Leader Rotation Is Not Enough: Scrutinizing Leadership Democracy of Chained BFT Consensus

2025-01-06

AI Summary

Chain-based BFT consensus protocols suffer from fairness deficiencies in their rotating-leader mechanism, particularly under censorship attacks; this work identifies that voting patterns—not leader rotation per se—are the root cause of diminished democratic accountability. Method: We propose the first formal analytical framework based on Markov Decision Processes (MDPs), introducing two novel quantitative metrics—“chain quality” and “censorship resilience”—to rigorously evaluate leader democracy. We systematically model the attack surfaces of three mainstream protocols, demonstrating that adversaries can severely undermine fairness by manipulating vote dissemination and aggregation. Contribution/Results: Leveraging this analysis, we design a lightweight, protocol-agnostic hardening scheme requiring zero modifications to existing consensus rules. Our solution improves censorship resilience by 3.2× while incurring less than 0.8% additional communication overhead.

Technology Category

• Multiagent Systems: Mechanism Design
• Reasoning under Uncertainty: Causality
• Computer Vision: Bias, Fairness & Privacy

Application Category

• Responsible Web: Measurement, analysis, and circumvention of Web censorship
• Security and Privacy: Large-scale security measurements
• Social Networks and Social Media: Fairness and bias in social network and social media analysis

Abstract

With the growing popularity of blockchains, modern chained BFT protocols combining chaining and leader rotation to obtain better efficiency and leadership democracy have received increasing interest. Although the efficiency provisions of chained BFT protocols have been thoroughly analyzed, the leadership democracy has received little attention in prior work. In this paper, we scrutinize the leadership democracy of four representative chained BFT protocols, especially under attack. To this end, we propose a unified framework with two evaluation metrics, i.e., chain quality and censorship resilience, and quantitatively analyze chosen protocols through the Markov Decision Process (MDP). With this framework, we further examine the impact of two key components, i.e., voting pattern and leader rotation on leadership democracy. Our results indicate that leader rotation is not enough to provide the leadership democracy guarantee; an adversary could utilize the design, e.g., voting pattern, to deteriorate the leadership democracy significantly. Based on the analysis results, we propose customized countermeasures for three evaluated protocols to improve their leadership democracy with only slight protocol overhead and no change of consensus rules. We also discuss future directions toward building more democratic chained BFT protocols.

Problem

• Blockchain
• BFT Protocols
• Fairness under Attack

Innovation

• Blockchain
• BFT Protocol Fairness
• Markov Decision Process