Synchronous Byzantine Agreement with Expected O(1) Rounds, Expected O(n2) Communication, and Optimal Resilience.

We present new protocols for Byzantine agreement in the synchronous and authenticated setting, tolerating the optimal number of f faults among n = 2f + 1 parties. Our protocols achieve an expected O(1) round complexity and an expected O(n(2)) communication complexity. The exact round complexity in expectation is 10 for a static adversary and 16 for a strongly rushing adaptive adversary. For comparison, previous protocols in the same setting require expected 29 rounds.