Cryptology ePrint Archive: Report 2019/1128

SoK: Communication Across Distributed Ledgers

Alexei Zamyatin and Mustafa Al-Bassam and Dionysis Zindros and Eleftherios Kokoris-Kogias and Pedro Moreno-Sanchez and Aggelos Kiayias and William J. Knottenbelt

Abstract: Since the inception of Bitcoin, a plethora of distributed ledgers differing in design and purpose has been created. While by design, blockchains provide no means to securely communicate with external systems, numerous attempts towards trustless cross-chain communication have been proposed over the years. Today, cross-chain communication (CCC) plays a fundamental role in cryptocurrency exchanges, scalability efforts via sharding, extension of existing systems through sidechains, and bootstrapping of new blockchains. Unfortunately, existing proposals are designed ad-hoc for specific use-cases, making it hard to gain confidence in their correctness and composability.

We provide the first systematic exposition of cross-chain communication protocols. We formalize the underlying research problem and show that CCC is impossible without a trusted third party, contrary to common beliefs in the blockchain community. With this result in mind, we develop a framework to design new and evaluate existing CCC protocols, focusing on the inherent trust assumptions thereof, and derive a classification covering the field of cross-chain communication to date. We conclude by discussing open challenges for CCC research and the implications of interoperability on the security and privacy of blockchains.

Category / Keywords: cryptographic protocols / blockchains, distributed ledgers, interoperability, cross-chain communication

Original Publication (with major differences): Financial Cryptography and Data Security 2021

Date: received 1 Oct 2019, last revised 5 Feb 2021

Contact author: azamyatin at imperial ac uk

Available format(s): PDF | BibTeX Citation

Note: Updated evaluation with latest cross-chain research papers. Extended discussion on challenges and future research directions.

Version: 20210205:181453 (All versions of this report)

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