Pako: Multi-valued Byzantine Agreement Comparable to Partially-synchronous BFT

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 6δ and an expected bad-case latency of 12δ, with δ 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 3δ, 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 3δ with O ( n 2 ) communication, while Pako2 reduces the communication to O ( n ) with a slightly higher good-case latency of 5δ. A series of experiments demonstrate Pako's significant outperformance of counterparts.