Cryptology ePrint Archive: Report 2022/255

Round-Optimal Byzantine Agreement

Diana Ghinea and Vipul Goyal and Chen-Da Liu-Zhang

Abstract: Byzantine agreement is a fundamental primitive in cryptography and distributed computing, and minimizing its round complexity is of paramount importance. It is long known that any randomized $r$-round protocol must fail with probability at least $(c\cdot r)^{-r}$, for some constant $c$, when the number of corruptions is linear in the number of parties, $t = \theta(n)$. On the other hand, current protocols fail with probability at least $2^{-r}$. Whether we can match the lower bound agreement probability remains unknown.

In this work, we resolve this long-standing open question. We present a protocol that matches the lower bound up to constant factors. Our results hold under a (strongly rushing) adaptive adversary that can corrupt up to $t = (1-\epsilon)n/2$ parties, and our protocols use a public-key infrastructure and a trusted setup for unique threshold signatures. This is the first protocol that decreases the failure probability (overall) by a 'super-constant' factor per round.

Category / Keywords: cryptographic protocols / Byzantine agreement, optimal, round complexity

Original Publication (in the same form): IACR-EUROCRYPT-2022

Date: received 25 Feb 2022

Contact author: chendaliu at gmail com

Available format(s): PDF | BibTeX Citation

Version: 20220302:140029 (All versions of this report)

Short URL:

[ Cryptology ePrint archive ]