Flexible quantum tokens in spacetime
This work addresses secure quantum token systems for networks with trusted signalling constraints, presenting an incremental refinement of existing S-money schemes.
The authors tackled the problem of creating secure quantum tokens for networks with relativistic constraints by refining S-money schemes into two stages, allowing users to determine token presentation points anywhere in the causal past of valid points and enabling flexible token transfers without compromising privacy.
S-money [Proc. R. Soc. A 475, 20190170 (2019)] schemes define virtual tokens designed for networks with relativistic or other trusted signalling constraints. The tokens allow near-instant verification and guarantee unforgeability without requiring quantum state storage. We present refined two stage S-money schemes. The first stage, which may involve quantum information exchange, generates private user token data. In the second stage, which need only involve classical communications, users determine the valid presentation point, without revealing it to the issuer. This refinement allows the user to determine the presentation point anywhere in the causal past of all valid presentation points. It also allows flexible transfer of tokens among users without compromising user privacy.