What Is Byzantine Generals Problem?

The problem was defined in a 1982 paper published by Leslie Lamport, Robert Shostak and Marshall Pease. In the scenario, the generals of a Byzantine army besieging a city can communicate only through messengers and must jointly decide whether to attack or retreat. Some of the generals may be traitors and may send conflicting messages to different generals. The challenge is to ensure that the honest generals reach the same decision despite the traitors. The paper shows that this is possible if the number of traitors is less than one third of the total.

This analogy applies to all distributed systems that have no central authority. In a cryptocurrency network, thousands of independent nodes must agree on which transactions are valid and in what order they will be recorded; some nodes, meanwhile, may malfunction or try to deceive the network.

Bitcoin is considered the first system to offer a practical solution to this problem in a public and permissionless network, using the Proof of Work mechanism. By making block production costly and treating the chain with the most work as valid, it makes agreement possible as long as honest participants hold the majority of the computing power. Proof of Stake and BFT-derived algorithms bring different solutions to the same problem.