Efficient Synchronous Byzantine Consensus
This work addresses the need for more efficient Byzantine fault-tolerant systems, such as in cryptocurrencies, by leveraging synchrony assumptions, though it is incremental as it builds on prior protocols like PBFT.
The paper tackles the problem of Byzantine consensus by improving fault tolerance thresholds and reducing round complexity in synchronous settings, achieving a threshold of n=2f+1 replicas and committing decisions in 3 rounds in the common case, with synchronous Byzantine agreement in expected 8 rounds compared to 24 previously.
We present new protocols for Byzantine state machine replication and Byzantine agreement in the synchronous and authenticated setting. The celebrated PBFT state machine replication protocol tolerates $f$ Byzantine faults in an asynchronous setting using $3f+1$ replicas, and has since been studied or deployed by numerous works. In this work, we improve the Byzantine fault tolerance threshold to $n=2f+1$ by utilizing a relaxed synchrony assumption. We present a synchronous state machine replication protocol that commits a decision every 3 rounds in the common case. The key challenge is to ensure quorum intersection at one honest replica. Our solution is to rely on the synchrony assumption to form a post-commit quorum of size $2f+1$, which intersects at $f+1$ replicas with any pre-commit quorums of size $f+1$. Our protocol also solves synchronous authenticated Byzantine agreement in expected 8 rounds. The best previous solution (Katz and Koo, 2006) requires expected 24 rounds. Our protocols may be applied to build Byzantine fault tolerant systems or improve cryptographic protocols such as cryptocurrencies when synchrony can be assumed.