Smallest Collusions Define Transaction Fee Mechanism Vulnerability → Research

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Briefing

Traditional transaction fee mechanisms in blockchains struggle with miner and user collusion, a challenge not fully addressed by standard auction theory. This paper introduces c-Side-Contract-Proof (c-SCP) mechanisms, demonstrating that if a mechanism is robust against a two-party collusion involving the miner and two users, it is inherently robust against any larger collusion. This simplifies the analysis of collusion resistance, focusing security efforts on smaller, more manageable collusive groups, thereby enhancing the design of economically secure blockchain protocols.

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Context

Blockchain transaction fee mechanisms, central to network operation, have historically faced challenges from miner and user collusion, a phenomenon often categorized under Maximal Extractable Value (MEV). Existing auction theory, while foundational, did not fully account for the unique dynamics of decentralized, permissionless environments where off-chain side contracts could undermine protocol integrity. The complexity of analyzing collusion across varying numbers of participants presented a significant theoretical hurdle for designing truly robust mechanisms.

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Analysis

The paper’s core contribution is the formalization and analysis of c-Side-Contract-Proof (c-SCP) mechanisms within the blockchain transaction fee context. A mechanism is c-SCP if it remains robust even when the miner colludes with up to ‘c’ users through a side contract. The breakthrough demonstrates that the class of 2-SCP mechanisms is equivalent to the class of c-SCP mechanisms for any c ≥ 2, assuming consistent tie-breaking.

This fundamentally differs from prior approaches by establishing that the critical threshold for collusion vulnerability is surprisingly low → a collusion involving the miner and just two users. If a mechanism can withstand this “small collusion,” it can withstand any larger one, simplifying the design and verification of collusion-resistant protocols.

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Parameters

Core Concept → c-Side-Contract-Proof Mechanisms
Key Authors → Yotam Gafni
Key Finding → 2-SCP mechanisms equal c-SCP for c≥2
Publication Date → October 6, 2025
Source → arXiv:2510.05986

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Outlook

This research provides a crucial theoretical lens for future development in blockchain mechanism design. By establishing that the vulnerability to collusion is effectively capped at a “small collusion” (miner + two users), it directs future research and development efforts towards rigorously securing protocols against these specific, minimal collusive groups. In 3-5 years, this foundational understanding could lead to the deployment of more resilient transaction fee mechanisms, significantly reducing the impact of MEV and fostering fairer, more predictable on-chain economic interactions. It also opens new avenues for exploring the practical implications of this equivalence in various blockchain architectures.

This paper fundamentally redefines the theoretical understanding of collusion resistance in blockchain transaction fee mechanisms, offering a critical simplification for future protocol design and security analysis.

Signal Acquired from → arXiv.org