Proof-Carrying Fair Ordering: Asymmetric Verification for BFT via Incremental Graphs

2025-10-15

AI Summary

In Byzantine Fault Tolerant (BFT) consensus, malicious leaders can launch value-extraction attacks—e.g., front-running—by imposing unfair transaction ordering; existing fairness-aware ordering schemes (e.g., Themis) rely on symmetric redundant verification, incurring high overhead. Method: We propose AUTIG, a high-performance, pluggable fair ordering service. AUTIG introduces the first threshold-triggered, event-driven incremental graph (UTIG) maintenance mechanism to enable asymmetric verification between leaders and followers, eliminating redundant computation. It employs a decoupled pipelined architecture for parallelization and constructs a succinct fairness proof structure ensuring pairwise fairness and frontier completeness. Formal auditing of graph properties guarantees safety. Contribution/Results: Under partial synchrony, AUTIG strictly enforces γ-batch fairness while achieving substantial throughput gains and significantly reduced end-to-end latency.

Technology Category

• Multiagent Systems: Mechanism Design
• Data Mining & Knowledge Management: Representing, Reasoning, and Using Provenance, Trust
• Game Theory and Economic Paradigms: Fair Division

Application Category

• Security and Privacy: Data transparency and provenance
• User Modeling, Personalization and Recommendation: Fairness-aware retrieval and ranking
• Economics, Online Markets and Human Computation: Fairness and ethical considerations in crowd work and in human-in-the-loop AI systems

Abstract

Byzantine Fault-Tolerant (BFT) consensus protocols ensure agreement on transaction ordering despite malicious actors, but unconstrained ordering power enables sophisticated value extraction attacks like front running and sandwich attacks - a critical threat to blockchain systems. Order-fair consensus curbs adversarial value extraction by constraining how leaders may order transactions. While state-of-the-art protocols such as Themis attain strong guarantees through graph-based ordering, they ask every replica to re-run the leader's expensive ordering computation for validation - an inherently symmetric and redundant paradigm. We present AUTIG, a high-performance, pluggable order-fairness service that breaks this symmetry. Our key insight is that verifying a fair order does not require re-computing it. Instead, verification can be reduced to a stateless audit of succinct, verifiable assertions about the ordering graph's properties. AUTIG realizes this via an asymmetric architecture: the leader maintains a persistent Unconfirmed-Transaction Incremental Graph (UTIG) to amortize graph construction across rounds and emits a structured proof of fairness with each proposal; followers validate the proof without maintaining historical state. AUTIG introduces three critical innovations: (i) incremental graph maintenance driven by threshold-crossing events and state changes; (ii) a decoupled pipeline that overlaps leader-side collection/update/extraction with follower-side stateless verification; and (iii) a proof design covering all internal pairs in the finalized prefix plus a frontier completeness check to rule out hidden external dependencies. We implement AUTIG and evaluate it against symmetric graph-based baselines under partial synchrony. Experiments show higher throughput and lower end-to-end latency while preserving gamma-batch-order-fairness.

Problem

• Preventing adversarial value extraction attacks in BFT consensus protocols
• Eliminating redundant computation in graph-based fair ordering verification
• Asymmetric verification of transaction fairness without historical state maintenance

Innovation

• Asymmetric verification reduces redundant computation workload
• Incremental graph maintenance amortizes construction across rounds
• Stateless audit with verifiable assertions ensures fairness proof