Central Bank Digital Currency (CBDCs) are becoming a new digital financial tool aimed at financial inclusion, increased monetary stability, and improved efficiency of payment systems, as they are issued by central banks. One of the most important aspects is that the CBDC must offer secure offline payment methods to users, allowing them to retain cash-like access without violating Anti-Money Laundering and Counter-terrorism Financing (AML/CFT) rules. The offline CBDC ecosystems will provide financial inclusion, empower underserved communities, and ensure equitable access to digital payments, even in connectivity-poor remote locations. With the rapid growth of Internet of Things (IoT) devices in our everyday lives, they are capable of performing secure digital transactions. Integrating offline CBDC payment with IoT devices enables seamless, automated payment without internet connectivity. However, IoT devices face special challenges due to their resource-constrained nature. This makes it difficult to include features such as double-spending prevention, privacy preservation, low-computation operation, and digital identity management. The work proposes a privacy-preserving offline CBDC model with integrated secure elements (SEs), zero-knowledge proofs (ZKPs), and intermittent synchronisation to conduct offline payments on IoT hardware. The proposed model is based on recent improvements in offline CBDC prototypes, regulations and cryptographic design choices such as hybrid architecture that involves using combination of online and offline payment in IoT devices using secure hardware with lightweight zero-knowledge proof cryptographic algorithm.

翻译：央行数字货币正成为一种新型数字金融工具，由中央银行发行，旨在促进金融包容性、增强货币稳定性并提升支付系统效率。其中最关键的一点在于，央行数字货币必须为用户提供安全的离线支付方式，使其在保持类现金可及性的同时不违反反洗钱和反恐怖主义融资规则。离线央行数字货币生态系统将推动金融包容，赋能服务不足的社区，并确保即使在网络覆盖薄弱的偏远地区也能实现数字支付的公平接入。随着物联网设备在日常生活中的快速增长，它们已具备执行安全数字交易的能力。将离线央行数字货币支付与物联网设备相结合，可实现无需网络连接的自动化无缝支付。然而，物联网设备因其资源受限的特性面临特殊挑战，这使得集成防双花、隐私保护、低计算量操作和数字身份管理等功能变得困难。本研究提出一种融合安全元件、零知识证明与间歇同步机制的隐私保护型离线央行数字货币模型，可在物联网硬件上执行离线支付。该模型基于离线央行数字货币原型的最新进展、监管框架及密码学设计方案，采用混合架构——通过搭载轻量级零知识证明密码算法的安全硬件，在物联网设备中实现在线与离线支付的协同运作。