Make Every Word Count: Adaptive BA with Fewer Words

TL;DR

This paper introduces new Byzantine Agreement algorithms that adapt to actual failure counts, significantly reducing communication costs in common scenarios compared to worst-case bounds.

Contribution

It presents the first Byzantine Broadcast algorithm with $O(n(f+1))$ complexity and an optimal-resilience Byzantine Agreement algorithm with linear complexity in failure-free runs.

Findings

Byzantine Broadcast with $O(n(f+1))$ communication complexity.

Optimal-resilience Byzantine Agreement with linear complexity in failure-free cases.

Quadratic complexity in worst-case runs is maintained for general Byzantine Agreement.

Abstract

Byzantine Agreement is a key component in many distributed systems. While Dolev and Reischuk have proven a long time ago that quadratic communication complexity is necessary for worst-case runs, the question of what can be done in practically common runs with fewer failures remained open. In this paper we present the first Byzantine Broadcast algorithm with $O(n(f+1))$ communication complexity, where $0\leq f\leq t$ is the actual number of process failures in a run. And for BA with strong unanimity, we present the first optimal-resilience algorithm that has linear communication complexity in the failure-free case and a quadratic cost otherwise.