Byzantine Fault Tolerance

A distributed system immune to Byzantine Failures is described as having Byzantine Fault Tolerance. A distributed system is considered vulnerable to Byzantine Faults when components are faulty, yet the system cannot determine whether a given component is faulty. In the context of blockchain consensus systems, systems that are Byzantine Fault Tolerant can reach consensus even when a portion of the nodes are dishonest or dysfunctional, and the property is desired for its role in increasing network security. The term takes its name from the Byzantine Generals problem, first outlined by computer scientists Leslie Lamport in the 1980s, in which multiple generals endeavor to reach agreement via messages, knowing that some generals might be traitorous and send forged messages. The problem is a metaphor for multiple computers trying to reach consensus about the state of the system even if some computers are malicious or nonfunctioning.

Byzantine Fault Tolerance is not itself a consensus mechanism, like Proof of Work or Proof of Stake, but rather a property of distributed systems that many consensus mechanisms strive to enable.