Brief Note: Fast Authenticated Byzantine Consensus

TL;DR

This paper introduces a new authenticated Byzantine fault-tolerant consensus protocol that achieves 2-round commit with fewer replicas than previous protocols, improving latency and resilience claims.

Contribution

It presents a 2-round BFT SMR protocol with fewer replicas, challenging prior optimality claims and optimizing for permissioned blockchain systems.

Findings

Achieves 2-round BFT consensus with n ≥ 5f-1 replicas.

For f=1, only 4 replicas are needed, reducing latency.

Refutes previous claims of optimal resiliency in similar protocols.

Abstract

Byzantine fault-tolerant (BFT) state machine replication (SMR) has been studied for over 30 years. Recently it has received more attention due to its application in permissioned blockchain systems. A sequence of research efforts focuses on improving the commit latency of the SMR protocol in the common good case, including PBFT with $3$-round latency and $n\geq 3f+1$ and FaB with $2$-round latency and $n\geq 5f+1$. In this paper, we propose an authenticated protocol that solves $2$-round BFT SMR with only $n\geq 5f-1$ replicas, which refutes the optimal resiliency claim made in FaB for needing $n \geq 5f+1$ for $2$-round PBFT-style BFT protocols. For the special case when $f=1$, our protocol needs only $4$ replicas, and strictly improves PBFT by reducing the latency by one round (even when one backup is faulty).