Pako: Multi-Valued Byzantine Agreement Comparable to Partially-Synchronous BFT

Abstract

Asynchronous Byzantine Fault Tolerance (BFT) consensus protocols are gaining attention for their resilience against network attacks. Among them, Multi-valued Byzantine Agreement (MVBA) protocols play a critical role, which accepts input values from each replica and returns a consistent output. The state-of-the-art MVBA protocol, sMVBA, has a good-case latency of $6\delta$ and an expected bad-case latency of $12\delta$, with $\delta$ representing the network delay. Additionally, sMVBA exhibits a communication of $O(n^{2})$ in both good and bad cases. Although it outperforms other MVBA protocols, sMVBA still lags behind partially-synchronous counterparts. For instance, PBFT achieves a good-case latency of $3\delta$, and HotStuff boasts a good-case communication of $O(n)$. This paper introduces a novel MVBA protocol, Pako, aiming for performance comparable to partially-synchronous protocols. Pako leverages an existing MVBA protocol as a black box and introduces an additional view with an optimistic path to commit values efficiently. Two Pako variants, Pako1 and Pako2, provide a trade-off between latency and communication. To be more specific, Pako1 achieves a good-case latency of $3\delta$ with $O(n^{2})$ communication, while Pako2 reduces the communication to $O(n)$ with a slightly higher good-case latency of $5\delta$. A series of experiments demonstrate Pako's significant outperformance of counterparts.