Paper 2020/406

Hybrid-BFT: Optimistically Responsive Synchronous Consensus with Optimal Latency or Resilience

Atsuki Momose and Jason Paul Cruz and Yuichi Kaji

Abstract

The breakthrough of blockchain in many decentralized cryptocurrencies has reactivated studies on consensus under network synchrony, which has better security than a consensus under network asynchrony but has been considered to be impractical and only theoretical so far. One of the biggest concerns is the speed of transaction processing. To solve this concern, transactions can be processed responsively, i.e., without reliance on synchrony. Another approach is to minimize reliance on synchrony to achieve optimal synchronous latency. In this paper, we consider answering the question ”Can we achieve both responsiveness and optimal synchronous latency?”. To do this, we first show some theoretical possibilities and impossibilities in achieving both responsiveness and optimal synchronous latency, and then we present a practical blockchain or state machine replication protocol we call Hybrid-BFT. Hybrid-BFT can process transactions responsively under normal situation, i.e., small number of faults, while it can achieve optimal synchronous latency even under worst situation. Furthermore, Hybrid-BFT achieves responsive leader change, making it completely free from synchronous delay under normal situation.