EFS: Efficient and Fault-Scalable Byzantine Fault Tolerant Systems Against Faulty Clients

Abstract

Byzantine fault tolerant (BFT) protocols enhance system safety and availability in asynchronous networks, despite the arbitrary faults at both servers and clients. A practical BFT system should be efficient in both contention-free and contending cases, and fault scalable (i.e., efficiently tolerating the increasing number of server faults). However, few existing BFT systems completely satisfy this robustness requirement of efficiency. In this paper, we propose EFS, the first BFT solution that provides good efficiency and fault-scalability, in various cases (i.e. faulty or not, contending or not). EFS is a hybrid BFT system consisting of an efficient and fault scalable quorum protocol for the contention-free case and a fast agreement protocol to resolve contention in a fault-scalable manner. More importantly, its server-directed mode switch does not rely on digital signature nor introduce any extra communication overhead. This lightweight switch counters the vulnerability in the existing hybrid BFT systems, where faulty clients can simply send contending requests to degrade the performance significantly. The experiment results on the EFS prototype demonstrate robust fault tolerance.