Research On The Practical Security Of The Decoy State Quantum Key Distribution

Quantum key distribution has developed well both theoretically and experimentally. It has proven that QKD is unconditional security under ideal conditions. Compared with the theoretical security, practical security needs to consider the influence of the imperfections of the devices used for QKD system. Most of real-life QKD systems are based on decoy-state QKD protocol. The initial decoy-state protocol is active decoy-state protocol. And its "active" operates will introduce some side-channel information that threatens the security of QKD system.To solve this problem, passive decoy state protocol was proposed. It has higher security and less implementation complexity. Therefore, it has great significance to analyse the practical security of passive decoy-state protocol. In this paper, these three imperfections:intensity fluctuations, finite-length key and modulator attenuation are concerned. The main research works are as follows:1.Passive decoy-state QKD using weak coherent pulses (WCP) with intensity fluctuations. In this paper, we describe the WCP source that can be used for the passive decoy-state method. According to intensity fluctuation parameter δ,we characterize the fluctuation ranges of distribution probabilities. The expressions for single-photon error rates and counts are presented. And we get the key generation rate of the passive decoy-state protocol using the WCP source with intensity fluctuations.From numerical simulations, it can be seen that under the same deviation of intensity fluctuations, the passive decoy-state method performs better than the active one decoy-state method and is close to the active "vacuum+weak" decoy-state method. But the passive decoy-state method is more stable than the active "vacuum+weak" decoy-state method.2. Passive decoy-state QKD using WCP source with finite-length key. Based on the WCP source that can be used for the passive decoy-state method, we get the expressions for single-photon error rates, single-photon counts and phase error rates. Then, according to the information of smooth min-entropy, we calculate the key generation rate under the condition of finite-length key. We compare the key generation rate with different numbers of pulses by numerical simulations.From the results, it can be seen that the passive decoy-state method will be implemented well if the total number of pulses gets 1010.And we also simulate the passive decoy-state method with different probabilities of choosing a pulse for parameter estimation when the number of pulses is fixed. It can help us select the optimal value to make sure that the passive decoy-state method in this paper will be implemented best.3.Passive decoy-state QKD using WCP source with modulator attenuation. Based on the phase-coding QKD system, we use two safety equivalent models to analyse the modulator attenuation of Unbalanced Mach-Zehnder Interferometer (UMZI).One model is a perfect PM and an attenuator simulating the practical phase modulator (PM). The other one is virtual source and virtual unitary transformation simulating UMZI. Based on the WCP source used in this paper, we introduce a attenuator parameter φ.And we make a function relationship between the pass efficiencies andφ.After all, we obtain the pass efficiencies of the sender and the receiver and get the security key rates of the above two models by GLLP formula. According to the results of simulations, the key generation rate and extreme transmission distance of the virtual source and virtual unitary transformation is better than the other model.Also we can find that under the same modulator attenuation, the passive decoy-state method performs better than the active one decoy-state method and is close to the active "vacuum+weak" decoy-state method.