conference paper published yes Alexei Zamyatin author Mustafa Al-Bassam author Dionysis Zindros author Eleftherios Kokoris Kogias author f5983044-d7ef-11ea-ac6d-fd1430a26d30 Pedro Moreno-Sanchez author Aggelos Kiayias author William J. Knottenbelt author ElKo department FC: Financial Cryptography 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. Springer Nature2021Virtual eng 0302-9743 1611-3349 9-783-6626-4330-3 00071201620000110.1007/978-3-662-64331-0_1 12675 3-36 A. Zamyatin, M. Al-Bassam, D. Zindros, E. Kokoris Kogias, P. Moreno-Sanchez, A. Kiayias, W.J. Knottenbelt, in:, 25th International Conference on Financial Cryptography and Data Security, Springer Nature, 2021, pp. 3–36. Zamyatin, A., Al-Bassam, M., Zindros, D., Kokoris Kogias, E., Moreno-Sanchez, P., Kiayias, A., &#38; Knottenbelt, W. J. (2021). SoK: Communication across distributed ledgers. In <i>25th International Conference on Financial Cryptography and Data Security</i> (Vol. 12675, pp. 3–36). Virtual: Springer Nature. <a href="https://doi.org/10.1007/978-3-662-64331-0_1">https://doi.org/10.1007/978-3-662-64331-0_1</a> A. Zamyatin <i>et al.</i>, “SoK: Communication across distributed ledgers,” in <i>25th International Conference on Financial Cryptography and Data Security</i>, Virtual, 2021, vol. 12675, pp. 3–36. Zamyatin A, Al-Bassam M, Zindros D, Kokoris Kogias E, Moreno-Sanchez P, Kiayias A, Knottenbelt WJ. 2021. SoK: Communication across distributed ledgers. 25th International Conference on Financial Cryptography and Data Security. FC: Financial Cryptography, LNCS, vol. 12675, 3–36. Zamyatin, Alexei, Mustafa Al-Bassam, Dionysis Zindros, Eleftherios Kokoris Kogias, Pedro Moreno-Sanchez, Aggelos Kiayias, and William J. Knottenbelt. “SoK: Communication across Distributed Ledgers.” In <i>25th International Conference on Financial Cryptography and Data Security</i>, 12675:3–36. Springer Nature, 2021. <a href="https://doi.org/10.1007/978-3-662-64331-0_1">https://doi.org/10.1007/978-3-662-64331-0_1</a>. Zamyatin, Alexei, et al. “SoK: Communication across Distributed Ledgers.” <i>25th International Conference on Financial Cryptography and Data Security</i>, vol. 12675, Springer Nature, 2021, pp. 3–36, doi:<a href="https://doi.org/10.1007/978-3-662-64331-0_1">10.1007/978-3-662-64331-0_1</a>. Zamyatin A, Al-Bassam M, Zindros D, et al. SoK: Communication across distributed ledgers. In: <i>25th International Conference on Financial Cryptography and Data Security</i>. Vol 12675. Springer Nature; 2021:3-36. doi:<a href="https://doi.org/10.1007/978-3-662-64331-0_1">10.1007/978-3-662-64331-0_1</a> 103252021-11-21T23:01:29Z2023-08-14T12:59:26Z