Flexible quantum tokens in spacetime

TL;DR

This paper introduces refined S-money schemes enabling flexible, privacy-preserving token presentation in spacetime, combining quantum and classical communication for near-instant verification and transfer.

Contribution

It presents a two-stage S-money scheme allowing user-controlled presentation points and flexible token transfer without compromising privacy.

Findings

Supports presentation anywhere in the causal past of valid points

Enables transfer of tokens among users without privacy loss

Maintains unforgeability and instant verification

Abstract

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.