Troxy: Transparent Access to Byzantine Fault-Tolerant Systems

Various protocols and architectures have been proposed to make Byzantine fault tolerance (BFT) increasingly practical. However, the deployment of such systems requires dedicated client-side functionality. This is necessary as clients have to connect to multiple replicas and perform majority voting over the received replies to outvote faulty responses. Deploying custom client-side code is cumbersome, and often not an option, especially in open heterogeneous systems and for well-established protocols (e.g., HTTP and IMAP) where diverse client-side implementations co-exist. We propose Troxy, a system which relocates the BFT-specific client-side functionality to the server side, thereby making BFT transparent to legacy clients. To achieve this, Troxy relies on a trusted subsystem built upon hardware protection enabled by Intel SGX. Additionally, Troxy reduces the replication cost of BFT for read-heavy workloads by offering an actively maintained cache that supports trustworthy read operations while preserving the consistency guarantees offered by the underlying BFT protocol. A prototype of Troxy has been built and evaluated, and results indicate that using Troxy (1) leads to at most 43% performance loss with small ordered messages in a local network environment, while (2) improves throughput by 130% with read-heavy workloads in a simulated wide-area network.