On the Practicality of Practical Byzantine Fault Tolerance

Byzantine Fault Tolerant (BFT) systems are considered to be state of the art with regards to providing reliability in distributed systems. Despite over a decade of research, however, BFT systems are rarely used in practice. In this paper, we describe our experience, from an application developer's perspective, trying to leverage the publicly available, highly- studied and extended "PBFT" middleware (by Castro and Liskov), to provide provable reliability guarantees for an electronic voting application with high security and robustness needs. We describe several obstacles we encountered and drawbacks we identified in the PBFT approach. These include some that we tackled, such as lack of support for dynamic client management and leaving state management completely up to the application. Others still remaining include the lack of robust handling of non-determinism, lack of support for web-based applications, lack of support for stronger cryptographic primitives, and more. We find that, while many of the obstacles could be overcome, they require significant engineering effort and time and their performance implications for the end-application are unclear. An application developer is thus unlikely to be willing to invest the time and effort to do so to leverage the BFT approach.