The HotStuff protocol is a recent breakthrough inByzantine Fault Tolerant (BFT) consensus that enjoys responsiveness and linear view change. It uses a clever three-chain commit rule to achieve responsiveness while the vast majority of BFT protocols are using the standard two-chain commit rule. This brings us to a fundamental question: Is a three-chain commit rule really necessary to achieve responsiveness? In this paper, we answer this question by designing a two-chain variant ofHotStuff called Fast-HotStuff that still enjoys responsiveness with simplified view change. Compared to the three-chain HotStuff, Fast-HotStuff has lower latency and is more resilient against forking attacks. Moreover, Fast-HotStuff can be combined with Proof-of-Stake (PoS) while still maintaining safety and liveness. In sharp contrast, HotStuff and its variant LibraBFT (which plans to use PoS) fail to have this property as malicious nodes can takeover the network. In order to achieve all of these advantages, Fast-HotStuff adds a small amount of overhead information during the block proposal phase, which is only needed if the previous primary node fails. The correctness of Fast-HotStuff is established in terms of safety and liveness. The effectiveness of Fast-HotStuff is demonstrated through experimental results.
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