LibraBFT

LibraBFT is a Byzantine fault-tolerant consensus protocol developed for the Libra blockchain project by Facebook’s Libra initiative. It provides agreement among validator nodes on the order and inclusion of transactions into a shared ledger, enabling safe operation of a permissioned blockchain.

The protocol is leader-based and designed for partial synchrony. It uses threshold signatures to produce Quorum Certificates (QCs) that certify blocks. The validator set is assumed to be of size n with up to f faulty nodes, where n = 3f + 1. In LibraBFT, a block proposal is created by a designated leader in a view. Validators vote on the proposal, and sufficent votes produce a QC. Blocks certified with QCs are chained, and a block becomes committed when there exists a descendant with a QC on its head, providing safety even in the presence of some network delays. A view-change mechanism rotates the leader when progress stalls.

LibraBFT was designed to support fast confirmation and resilience to delays, with mechanisms for reconfiguration to accommodate validator-set changes and updates to the network. It served as the core consensus for the Libra blockchain, which later evolved into the Diem project, and it influenced subsequent iterations of the network’s consensus approach.

Key properties of LibraBFT include safety—no two honest nodes disagree about committed history—under up to f Byzantine validators, and liveness under suitable synchrony assumptions. The protocol emphasizes cryptographic aggregation of validator votes into compact certificates and a clear leader-based progression to reach consensus efficiently in a permissioned setting.