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We present an improvement of the protocol proposed by Lucamarini and Mancini [M. Lucamarini, S. Mancini, Phys. Rev. Lett. 94 (2005) 140501] with techniques used in the protocol presented by Zhu et al. [A.D. Zhu, Y. Xia, Q.B. Fan, S. Zhang, Phys. Rev. A 73 (2006) 022338], namely the secret transmitting order of particles.
In this comment, we show that the security of the schemes proposed by Lee et al. [H. Lee, C. Hong, H. Kim, J. Lim, H.J. Yang, Phys. Lett. A 321 (2004) 295–300] does not rely on the usage of entanglement and the GHZ triplet states used in their schemes can be replaced by classical correlated states.
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