Not eXactly Byzantine: Efficient and Resilient TEE-Based State Machine Replication

TL;DR

This paper introduces NxBFT, a novel TEE-based state machine replication protocol that balances efficiency and resilience under a 'Not eXactly Byzantine' model, achieving high throughput and robustness against crash faults.

Contribution

NxBFT is the first to implement a TEE-based, leaderless, graph-based consensus protocol optimized for the NxB operating model, addressing crash recovery issues in asynchronous environments.

Findings

NxBFT achieves the highest throughput across tested scenarios.

Performance of NxBFT remains stable under crash faults.

Compared to leader-based protocols, NxBFT's throughput is less impacted by faults.

Abstract

We propose, implement, and evaluate NxBFT, a resilient and efficient State Machine Replication protocol using Trusted Execution Environments (TEEs). NxBFT focuses on a "Not eXactly Byzantine" (NxB) operating model as a middle ground between crash and Byzantine fault tolerance. NxBFT's consensus layer is asynchronous, graph-based, leaderless, and optimized for the NxB operating model, enabling load-balancing of requests between replicas and, in fault-free cases, two network round trips between decisions. We identify fundamental issues with crash recovery due the use of TEEs in asynchrony that only can be circumvented by relying on synchrony for liveness. We provide a throughput-latency trade-off analysis of NxBFT, Chained-Damysus (rotating leader), and MinBFT (static leader) for up to 40 replicas and network round trip latencies up to 150 ms. NxBFT achieves the highest throughput in all scenarios. When small latencies are required, MinBFT and Damysus are at an advantage with Damysus benefiting from the NxB model in terms of throughput for small deployments. In contrast to leader-based approaches, NxBFT's performance is almost not impacted when actual crash faults occur.