA/BB with t < n/2, authenticated BB with t < (1 − ε)n, unauthenticated BA/BB with t < n/3, and asynchronous reliable broadcast and BA with t < n/3. The new protocols are advantageous and significant in several aspects. First, they achieve the best-possible communication complexity of Θ(nl) for wider ranges of input sizes compared to prior results. Second, the authenticated extension protocols achieve optimal communication complexity given the current best available BB/BA protocols for short messages. Third, to the best of our knowledge, our asynchronous and authenticated protocols in the setting are the first extension protocols in that setting.

Original languageEnglish (US)
Title of host publication34th International Symposium on Distributed Computing, DISC 2020
EditorsHagit Attiya
PublisherSchloss Dagstuhl- Leibniz-Zentrum fur Informatik GmbH, Dagstuhl Publishing
ISBN (Electronic)9783959771689
StatePublished - Oct 1 2020
Event34th International Symposium on Distributed Computing, DISC 2020 - Virtual, Online
Duration: Oct 12 2020Oct 16 2020

Publication series

NameLeibniz International Proceedings in Informatics, LIPIcs
ISSN (Print)1868-8969


Conference34th International Symposium on Distributed Computing, DISC 2020
CityVirtual, Online


  • Byzantine agreement
  • Byzantine broadcast
  • Communication complexity
  • Extension protocol

ASJC Scopus subject areas

  • Software


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