Brief Note: Fast Authenticated Byzantine Consensus
This work provides an incremental improvement in efficiency for permissioned blockchain systems by reducing replica requirements and latency.
The paper tackles the problem of reducing commit latency in Byzantine fault-tolerant state machine replication for permissioned blockchains, achieving a 2-round protocol with only n ≥ 5f-1 replicas, which refutes prior claims that n ≥ 5f+1 was optimal for such protocols.
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).