By comparing Cabello's addendum to his quantum key distribution protocol [Phys. Rev. A 64 (2001) 024301], we propose a more convenient modified protocol based on the entanglement swapping which is secure against the eavesdropping strategy addressed by Zhang et al. [Phys. Rev. A 63 (2001) 036301] and other existing types of attack.
Extending the eavesdropping strategy devised by Zhang, Li, and Guo [Zhang, Li, and Guo, Phys. Rev. A 63, 036301 (2001)], we show that the multiparty quantum communication protocol based on entanglement swapping, which was proposed by Cabello (e-print quant-ph∕0009025), is not secure. We modify the protocol so that entanglement swapping can secure multiparty quantum communication, such as multiparty quantum key distribution and quantum secret sharing of classical information, and show that the modified protocol is secure against the Zhang-Li-Guo strategy for eavesdropping as well as the basic intercept-resend attack.
Li et al. presented a protocol [International Journal of Quantum Information4(6) (2006) 899–906] for quantum key distribution based on entanglement swapping. In this protocol, they use random and certain bits to construct a classical key, and they claim that this key is secure. In our article, we show that the protocol by Li et al. is insecure, presenting a new type of attack strategy which gives an adversary full information about the key without being detected. This strategy is based on entanglement swapping, too, and manages to preserve the correlation between the measurement results of the legitimate parties. Further, we present a modified version of the protocol and show that it is secure against this new attack strategy.