International Association
for Cryptologic Research

It is well-known that Asynchronous Total Order Broadcast (ATOB) requires randomisation and that at most $t < n/3$ out of $n$ players are corrupted. This is opposed to synchronous total-order broadcast (STOB) which can tolerate $t < n/2$ corruptions and can be deterministic. We show that these requirements can be conceptually separated, by constructing an ATOB protocol which tolerates $t < n/2$ corruptions from blackbox use of Common Coin and Reliable Broadcast. We show the power of this conceptually simple contribution by reproving, using simpler protocols, existing results on STOB with optimistic responsiveness and asynchronous fallback. We also use the framework to prove the first ATOB with sub-quadratic communication and optimal corruption threshold $t < n/3$, new ATOBs with covert security and mixed adversary structures, and a new STOB with asymmetric synchrony assumptions.