An In-depth Guide to Cross-chain Protocols under a Multi-chain World

In 2021, public blockchains have made remarkable progress with the support of investors and developers, ushering in the era of the multi-chain world, which represents a paradigm shift that is unlikely to be reversed. Cross-chain protocols have become an essential infrastructure in this new world, referring to a standardized set of rules and processes that enable the secure transfer of assets or information between different blockchain networks. To help researchers and industry practitioners better understand the concepts, advantages, and limitations of cross-chain technologies, this paper presents a comprehensive guide to cross-chain protocols. We cover a range of topics, including message transmission protocols, leading cross-chain bridges, and other cross-chain applications. Additionally, we discuss potential risks and challenges associated with cross-chain protocols and explore the future of cross-chain protocol development. Our work is intended to offer valuable insights and references for anyone looking to delve deeper into cross-chain protocols, whether they are academic researchers or industry professionals.