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To analyze the security of two-step quantum direct communication protocol(QDCP) by using Einstein-PodolskyRosen pair proposed by Deng et al.[Phys.Rev.A 68(2003) 042317]in collective-rotation noise channel,an excellent model of noise analysis is proposed.In the security analysis,the method of the entropy theory is introduced,and is compared with QDCP,an error rate point Q_0(M:(Q_0,1.0)) is given.In different noise levels,if Eve wants to obtain the same amount of information,the error rate Q is distinguishable.The larger the noise level ε is,the larger the error rate Q is.When the noise level e is lower than 11%,the high error rate is 0.153 without eavesdropping.Lastly,the security of the proposed protocol is discussed.It turns out that the quantum channel will be safe when Q < 0.153.Similarly,if error rate Q > 0.153 = Q_0,eavesdropping information I > 1,which means that there exist eavesdroppers in the quantum channel,and the quantum channel will not be safe anymore.
To analyze the security of two-step quantum direct communication protocol (QDCP) by using Einstein-Podolsky Rosen pair proposed by Deng et al. [Phys. Rev. A 68 (2003) 042317] in collective-rotation noise channel, an excellent model of noise analysis is proposed. In the security analysis, the method of the entropy theory is introduced, and compared with QDCP, an error rate point Q_0 (M: (Q_0, 1.0)) is given. different noise levels, if to obtain the same amount of information, the error rate Q is distinguishable. The larger the noise level ε is, the larger the error rate Q is.When the noise level e is lower than 11%, the high error rate is 0.153 without eavesdropping .Lastly, the security of the proposed protocol is discussed. It turns out that the quantum channel will be safe when Q <0.153.Similarly, if error rate Q> 0.153 = Q_0, eavesdropping information I> 1, which means that there exist eavesdroppers in the quantum channel, and the quantum channel will not be safe anymore.