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Byzantine Generals’ Problem
A situation where communication that requires consensus on a single strategy from all members within a group or party cannot be trusted or verified.
What Is the Byzantine Generals’ Problem?
The Byzantine Generals’ Problem is a thought experiment that deals with a key question of computer science: is it possible to form a consensus in a computer network composed of independent, geographically distributed nodes?
The problem was proposed in 1982 by researchers from the SRI International Research Institute.
It goes as follows: there are a number of Byzantine generals besieging a city. They can only communicate via sending messengers to each other. The generals must agree on a common plan of action: whether to attack the city or retreat. However, some of the generals are traitorous and actively working against the forming of a consensus; their number and identities are unknown.
The question posed by the problem is what decision-making algorithm the generals should use to devise a common plan — regardless of the traitors’ interference — and whether such an algorithm exists at all.
According to the researchers’ own analysis, such a system is indeed feasible, but the number of loyal generals must strictly exceed two-thirds. For example, in a situation with three generals, one of which is traitorous, the loyal ones can never guarantee that they will be able to reach a consensus.