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Atomicity and Abstraction for Cross-Blockchain Interactions

Huaixi Lu, Akshay Jajoo, Kedar S. Namjoshi

TL;DR

This work tackles the lack of portable abstractions for cross-blockchain programming by introducing a uniform inter-blockchain communication interface and a general atomicity protocol for multi-chain transactions. The approach, inspired by two-phase commit, provides formal correctness and trustworthiness under clear bridge assumptions and is instantiated over LayerZero and IBC with a Solidity prototype. The authors demonstrate practicality through implementations of pairwise and multi-chain exchanges on testnets, showing comparable performance to bespoke solutions and manageable gas costs. The result is a scalable framework that simplifies building reliable multi-chain applications and sets the stage for further optimizations in cross-chain communication and coordination.

Abstract

A blockchain facilitates secure and atomic transactions between mutually untrusting parties on that chain. Today, there are multiple blockchains with differing interfaces and security properties. Programming in this multi-blockchain world is hindered by the lack of general and convenient abstractions for cross-chain communication and computation. Current cross-chain communication bridges have varied and low-level interfaces, making it difficult to develop portable applications. Current methods for multi-chain atomic transactions are limited in scope to cryptocurrency swaps. This work addresses these issues. We first define a uniform, high-level interface for communication between chains. Building on this interface, we formulate a protocol that guarantees atomicity for general transactions whose operations may span several chains. We formulate and prove the desired correctness and security properties of these protocols. Our prototype implementation is built using the LayerZero cross-chain bridge. Experience with this implementation shows that the new abstractions considerably simplify the design and implementation of multi-chain transactions. Experimental evaluation with multi-chain swap transactions demonstrates performance comparable to that of custom-built implementations.

Atomicity and Abstraction for Cross-Blockchain Interactions

TL;DR

This work tackles the lack of portable abstractions for cross-blockchain programming by introducing a uniform inter-blockchain communication interface and a general atomicity protocol for multi-chain transactions. The approach, inspired by two-phase commit, provides formal correctness and trustworthiness under clear bridge assumptions and is instantiated over LayerZero and IBC with a Solidity prototype. The authors demonstrate practicality through implementations of pairwise and multi-chain exchanges on testnets, showing comparable performance to bespoke solutions and manageable gas costs. The result is a scalable framework that simplifies building reliable multi-chain applications and sets the stage for further optimizations in cross-chain communication and coordination.

Abstract

A blockchain facilitates secure and atomic transactions between mutually untrusting parties on that chain. Today, there are multiple blockchains with differing interfaces and security properties. Programming in this multi-blockchain world is hindered by the lack of general and convenient abstractions for cross-chain communication and computation. Current cross-chain communication bridges have varied and low-level interfaces, making it difficult to develop portable applications. Current methods for multi-chain atomic transactions are limited in scope to cryptocurrency swaps. This work addresses these issues. We first define a uniform, high-level interface for communication between chains. Building on this interface, we formulate a protocol that guarantees atomicity for general transactions whose operations may span several chains. We formulate and prove the desired correctness and security properties of these protocols. Our prototype implementation is built using the LayerZero cross-chain bridge. Experience with this implementation shows that the new abstractions considerably simplify the design and implementation of multi-chain transactions. Experimental evaluation with multi-chain swap transactions demonstrates performance comparable to that of custom-built implementations.
Paper Structure (25 sections, 3 theorems, 1 equation, 7 figures, 3 tables)

This paper contains 25 sections, 3 theorems, 1 equation, 7 figures, 3 tables.

Table of Contents

  1. Introduction
  2. Background
  3. Blockchain Interoperability
  4. Cross-Chain Bridges
  5. Atomicity for Multi-chain Applications
  6. Threat Model
  7. An Abstract Communication Interface
  8. Notify with acknowledgement
  9. Remote Call
  10. An Atomic Multi-Chain Transaction Protocol
  11. Cross-Chain Transactions
  12. Atomicity
  13. Blockchain Assumptions
  14. The Atomicity Protocol
  15. Protocol Stages
  16. ...and 10 more sections

Key Result

Theorem 1

The protocol ensures that notifications cannot be forged (safety) and are eventually delivered (liveness).

Figures (7)

  • Figure 1: The communication flow through a CCC bridge
  • Figure 2: A Combined Flow Diagram for the Notify-with-Acknowledgement/Remote Call Protocol.
  • Figure 3: The ideal execution for a cross-chain transaction
  • Figure 4: Sketch (pseudo-code) for the lock, unlock, and guarded regular methods of a contract.
  • Figure 5: Overview of the two phase commit protocol.
  • ...and 2 more figures

Theorems & Definitions (4)

  • Definition 1: Secure Transfer
  • Theorem 1
  • Theorem 2
  • Theorem 3