State machine replication is a common approach for making a distributed service highly available and resilient to failures, by replicating it on different processes. It is well-known, however that the difficulty of ensuring the safety and liveness of a replicated service increases significantly when no synchrony assumptions are made, and when processes can exhibit Byzantine behaviors. The contribution of this work is to break the complexity of devising a Byzantine-resilient state machine replication protocol, by decomposing it into key modular abstractions. In addition to being modular the protocol we propose always preserves safety in presence of less than one third of Byzantine processes, independently of any synchrony assumptions. As for the liveness of our protocol, it relies on a Byzantine failure detector that encapsulates the sufficient amount of synchrony.