Breaking and making quantum money: toward a new quantum cryptographic protocol

TL;DR

This paper explores the security challenges of public-key quantum money, introduces the concept of collision-free protocols, and provides a blueprint and example, highlighting potential vulnerabilities in current schemes.

Contribution

It proposes the first framework for collision-free quantum money protocols and offers a concrete example, advancing understanding of quantum money security.

Findings

Existing public-key quantum money schemes are insecure.

Collision-free protocols prevent the bank from producing identical quantum bills.

The provided example may be insecure, indicating the need for further research.

Abstract

Public-key quantum money is a cryptographic protocol in which a bank can create quantum states which anyone can verify but no one except possibly the bank can clone or forge. There are no secure public-key quantum money schemes in the literature; as we show in this paper, the only previously published scheme [1] is insecure. We introduce a category of quantum money protocols which we call collision-free. For these protocols, even the bank cannot prepare multiple identical-looking pieces of quantum money. We present a blueprint for how such a protocol might work as well as a concrete example which we believe may be insecure.