Cryptographic Primitives in Script-based and Scriptless Payment Channel Networks: A Survey

Payment Channel Networks (PCNs), pivotal for blockchain scalability, facilitate multiple off-chain payments between any two users. They utilize scripts to define and execute payment conditions in various blockchains, but this poses privacy, efficiency, and compatibility challenges. To overcome these, scriptless cleverly embeds payment conditions into digital signatures instead of complex scripts. Cryptography effectively safeguards the construction and publication of transactions in script-based and scriptless PCNs. Although several surveys analyze PCN protocols, only a few discuss their underlying scripting languages and even none explore the cryptography involved. This survey is the first to comprehensively overview cryptography in PCNs from scripting perspectives, filling the existing knowledge void. Our analysis offers a complete picture of script-based and scriptless protocols and their coexistence. We then explore advanced cryptographic primitives in both categories, systematically studying these for the first time, and demonstrate their instantiations in atomic swaps. Finally, we research vast related surveys and provide a future-oriented outlook.