### Expected Constant Round Byzantine Broadcast under Dishonest Majority

Jun Wan, Hanshen Xiao, Elaine Shi, and Srinivas Devadas

##### Abstract

Byzantine Broadcast (BB) is a central question in distributed systems, and an important challenge is to understand its round complexity. Under the honest majority setting, it is long known that there exist randomized protocols that can achieve BB in expected constant rounds, regardless of the number of nodes $n$. However, whether we can match the expected constant round complexity in the corrupt majority setting --- or more precisely, when $f \geq n/2 + \omega(1)$ --- remains unknown, where $f$ denotes the number of corrupt nodes. In this paper, we are the first to resolve this long-standing question. We show how to achieve BB in expected $O((n/(n-f))^2)$ rounds. Our results hold under both a static adversary and a weakly adaptive adversary who cannot perform after-the-fact removal'' of messages already sent by a node before it becomes corrupt.

Available format(s)
Category
Cryptographic protocols
Publication info
Published elsewhere. MINOR revision.TCC 2020
Keywords
MulticastByzantine Agreement
Contact author(s)
junwan @ mit edu
runting @ gmail com
hsxiao @ mit edu
History
2020-10-19: last of 2 revisions
See all versions
Short URL
https://ia.cr/2020/590

CC BY

BibTeX

@misc{cryptoeprint:2020/590,
author = {Jun Wan and Hanshen Xiao and Elaine Shi and Srinivas Devadas},
title = {Expected Constant Round Byzantine Broadcast under Dishonest Majority},
howpublished = {Cryptology ePrint Archive, Paper 2020/590},
year = {2020},
note = {\url{https://eprint.iacr.org/2020/590}},
url = {https://eprint.iacr.org/2020/590}
}

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