Cryptanalysis of a multi-party quantum key agreement protocol with single particles

TL;DR

This paper critically analyzes a recent multi-party quantum key agreement protocol, revealing vulnerabilities where neighboring participants can eavesdrop and dishonest parties can compromise the final key, challenging its claimed security and fairness.

Contribution

The paper identifies security flaws in Sun et al.'s protocol, demonstrating potential eavesdropping and collusion attacks that compromise its fairness and security.

Findings

Neighboring participants can eavesdrop on sub-secret keys.

Dishonest participants can determine the final shared key.

The protocol's security assumptions are flawed.

Abstract

Recently, Sun et al. [Quant Inf Proc DOI: 10.1007/s11128-013-0569-x] presented an efficient multi-party quantum key agreement (QKA) protocol by employing single particles and unitary operations. The aim of this protocol is to fairly and securely negotiate a secret session key among $N$ parties with a high qubit efficiency. In addition, the authors claimed that no participant can learn anything more than his/her prescribed output in this protocol, i.e., the sub-secret keys of the participants can be kept secret during the protocol. However, here we points out that the sub-secret of a participant in Sun et al.'s protocol can be eavesdropped by the two participants next to him/her. In addition, a certain number of dishonest participants can fully determine the final shared key in this protocol. Finally, we discuss the factors that should be considered when designing a really fair and secure QKA protocol.