This article was first published on OntologyNetwork - Medium
Recently, Facebook’s cryptocurrency Libra published its whitepaper and open-sourced its testnet codes on GitHub. In its whitepaper, we can see that Libra uses LibraBFT, a Byzantine Fault Tolerance consensus protocol. Since this protocol is derived from another consensus protocol HotStuff, it will help us understand what LibraBFT is by learning how HotStuff works.
1. What is HotStuff
HotStuff is a leader-based Byzantine fault-tolerant replication protocol proposed by VMware Research in March 2018. Its pre-printed version has been revised five times and will be officially published at PODC 2019 (2019 Symposium on Principles of Distributed Computing). Similar to many consensus protocols, its network is assumed to be a reliable and secure peer-to-peer network and its communication model adopts the partial synchrony model, which means there exists in the network an upper bound on message transmission delay. This upper bound is either unknown to the nodes in the network, or all the nodes know the upper bound and follow it after a certain unknown point.
In this article, we will briefly explain how HotStuff works and break down how HowStuff achieves its goal by first introducing the PBFT consensus protocol.
2. What is PBFT
Generally speaking, the goal of consensus protocols is to reach an agreement on system state in the decentralized network so that all (honest) nodes can transition from one state to another.
Normally, PBFT uses two rounds of peer-to-peer message exchanges to achieve this goal.
When the leader broadcasts its proposed (legal) state transition request to other nodes, as an honest node in the system, it first needs to know that enough nodes have also received this state transition request, that is, it can confirm this request is valid. Based on this, it also needs to know that enough nodes also confirm that the state transition is valid, thus confirming there is a consensus among ...
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