Hybrids on Steroids: SGX-Based High Performance BFT.

With the advent of trusted execution environments provided by recent general purpose processors, a class of replication protocols has become more attractive than ever: Protocols based on a hybrid fault model are able to tolerate arbitrary faults yet reduce the costs significantly compared to their traditional Byzantine relatives by employing a small subsystem trusted to only fail by crashing. Unfortunately, existing proposals have their own price: We are not aware of any hybrid protocol that is backed by a comprehensive formal specification, complicating the reasoning about correctness and implications. Moreover, current protocols of that class have to be performed largely sequentially. Hence, they are not well-prepared for just the modern multi-core processors that bring their very own fault model to a broad audience. In this paper, we present Hybster, a new hybrid state-machine replication protocol that is highly parallelizable and specified formally. With over 1 million operations per second using only four cores, the evaluation of our Intel SGX-based prototype implementation shows that Hybster makes hybrid state-machine replication a viable option even for today's very demanding critical services.