Byzantine Fault Tolerance [BFT]
BFT is the property of a system that can resist the class of failures derived from the Byzantine Generals’ Problem, which is a logical dilemma that illustrates how a group of Byzantine generals may have communication problems when trying to agree on their next move. Thus, a BFT system can continue to operate even if some of the nodes fail or act maliciously.
A Byzantine fault (also Byzantine generals problem, interactive consistency, source congruency, error avalanche, Byzantine agreement problem, and Byzantine failure) is a condition of a computer system, particularly distributed computing systems, where components may fail and there is imperfect information on whether a component has failed. The term takes its name from an allegory, the "Byzantine generals problem", developed to describe a situation in which, in order to avoid catastrophic failure of the system, the system's actors must agree on a concerted strategy, but some of these actors are unreliable.
In a Byzantine fault, a component such as a server can inconsistently appear both failed and functioning to failure-detection systems, presenting different symptoms to different observers. It is difficult for the other components to declare it failed and shut it out of the network, because they need to first reach a consensus regarding which component has failed in the first place. Byzantine fault tolerance (BFT) is the resiliency of a fault-tolerant computer system to such conditions.
