The Security Analysis Of The Two-step Quantum Direct Communication Protocol In Collective-rotation Noise Channel

With the development of computer science and technology, people pay more and more attention to the security of information. The traditional security detection schemes have been unable to meet the requirements of information security. A new and more efficient method of security detection is becoming the object pursed by many scholar.Fortunately, with the development of quantum communication technology,a variety of quantum communication schemes have been proposed. As a new quantum secure communication technology, Quantum secure direct communication technology has much more advantages than the tranditional security detection schemes, and the research on direct communication technology is of great theoretical significance. In 2003,FuGuo Deng et al. proposed a two-step quantum secure direct communication protocol which based on EPR pairs, and discussed the basic principle and safety analysis of the protocol. But the discussion on the security of this protocol is rarely related to the noise, but the noise of the environment is inevitable. So, the safety analysis of the two-step quantum secure direct communication protocol in the noise environment becomes very meaningful, which can provide a theoretical basis for studying new quantum secure direct communication protocol in the future and accelerate the realization of quantum secure direct communication utility.To analysis the security of two-step quantum direct communication protocol (QDCP) using Einstein-Podolsky-Rosed (EPR) pair proposed by Fu-Guo Deng and Gui-Lu Long[1], etc. 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 Q0(M: (Q0,1.0) is given. In different noise level, if Eve wants to get the same amount of information, the error rate Q is distinguishing: The larger the noise level ? is, the larger the error rate Q is. When the noise level ? is lower than 11%, the high error rate is 0.153 without eavesdropping. At last, 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 = Q0, eavesdropping information I>1, which means there exists eavesdroppers in the quantum channel, and the quantum channel will not be safe any more.