In this problem, a group of army generals who lead different parts of
the Byzantine army is planning to attack or retreat from a city. The only
way of communicating among them is via a messenger. They need to
agree to strike at the same time in order to win. The issue is that one or
more generals might be traitors who could send a misleading message.
Therefore, there is a need for a viable mechanism that allows for
agreement among the generals, even in the presence of the treacherous
ones, so that the attack can still take place at the same time. As an analogy
for distributed systems, the generals can be considered honest nodes, the
traitors as Byzantine nodes (that is, nodes with arbitrary behavior), and
the messenger can be thought of as a channel of communication among
the generals.
This problem was solved in 1999 by Castro and Liskov who presented the
Practical Byzantine Fault Tolerance (PBFT) algorithm, which solves the
consensus problem in the presence of Byzantine faults in asynchronous
networks by utilizing the state machine replication protocol. PBFT goes
through a number of rounds to eventually reach an agreement between
nodes on the proposed value
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