What are Byzantine fault tolerance (BFTs)?

Byzantine fault tolerance (BFT)refers to a system’s ability to continue functioning correctly even when some of its components (nodes) fail or act maliciously. It is named after the Byzantine Generals’ Problem, a theoretical problem in computer science that describes how distributed systems can reach consensus despite unreliable participants.

Software Implemented Fault Tolorence was described in "SIFT: design and analysis of a fault-tolerant computer for aircraft control", a 1972 paper by Wensley, et.al.

A 1982 paper by Lamport et. al. renamed this problem "The Byzantine Generals Problem". The authors imagine that several divisions of the Byzantine army are camped outside an enemy city, each division commanded by a general. The generals must decide on a common plan of action: attack or retreat. The problem is that some generals may be traitors.

The loyal generals must have some way to guarantee that they all decide upon the same plan of action and that the traitors cannot cause them to adopt a bad plan.

In summary, the Byzantine Generals Problem is a game theory problem, which describes the difficulty decentralized parties have in arriving at consensus without relying on a trusted central party. In a network where no member can verify the identity of other members, how can members collectively agree on a certain truth?

Byzantine fault tolerance is a crucial concept for distributed systems, especially blockchains , ensuring they can reach consensus protocol even in the presence of malicious or faulty nodes. Different BFT mechanisms are used depending on the blockchains' needs.