xPayments: Cross-Domain End-to-End Payment Protocol using Payment Channel Network

The rapid integration of digital technologies has precipitated a substantial transition from traditional in-person commerce to digital trade, even encompassing physical goods. This transformation not only simplifies the purchasing process but also broadens the market reach for vendors, enabling global connectivity with consumers. Presently, there is a shift towards Metaverse-based applications, with blockchains serving as the foundational infrastructure for data management, thereby enhancing the overall user experience. Given this context, integrating payment methods becomes pivotal, particularly in light of the widespread adoption of blockchain technology. Our proposal introduces xPayment, a decentralised payment protocol designed to facilitate end-to-end and cross-domain transactions for digital goods via payment channel networks (PCNs). Initially, we introduce the concept of cyclic exchange and formally demonstrate its atomicity, on which we develop xPayment protocol to facilitate an independent and interoperable payment mechanism integrated into blockchain-based ownership transfers. We provide both theoretical and empirical evidence of its atomicity, minimal merchant opportunity cost, and customisable privacy features.