Two attacks and counterattacks on the mutual semi-quantum key agreement protocol using Bell states

TL;DR

This paper analyzes a semi-quantum key agreement protocol using Bell states, revealing vulnerabilities where the classical participant can manipulate the key, and proposes an improved method to prevent this manipulation.

Contribution

The paper identifies security flaws in Yan et al.'s protocol and introduces an improved method to ensure fair key sharing between quantum and classical participants.

Findings

Classical participant can manipulate the shared key undetected

Two attacks demonstrate vulnerabilities in the original protocol

An improved protocol counteracts the identified attacks

Abstract

Recently, a mutual semi-quantum key agreement protocol using Bell states is proposed by Yan et al. (Mod. Phys. Lett. A, 34, 1950294, 2019). The proposed protocol tries to help a quantum participant share a key with a classical participant who just has limited quantum capacities. Yan et al. claimed that both the participants have the same influence on the final shared key. However, this study points out that the classical participant can manipulate the final shared key by himself/herself without being detected. To solve this problem, an improved method is proposed here.