Comment on "Arbitrated quantum-signature scheme"

TL;DR

This paper critically examines a quantum signature scheme, highlighting ambiguities in its protocol and disputing its claimed security, thereby questioning its operational clarity and robustness.

Contribution

It provides a detailed critique of the existing quantum signature scheme, identifying ambiguities and challenging its security claims.

Findings

The protocol is not clearly operationally defined.

Several steps in the scheme are ambiguous.

The claimed security is argued to be incorrect.

Abstract

We investigate the quantum signature scheme proposed by Zeng and Keitel [Phys. Rev. A 65, 042312 (2002)]. It uses Greenberger-Horne-Zeilinger (GHZ) states and the availability of a trusted arbitrator. However, in our opinion the protocol is not clearly operationally defined and several steps are ambiguous. Moreover, we argue that the security statements claimed by the authors are incorrect.