Logo
ScienceStack
Table of Contents
Fetching ...
Sign In

A Security Framework for General Blockchain Layer 2 Protocols

Zeta Avarikioti, Matteo Maffei, Yuheng Wang

TL;DR

We address the lack of a general, composable security framework for Layer 2 blockchain protocols by introducing an iUC-based ideal functionality for Layer 2, along with modular subroutines that cover joining, submitting, updating, reading, and settlement. By instantiating this framework with Brick, Liquid, and Arbitrum Nitro, the work demonstrates how diverse L2 designs can be analyzed under common security and efficiency criteria, including safety, liveness, and data-availability. The formalism enables rigorous, protocol-agnostic reasoning and reveals intrinsic trade-offs between safety, liveness, and data availability across paradigms. It lays groundwork for secure and incentive-aware L2 design and supports extensions to cross-chain and multi-hop L2 compositions.

Abstract

Layer 2 (L2) solutions are the cornerstone of blockchain scalability, enabling high-throughput and low-cost interactions by shifting execution off-chain while maintaining security through interactions with the underlying ledger. Despite their common goals, the principal L2 paradigms -- payment channels, rollups, and sidechains -- differ substantially in architecture and assumptions, making it difficult to comparatively analyze their security and trade-offs. To address this, we present the first general security framework for L2 protocols. Our framework is based on the IITM-based Universal Composability (iUC) framework, in which L2 protocols are modeled as stateful machines interacting with higher-level protocol users and the underlying ledger. The methodology defines a generic execution environment that captures ledger events, message passing, and adversarial scheduling, and characterizes security through trace-based predicates parameterized by adversarial capabilities and timing assumptions. By abstracting away from protocol-specific details while preserving critical interface and execution behavior, the framework enables modular, protocol-agnostic reasoning and composable security proofs across a wide range of L2 constructions. To demonstrate its applicability, we analyze an example from each of the three dominant L2 scaling paradigms: a payment channel (Brick), a sidechain (Liquid Network), and a rollup (Arbitrum). By instantiating each within our framework, we derive their security properties and expose trade-offs. These include the time for dispute resolution, distribution of off-chain storage and computation, and varying trust assumptions (e.g., reliance on honest parties or data availability). Our framework unifies the analysis of diverse L2 designs and pinpoints their strengths and limitations, providing a foundation for secure, systematic L2 development.

A Security Framework for General Blockchain Layer 2 Protocols

TL;DR

We address the lack of a general, composable security framework for Layer 2 blockchain protocols by introducing an iUC-based ideal functionality for Layer 2, along with modular subroutines that cover joining, submitting, updating, reading, and settlement. By instantiating this framework with Brick, Liquid, and Arbitrum Nitro, the work demonstrates how diverse L2 designs can be analyzed under common security and efficiency criteria, including safety, liveness, and data-availability. The formalism enables rigorous, protocol-agnostic reasoning and reveals intrinsic trade-offs between safety, liveness, and data availability across paradigms. It lays groundwork for secure and incentive-aware L2 design and supports extensions to cross-chain and multi-hop L2 compositions.

Abstract

Layer 2 (L2) solutions are the cornerstone of blockchain scalability, enabling high-throughput and low-cost interactions by shifting execution off-chain while maintaining security through interactions with the underlying ledger. Despite their common goals, the principal L2 paradigms -- payment channels, rollups, and sidechains -- differ substantially in architecture and assumptions, making it difficult to comparatively analyze their security and trade-offs. To address this, we present the first general security framework for L2 protocols. Our framework is based on the IITM-based Universal Composability (iUC) framework, in which L2 protocols are modeled as stateful machines interacting with higher-level protocol users and the underlying ledger. The methodology defines a generic execution environment that captures ledger events, message passing, and adversarial scheduling, and characterizes security through trace-based predicates parameterized by adversarial capabilities and timing assumptions. By abstracting away from protocol-specific details while preserving critical interface and execution behavior, the framework enables modular, protocol-agnostic reasoning and composable security proofs across a wide range of L2 constructions. To demonstrate its applicability, we analyze an example from each of the three dominant L2 scaling paradigms: a payment channel (Brick), a sidechain (Liquid Network), and a rollup (Arbitrum). By instantiating each within our framework, we derive their security properties and expose trade-offs. These include the time for dispute resolution, distribution of off-chain storage and computation, and varying trust assumptions (e.g., reliance on honest parties or data availability). Our framework unifies the analysis of diverse L2 designs and pinpoints their strengths and limitations, providing a foundation for secure, systematic L2 development.

Paper Structure

This paper contains 65 sections, 32 theorems, 6 figures, 2 tables.

Table of Contents

  1. Introduction
  2. Model
  3. The Ideal Functionality for L2 Protocols
  4. Description of $\mathcal{F}_{\text{layer2}}$ and subroutines
  5. Security Properties
  6. Efficiency Property
  7. Case Studies in L2 Protocols
  8. Case Study: The Brick Channel
  9. The Real Brick Protocol $\mathcal{P}^{\text{Brick}}$
  10. The Ideal Functionality $\mathcal{F}^{\text{Brick}}_{\text{layer2}}$
  11. Case Study: The Liquid Network Sidechain
  12. The Real Liquid Network Protocol $\mathcal{P}^{\text{Liquid}}$.
  13. The Ideal Functionality $\mathcal{F}^{\text{Liquid}}_{\text{layer2}}$
  14. Case Study: The Arbitrum Nitro Rollup
  15. The Real Arbitrum Nitro Protocol $\mathcal{P}^{\text{Arbitrum}}$.
  16. ...and 50 more sections

Key Result

theorem 1

The ideal functionality $\mathcal{F}^{\text{Brick}}_{\text{layer2}}$ guarantees all the security properties of a secure L2 protocol.

Figures (6)

  • Figure 1: Structure of the ideal functionality $\mathcal{F}^{\Lambda}_{\text{layer2}}$ for a secure L2 protocol $\Lambda$. $\mathcal{E}$ refer to the environment, $\mathcal{S}$ refer to the simulator and $\mathcal{A}$ refer to the adversary.
  • Figure 2: The ideal functionality $\mathcal{F}_{\text{layer2}}$'s main logic for handling the requests. pidcur is the current party and sidcur the L2 protocol’s current session.
  • Figure 3: The Brick payment channel protocol
  • Figure 4: The Liquid Network sidechain protocol
  • Figure 5: The Arbitrum protocol
  • ...and 1 more figures

Theorems & Definitions (41)

  • definition 1: Correct Initialization
  • definition 2: $f$-safety
  • definition 3: {$f$,$T$}-liveness for request
  • definition 4: correct settlement
  • definition 5
  • definition 6: ($G_{L_2}$, $G_{L_1}$)-Data Availability
  • theorem 1
  • theorem 2
  • theorem 3
  • theorem 4
  • ...and 31 more