Central Bank Digital Currencies (CBDCs) are proposed as a public response to the uptake of privately run digital payments, with the digital euro, under development by the European Central Bank (ECB), serving as a prominent example. 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 start. While the central banks in charge are investigating privacy-enhancing technologies (PETs), they often conclude that PETs are immature or insufficiently scalable. Moreover, these efforts tend to examine primitives in isolation, offering little insight into how a system using these PETs would scale. This systematisation of knowledge, therefore, provides a structured, top-down technical analysis of 36 payment system designs of complete system proposals that can inform CBDC designs or were explicitly proposed for this application. We identify recurring design patterns, technical trade-offs, and implementation challenges. Concluding, we highlight research gaps, including offline payments and post-quantum security.

翻译：央行数字货币（CBDC）被提出作为对私营数字支付兴起的公共回应，其中由欧洲中央银行（ECB）正在开发的数字欧元即是一个突出范例。这一趋势为从根本上重新思考货币的未来提供了独特机遇，并且假设其被广泛采用，可以建立从一开始就提供强大密码学安全性和隐私保障的支付系统。尽管负责的中央银行正在研究隐私增强技术（PET），但它们常得出PET不成熟或可扩展性不足的结论。此外，这些努力往往孤立地考察密码学原语，对于使用这些PET的系统将如何扩展提供的信息有限。因此，本知识体系化工作对36个完整系统提案的支付系统设计进行了结构化、自上而下的技术分析，这些设计可为CBDC设计提供参考或明确为此应用提出。我们识别了重复出现的设计模式、技术权衡和实施挑战。最后，我们指出了包括离线支付和后量子安全在内的研究空白。