Editing Byzantine Agreement (section)

==Properties==
A Byzantine Agreement protocol is formally defined to satisfy the criteria ''agreement'', ''validity'' and ''termination''. Agreement simply requires every non-faulty player to output the same bit. Validity excludes the trivial solution of always outputting a specific bit, by requiring that the agreement value is at least proposed once. Termination means that any protocol is required to eventually finish. Formally, Byzantine agreement is achieved if

*''Agreement'': Every non-faulty player outputs the same bit <math>d</math>.

*''Validity'': The agreement value <math>d</math> is proposed by at least one node, i.e. <math>d = b_i</math> for some node <math>i</math>.

*''Termination'': The protocol will eventually terminate.

In Byzantine Agreement, node failures are modelled as Byzantine Failures. In this failure model, the failed nodes are allowed to behave arbitrarily, including maliciously trying to prevent the non-faulty nodes from reaching agreement. In particular, failed nodes can collude together.