Project Aurum: New Completed Hong Kong Retail CBDC Prototype with a CBDC-Backed Stablecoin

The Hong Kong Monetary Authority presented its completed Aurum retail central bank digital currency (CBDC) prototype on Oct. 21. The system, developed in conjunction with the Bank for International Settlements (BIS) Innovation Hub, has a unique structure that reflects the intricacies of the existing system for issuing money in Hong Kong.

Project Aurum is a collaboration between the BIS Innovation Hub Hong Kong Centre, the Hong Kong Monetary Authority, and the Hong Kong Applied Science and Technology Research Institute.

Aurum is a full-stack (front-end and back-end) central bank digital currency (CBDC) system comprising a wholesale interbank system and a retail e-wallet system. The aim was to bring to life two very different types of tokens: intermediated CBDC and stablecoins backed by CBDC in the interbank system. The latter is unique in the study of CBDC to date. Privacy, safety and flexibility are core to the system.

The project consists of a wholesale interbank system and retail e-wallet. The e-wallet is created at a local bank and has a smartphone interface. A validator system prevents bank over-issuance and user double redemption.

The intermediated retail CBDC is used in the e-wallets, and CBDC-backed stablecoins are used in the interbank system. The unusual CBDC-backed stablecoins digitally mirror Hong Kong’s existing currency system, in which bank notes are issued by three financial institutions and backed by the central bank. The CBDC is a direct liability of the central bank, while the stablecoins are liabilities of the issuing bank, with backing assets held by the central bank. The authors stated:

“Bringing CBDC-backed stablecoins to life has never been done before and we therefore felt that doing so may supplement the growing body of research on private sector stablecoins. Indeed, what distinguishes Aurum from private sector stablecoins is that Aurum’s stablecoin balances are reconciled, versus real time gross settlement (RTGS) balances of the issuing bank with the central bank.”
The high level of decoupling between the wholesale and retail ledgers gives the system a high level of cyber-resilience, the designer said.

Retail transactions are performed with aliases. Only the intermediary that performs Know Your Customer functions can see the identity of users. Unspent transaction output records are used to track digital currency ownership anonymously through multiple transactions as a safety measure in case of commercial bank bankruptcy.

Hong Kong launched its CBDC research in June 2021 as part of its comprehensive Fintech 2025 Strategy. The monetary authority is pursuing retail and wholesale CBDC implementation separately. It noted earlier that the retail CBDC has no “imminent role” to play in the payments market, but use cases may emerge quickly. Aurum is the first project completed by the BIS Innovation Hub.