Paper 2018/1028

Synchronous Byzantine Agreement with Expected $O(1)$ Rounds, Expected $O(n^2)$ Communication, and Optimal Resilience

Ittai Abraham and Srinivas Devadas and Danny Dolev and Kartik Nayak and Ling Ren

Abstract

We present new protocols for Byzantine agreement in the synchronous and authenticated setting, tolerating the optimal number of $f$ faults among $n=2f+1$ parties. Our protocols achieve an expected $O(1)$ round complexity and an expected $O(n^2)$ communication complexity. The exact round complexity in expectation is 10 for a static adversary and 16 for a strongly rushing adaptive adversary. For comparison, previous protocols in the same setting require expected 29 rounds and expected $\Omega(n^3)$ communication. We also give a lower bound showing that expected $\Omega(f^2)$ communication is necessary against a strongly rushing adaptive adversary.