Abstract
Central Bank Digital Currencies (CBDCs) have been suggested as a public response to the growing popularity of privately run digital payment systems. A prominent example for this is the Digital Euro, which is currently being developed by the European Central Bank (ECB). This momentum provides a unique opportunity to fundamentally rethink the future of money, and, assuming wide adoption, to establish payment systems that offer strong cryptographic security and privacy guarantees from the outset. While the central banks in charge are investigating privacy-enhancing technologies (PETs), they often conclude that PETs are premature or insufficiently scalable. Moreover, these efforts tend to examine primitives in isolation, providing limited insight into how a system using them would scale. Our structured, top-down technical analysis of 36 payment system designs in the literature identifies recurring design patterns, technical trade-offs, and implementation challenges.