Improvements on “Multi-party Quantum Key Agreement Protocol with Bell States and Single Particles”

Liu et al. (Int. J. Theor. Phys. 58 (5), 1659–1666 2019 ) proposed a multi-party quantum key agreement protocol with Bell states and single particles. They claimed that their protocol can resist the participant and outside attacks. However, we found that their protocol does not provide the fairness property and cannot resist collusion attacks. The last involved participant in Part P can conspire with anyone of the participants in Part Q to manipulate the final shared key without being detected. Moreover, two improved protocols depending on different strategies are proposed, in which the security and the fairness are both enhanced.