Research On The Practical Security And Application Of Quantum Cryptography

Quantum key distribution(QKD) provides the two parties in the communication a method of sharing unconditionally secure keys. The security analysis and practical application are two major researches of QKD.Now the security of most QKD protocols under coherent attack has been proven theoreritically. However, this doesn’t necessarily represent the security of its practical implementation. For example, the actual device may work not perfectly the same as it is assumed in a theoretical analysis. This non-perfect performance of device may be utilized by the eavesdropper to secretly get part of or even all the keys. What’s more, in practical situation the length of keys is always limited, while in the theoretical analysis it is considered to be infinitely long, which means that the key rate formula needs to be corrected to incorporate the fluctuation due to the limited length. Therefore, the security of a practical QKD system requires more rigorous and more complex analysis than in the theoretical scenario. This is the hot field of QKD now.In the aspect of QKD’s application, after decades of development, QKD has been made to meet the networking requirements. The combination of QKD technology and classical network is able to take full advantage of quantum cryptography and effectively protect the user’s privacy. And the application of QKD in real-life circumstances has aroused more and more interest worldwide. It needs to consider the characteristics of the network and the user requirementsThis paper focuses on the study of practical security of the QKD system and its real-life application.The paper’s structure is as follows.We first studied the security of the BB84protocol with decoy state under partial photon number splitting(PNS) attack. The strategy of partial PNS attack is analysed in detail and an abstract model of this attack based on the photon number distribution is given. By comparing the theoretical result and lower bound of the single-photon’s gain, it is shown that the BB84protocol with decoy state is secure under partial PNS attack.As another investigation into the decoy state, we studied the influence of the random number, which is used to randomly prepare the state in decoy protocol, on the security. In this study we proposed two kinds of random number attack strategies and studied the amount of information the eavesdropper can get. Among these two strategies the second one enables the eavesdropper to know all the information about the keys with the knowledge of only a fraction p of the random number. We found that the fraction of random numbers which is needed for the eavesdropper to fully know the keys decreases exponentially with increase in distance.Then we studied the key rate at the presence of dead time in the detector. With Monte Carlo method, we conveniently simulated the process and obtained the optimal dead time for the highest key rate. The method takes into account the dark counts and after-pulses, which is very instructive for practical experiments.In the last part of security analysis, we conducted a research into the effect of the vacuum state fluctuation on the key rate for the vacuum+decoy state protocol. The results shows that, given the overall pulse number, there exists an optimal ratio of vacuum state in the pulses that leads to the highest key rate.The second major part of this paper focuses on the feasibility of applying the QKD system into the electricity grid system. Considering the specific environment in the electricity grid system(for example, the aerial fiber), we proposed the solution that is suitable for the electricity grid system, including many detailed aspects such as the encoding method and synchronizing mode.Next we analysed the security requirements of electricity system and designed two sample circumstances of applying the QKD. The first is to utilize the QKD to enhance the security of the SSL VPN data transmission. We studied the characteristics of data transmission in electricity grid system and proposed four modes for practical QKD application, and designed the protocol for the utilization and management of secret keys. The second circumstance is to improve the security of WiMAX wireless communication in electricity grid system. In this circumstance, the secret keys are stored and read out in blocks. A twofold encryption method is proposed and its related data formats are also given. The data is first encrypted with secret keys obtained from QKD and then transmitted by WiMAX.