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The Byzantine Generals Problem has been known for a long time, but it's possible to achieve consensus with 50% fault tolerance in a synchronous network. This means that messages broadcasted by any honest node are guaranteed to be received by all other honest nodes within some known time period. But if you add even more assumptions, you can increase fault tolerance all the way to 99%. The following will be my attempt to describe and reformulate the algorithm in a simplified form. The algorithm is described by Leslie Lamport’s famous 1982 paper “The Byzantine Generalals Problem” (link here)