The Research Of Vulnerability Mining Methods Of SPDs In High-speed QKD Systems

Quantum key distribution(QKD)is the core of quantum secure communication,which can provide the unconditionally secure private communication between two users in principle.The security of QKD is based on fundamental principles of quantum mechanics.However,in the practical applications,there is always a gap between the practical devices and the theoretical models.These imperfections bring various security risks to the QKD systems.At present,the main constraint of the security key rate in QKD is still the single photon detector(SPD).Therefore,the application of single photon detector is significant for QKD systems,and the research on the vulnerability mining of SPDs is crucial for the practical security of high-speed QKD systems.This paper focuses on the practical security and studies the vulnerability mining of two kinds of SPDs — the sine-wave gating single-photon detector(SG-SPD)and the superconducting nanowire single photon detector(SNSPD)in high-speed QKD systems.The main work of this paper is summarized as follows:1.The analysis of vulnerability mining principle of the sine-wave gating single photon detector.The SG-SPD is one kind of GHz SPDs used in the high-speed QKD systems,and the analysis of its practical security and the vulnerability mining methods is not sufficient.This paper analyzes the SG-SPD's working principle and parameter characteristics to find the potential loopholes,then we establish the mathematical models of the avalanche signal,the gating noise suppression and other core parameters of the SG-SPD,what's more,we simulate the SG-SPD's detection process with Matlab.The simulation results indicate that the SG-SPD has the filtering loophole which can be exploited by an Eve to blind the SG-SPD with the bright light.2.The vulnerability mining experiment of the filtering loophole of the SG-SPD.Basing on the vulnerability mining principle of the SG-SPD,we design an experiment scheme and set up the experiment platform with three modules: the SG-SPD,the clock and synchronization system,and the picosecond pulse laser.In the experiment,we find that the SG-SPD could be blinded by the bright laser pulse.Further,we could control the SG-SPD by adding the controlling laser pulse with frequency different from the sine-waving gating signal.Under the controlling laser pulse,the count rate of the SG-SPD shows the characteristic of super-linearity.Finally,we analyze the influence of the filtering loophole in the practical QKD systems and discuss the countermeasures aimed at this loophole..3.The analysis of vulnerability mining principle of the SNSPD.The SNSPD receives extensive attention these years with high detection efficiency,low dark count rate,and low time jitter.This paper analyzes the working principle and the parameter characteristics of SNSPD,studying the electric model,the thermal model and the dynamic inductance's model of the SNSPD.Basing on these mathematical models,we analyze the relationship between the circuit resistance with temperature and the bias current.Further,we analyze change of these parameters in the dead time of the SNSPD,finding that the SNSPD could respond the bright laser pulse in its dead time.Finally,we give the scheme of vulnerability mining in experiment aimed at the dead time loophole of the SNSPD.4.The vulnerability mining experiment of the dead time loophole of the SNSPD.Basing on the theoretical analysis that the SNSPD could still generate a response under the bright laser pulse,we design an experiment platform to verify the hypothesis.By testing the response of the SNSPD in its dead time,we find that with the weak trigger pulse of 72 photons/pulse,the response of SNSPD under the controlling laser pulse behaves the super-linear characteristic.This super-linear characteristic could be exploited by Eve to obtain the secret key.Finally,we perform an experimental demonstration about the intercept and resend attack in the practical phase-coded QKD system.Further,we discuss the process of Eve stealing the secret keys in the intercept and resend attack.