Towards a Formal Foundation for Blockchain Rollups

TL;DR

This paper provides a formal analysis of blockchain Layer 2 solutions, specifically Rollups, using Alloy specifications to improve security, censorship resistance, and design correctness.

Contribution

It introduces a formal modeling approach for Layer 2 functionalities, identifies design pitfalls, and proposes a comprehensive methodology for security analysis of rollups.

Findings

Identified vulnerabilities in existing Layer 2 designs.

Developed a correct, model-checked Layer 2 model.

Proposed a new methodology for security and censorship resistance analysis.

Abstract

Blockchains like Bitcoin and Ethereum have revolutionized digital transactions, yet scalability issues persist. Layer 2 solutions, such as validity proof Rollups (ZK-Rollups), aim to address these challenges by processing transactions off-chain and validating them on the main chain. However, concerns remain about security and censorship resistance, particularly regarding centralized control in Layer 2 and inadequate mechanisms for enforcing these properties through Layer 1 smart contracts. In their current form, L2s are susceptible to multisig attacks that can lead to total user funds loss. This work presents a formal analysis using the Alloy specification language to examine and design key Layer 2 functionalities, including forced transaction queues, safe blacklisting, and upgradeability. Through this analysis, we identify pitfalls in existing designs and introduce an enhanced model that has been model-checked to be correct. Finally, we propose a complete end-to-end methodology to analyze rollups' security and censorship resistance based on manually translating Alloy properties to property-based testing invariants, setting new standards.