A Secure Sequencer and Data Availability Committee for Rollups (Extended Version)

2025-09-08

AI Summary

Layer 2 rollups face security risks from centralized sequencers and data availability committees (DACs), undermining decentralization and scalability. Method: We propose an L1-contract-based arbitration mechanism employing a game-theoretic fraud proof, modeling batch submission and state rollback correctness as a two-player adversarial game; we design a lightweight, efficient, and easily verifiable domain-specific fraud proof tailored to DAC properties—outperforming generic alternatives. Using Lean4, we formally model and verify the consensus protocol, fraud proof, and game strategies, establishing rigorous completeness and safety guarantees. Contribution/Results: The system enables malicious behavior detection, automated evidence generation, and honest participant incentives, effectively constraining sequencer and DAC misbehavior. It achieves low on-chain gas overhead while significantly enhancing L2 security and decentralization.

Technology Category

• Reasoning under Uncertainty: Sequential Decision Making
• Multiagent Systems: Mechanism Design
• Game Theory and Economic Paradigms: Mechanism Design

Application Category

• Security and Privacy: Data transparency and provenance
• Semantics and Knowledge: Provenance, trust, security and privacy, and ethical issues in managing semantic data
• Systems and Infrastructure for Web, Mobile and WoT: Decentralized Web and Fediverse systems

Abstract

Blockchains face a scalability limitation, partly due to the throughput limitations of consensus protocols, especially when aiming to obtain a high degree of decentralization. Layer 2 Rollups (L2s) are a faster alternative to conventional blockchains. L2s perform most computations offchain using minimally blockchains (L1) under-the-hood to guarantee correctness. A sequencer is a service that receives offchain L2 transaction requests, batches these transactions, and commits compressed or hashed batches to L1. Using hashing needs less L1 space, which is beneficial for gas cost, but requires a data availability committee (DAC) service to translate hashes into their corresponding batches of transaction requests. The behavior of sequencers and DACs influence the evolution of the L2 blockchain, presenting a potential security threat and delaying L2 adoption. We propose in this paper fraud-proof mechanisms, arbitrated by L1 contracts, to detect and generate evidence of dishonest behavior of the sequencer and DAC. We study how these fraud-proofs limit the power of adversaries that control different number of sequencer and DACs members, and provide incentives for their honest behavior. We designed these fraud-proof mechanisms as two player games. Unlike the generic fraud-proofs in current L2s (designed to guarantee the correct execution of transactions), our fraud-proofs are over pred-etermined algorithms that verify the properties that determine the correctness of the DAC. Arbitrating over concrete algorithms makes our fraud-proofs more efficient, easier to understand, and simpler to prove correct. We provide as an artifact a mechanization in LEAN4 of our fraud-proof games, including (1) the verified strategies that honest players should play to win all games as well as (2) mechanisms to detect dishonest claims.

Problem

• Detecting dishonest behavior in rollup sequencers
• Securing data availability committees against adversaries
• Designing efficient fraud-proof mechanisms for L2s

Innovation

• Fraud-proof mechanisms arbitrated by L1 contracts
• Two-player game design for efficient verification
• LEAN4 mechanization of fraud-proof games