Bachelor/Master Thesis
Beyond Worst-Case Analysis of Simplex Consensus: A Simulation Study
Simplex consensus [1] is a recent Byzantine fault-tolerant (BFT) protocol that aims to be simple to describe and analyze, while matching or improving the efficiency of recent state-of-the-art protocols. In each iteration, a leader proposes a block, validators vote either for that block or, after a timeout, for a dummy block, and successful notarization is followed by a separate finalize step. In good executions, this yields very low latency, while under adverse timing the protocol may fall back to dummy-block votes and delayed progress. Simplex is also revisited in Sing a Song of Simplex [2], which discusses optimizations and may serve as a more accessible companion to the original paper. This makes Simplex a good case study for an important systems question: beyond best-case and worst-case analysis, how does the protocol behave in realistic scenarios.
This project studies the performance robustness of Simplex under adversarial timing behavior in a configurable simulator. The student will implement the protocol, model attacks such as a slow proposer, targeted message delays, and proposer crashes, and measure how these behaviors affect finalization latency, failed or delayed iterations, dummy-block fallbacks, throughput degradation, and recovery once the attack stops. The goal is to understand which adversarial conditions Simplex is most sensitive to, how severe their impact is, and how the protocol behaves in practice as timing faults become progressively more disruptive.
For a Master’s thesis, the project extends the study to Tendermint [3], a widely known partially synchronous BFT protocol based on propose, prevote, and precommit rounds with locking. A central challenge will be to define a fair comparison methodology with a common adversarial budget across both protocols despite their different control flows and timeout behavior. The outcome should be a comparative analysis of how Simplex and Tendermint react to timing-based attacks, how quickly they recover after failed rounds, and whether Simplex’s simpler structure leads to a different robustness profile in practice.
References
[1] Benjamin Y. Chan and Rafael Pass. Simplex Consensus: A Simple and Fast Consensus Protocol. Theory of Cryptography Conference (TCC 2023). Also at IACR ePrint 2023/463. (talk from Benjamin Chan)