Research On Attacking And Defensing Scheme In Continuous-Variable Coherent Optical Communication

Continuous variable quantum key distribution(CV QKD)is a quantum communication technique that distributes a secret key between legitimate parties(Alice and Bob)through a quantum channel and a classical channel.The core value of CV QKD lies in its security.Noise and attack are the two important factors that affect the security of CV QKD.Noise of CV QKD can be divided into two kinds:trusted noise and untrusted noise.The trusted noise is caused by the imperfect performance of the devices of legitimate parties,including preparation of noise and detection noise.The detection noise is equivalent to adding some additive noise to the detection side.Although trusted noise is not available to potential eavesdroppers(Eve),it has been shown that it will affect the security of the one-way CV QKD and two-way CV QKD schemes.In this paper,we focus on the security of two new schemes,CV MDI-QKD and CV QKD with untrusted source.The contents include:1.Study on security of CV MDI-QKD with preparation noise.Considering that the preparation noise is unavoidable in the actual preparation process of coherent state,the influence of the preparation noise on the security of CV MDI-QKD scheme is considered.A model of CV MDI-QKD system with preparation noise is proposed,and the security of this noisy system is analyzed.On this basis,a scheme of using tunable attenuator to improve the performance of CV MDI-QKD system is presented.The MATLAB simulation results show that the preparation noise will seriously decrease the system’s key rate and transmission distance.By adaptively attenuating the signals sent by the coordinator(i.e.,Bob),the transmission distance of the system can be increased.2.Study on security of CV QKD with untrusted source.Considering the positive effect of additive noise on improving the performance of one-way and two-way CV QKD systems,the idea of "beating noise with noise" is introduced into the CV QKD with untrusted source,That is,Bob firstly mixes the received signal with additive noise,and then measures the noise-added signal.With appropriate additive noise,Bob can reduce the amount of information that can be handled by Eve as well as the amount of mutual information between legitimate parties.Therefore,from the whole point of view,the key rate can be optimized by adjusting the additive noise variance.The simulation results show that when the variance of the source is 40 and the extra noise is 0.1 shot-noise unit,the transmission distance of the system can be increased by 3 km,and the tolerable noise can be increased by 0.08 shot-noise units.3.Study on security of CV QKD with untrusted source under two-mode coherent attack.In the one-mode collective attack model aimed at CV QKD protocol with untrusted source,there is no correlation between the two quantum channels connecting Alice and Bob.The two-mode coherent attack model where the two quantum channels having correlation is introduced into the CV QKD protocol with untrusted source.The security of the case is analyzed.The simulation results show that when the coherent coefficient satisfies g1=-g2 =(?)N-1,the two-mode coherent attack scheme breaks the security threshold of the system under the original single-mode collective attack,which is the strongest attack scheme for the system.