AT-CBDC: Achieving Anonymity and Traceability in Central Bank Digital Currency

In this paper, we propose a new central bank digital currency (CBDC) system based on the two-tier architecture. The proposed system enhances the traditional bank-user framework of electronic cash and employs the commercial banks for account and coin management. The coin splitting is supported during coin withdrawal of users and the coin combination is achieved for coin deposit at the commercial banks, such that the efficiency of coin management is improved. The other distinguished feature is that the proposed system achieves the anonymity against the commercial banks, while enabling the central bank to support user tracing and double-spending prevention. Specifically, by utilizing the BBS+ signatures, the users can create bank accounts, withdraw coins, and deposit the received coins at the commercial banks without exposing their real identities. As a trusted party, the central bank is responsible for money issuing and financial regulation. In addition, to ensure the system inclusive, users can receive payments from others even they do not have bank accounts at commercial banks. Finally, we demonstrate that the proposed system achieves the desirable properties of balance, anonymity, and traceability and show the efficiency and practicality for the implementation on mobile devices.