Research On Security Of Quantum Key Distribution

Quantum key distribution (QKD) is essentially a technology of secret sharing based on quantum mechanics in an insecure public channel between two legitimate communicating parties Alice and Bob. The security of ideal QKD lays the foundation for investigating the security of practical QKD. Based on the widely existing information-disturbance tradeoff in quantum measurement, to analyze the security of ideal QKD has important theoretical values. In fact, unlike ideal QKD, there certainly exist some imperfections in practical QKD, such as intensity fluctuations in photon source, unavoidable errors in preparation and modulation of quantum states, inherent drawbacks of transmission device, and imperfect detecting efficiencies, which bring huge potential threat to the security of practical QKD. How much do these imperfections influence the security of practical QKD system is an issue of common concern. In this paper, mainly concentrating on information-disturbance tradeoff, intensity fluctuations and state dependent imperfections, we have a deep research on the security of QKD. The main results and creations are listed as follows.1. Research on information-disturbance tradeoff of BBM92 protocol against individual attack. The information-disturbance tradeoff of QKD protocol under specific attack strategy can provide an estimation of the amount of information that an eavesdropper can acquire, which will offer essential consults about the security analysis of QKD. However, the research on the information-disturbance tradeoff of entanglement-based QKD protocol under specific attack strategies has not yet aroused enough attention. This paper addresses an individual attack strategy against BBM92 protocol. The optimal tradeoff between the guessing capability and disturbance quantity is explicitly deducted and the optimal measurement that saturates the tradeoff bound is also presented.2. Research on decoy-state quantum key distribution for the heralded pair coherent state (HPCS) photon source with intensity fluctuations. Undoubtedly, there exists inherent intensity fluctuation in practical photon source and the HPCS photon source is not an exception. How intensity fluctuation concretely influences the final key generating rates and maximal secure communicating distance when using HPCS photon source still needs further study. This paper characterizes two important properties of the photon number distribution of the HPCS photon source. Based on the three-intensity decoy state method, the formula of secret key generation rates for the decoy-state quantum key distribution with intensity fluctuation source is proved to hold true for the HPCS photon source. By numerical simulations, we show that the three-intensity decoy-state protocols for the HPCS photon source is efficiently getting close to the ideal decoy-state method. Moreover, we find that the HPCS source is more robust against intensity fluctuation than the weak coherent photon (WCP) source, but less stable than the heralded single photon source (HSPS).3. Research on decoy state quantum key distribution based on state-dependent imperfections. In practical QKD system, the device used for state preparation and detection has immanent imperfections, which brings the problem of state-dependent imperfections. However, when it comes to the widely used decoy state method in QKD system, how state-dependent imperfections influence the security of decoy state QKD remains a question. This paper proposes models for analyzing the security of decoy state QKD with state-dependent imperfections, obtains the formula of secret key generation rates for decoy-state QKD with state-dependent imperfections, and characterizes the relationship among key generation rates, state dependent parameter, detection efficiency and transmission distance. Numerical simulations, to some extent, verify the validity of the formula we obtain.