Communication complexity of byzantine agreement, revisited

Ittai Abraham, T. H.Hubert Chan, Danny Dolev, Kartik Nayak, Rafael Pass, Ling Ren, Elaine Shi

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


As Byzantine Agreement (BA) protocols find application in large-scale decentralized cryptocurrencies, an increasingly important problem is to design BA protocols with improved communication complexity. A few existing works have shown how to achieve subquadratic BA under an adaptive adversary. Intriguingly, they all make a common relaxation about the adaptivity of the attacker, that is, if an honest node sends a message and then gets corrupted in some round, the adversary cannot erase the message that was already sent - henceforth we say that such an adversary cannot perform "after-the-fact removal". By contrast, many (super-)quadratic BA protocols in the literature can tolerate after-the-fact removal. In this paper, we first prove that disallowing after-the-fact removal is necessary for achieving subquadratic-communication BA. Next, we show a new subquadratic binary BA construction (of course, assuming no after-the-fact removal) that achieves near- optimal resilience and expected constant rounds under standard cryptographic assumptions and a public-key infrastructure (PKI). In comparison, all known subquadratic protocols make additional strong assumptions such as random oracles or the ability of honest nodes to erase secrets from memory, and even with these strong assumptions, no prior work can achieve the above properties. Lastly, we show that some setup assumption is necessary for achieving subquadratic multicast-based BA.

Original languageEnglish (US)
Title of host publicationPODC 2019 - Proceedings of the 2019 ACM Symposium on Principles of Distributed Computing
PublisherAssociation for Computing Machinery
Number of pages10
ISBN (Electronic)9781450362177
StatePublished - Jul 16 2019
Externally publishedYes
Event38th ACM Symposium on Principles of Distributed Computing, PODC 2019 - Toronto, Canada
Duration: Jul 29 2019Aug 2 2019

Publication series

NameProceedings of the Annual ACM Symposium on Principles of Distributed Computing


Conference38th ACM Symposium on Principles of Distributed Computing, PODC 2019


  • Adaptive
  • Byzantine agreement
  • Communication complexity
  • Lower bound
  • Multicast

ASJC Scopus subject areas

  • Software
  • Hardware and Architecture
  • Computer Networks and Communications


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