Overview
The Swiss National Bank is entrusted with the note-issuing privilege in Switzerland. The banknotes need to meet high security standards. In particular, it must not be possible to copy banknotes.
The no-cloning principle for quantum states can be used for copy-protection in monetary schemes – so-called Quantum Money. The proposed and analyzed schemes date back to the beginning of quantum information as a research field in the 1970’s.
However, from a business perspective the protocols are considered impractical. One of the reasons is that they do not match the architecture of the monetary market: traditional banknotes are issued by a central bank, but distributed to consumers by retail banks. The consumers need not interact directly with the central bank. Further questions are also open: how can quantum money be “lifecycled”? How are damaged banknotes handled and under what condition can they be replaced? How can forged banknotes be recognized? How can it be ensured, that quantum cash can be used by everyone? How to deal with imperfections and losses increasing over time?
These questions are not addressed by the currently proposed quantum protocols and prevent a practical rollout of quantum money in the nearer future. In this project, the Swiss National Bank and Hochschule Luzern develop a viable quantum money scheme that fits the architectural requirements of the monetary system, complies with regulatory requirements, and can be technologically implemented. The work encompasses the proposition of a technical cryptographic protocol for quantum money; its security analysis; and a plan for its practical implementation. Remaining technical challenges are clearly identified and ways to circumvent or remove them are developed. The developed security concept serves as basis to implement a proof-of-concept of central bank quantum money in the future.
