The Hermes BFT for Blockchains

TL;DR

Hermes is a BFT consensus protocol that reduces primary node dependency and improves performance in blockchain networks, especially with bandwidth-limited nodes, by relaxing safety guarantees for certain Byzantine faults.

Contribution

Hermes introduces a novel approach to BFT consensus that minimizes primary node influence and enhances throughput and latency in the presence of slack nodes.

Findings

Hermes achieves over 4x throughput improvement with slack nodes.

Hermes reduces latency by up to 15x compared to state-of-the-art protocols.

Performance is comparable to existing protocols without slack nodes.

Abstract

The performance of partially synchronous BFT-based consensus protocols is highly dependent on the primary node. All participant nodes in the network are blocked until they receive a proposal from the primary node to begin the consensus process.Therefore, an honest but slack node (with limited bandwidth) can adversely affect the performance when selected as primary. Hermes decreases protocol dependency on the primary node and minimizes transmission delay induced by the slack primary while keeping low message complexity and latency. Hermes achieves these performance improvements by relaxing strong BFT agreement (safety) guarantees only for a specific type of Byzantine faults (also called equivocated faults). Interestingly, we show that in Hermes equivocating by a Byzantine primary is unlikely, expensive and ineffective. Therefore, the safety of Hermes is comparable to the general BFT consensus. We deployed and tested Hermes on 190 Amazon EC2 instances. In these tests, Hermes's performance was comparable to the state-of-the-art BFT protocol for blockchains (when the network size is large) in the absence of slack nodes. Whereas, in the presence of slack nodes Hermes out performed the state-of-the-art BFT protocol by more than 4x in terms of throughput as well as 15x in terms of latency.