The scope of digital payment in this working paper is divided into two categories: centralized solutions and decentralized solutions. Centralized solutions are further divided into third-party payment and central bank digital currency (CBDC), while decentralized solutions are subdivided into cryptocurrency and digital identity. The development of digital payment systems can be divided into three phases – (1) transformation of traditional payment systems; (2) independent payment systems; and (3) core infrastructure. Phase 1 is the digital payment system we are using now.