Polarization attack on continuous-variable quantum key distribution

Abstract

The shot-noise unit (SNU) is a crucial factor for the practical security of a continuous-variable quantum key distribution system. In the most widely used experimental scheme, the SNU should be calibrated first and acts as a constant during the key distribution. However, the SNU of a practical system is dependent on the various parameters of the local oscillator, which can be controlled by the eavesdropper in the open channel. In this paper, we report a quantum hacking method to control the practical SNU by using the limited compensation rate of the polarization compensation. Since the compensation is only based on of the polarization measurement results of part of local oscillator pulses, the polarization of other unmeasured pulses may not be compensated correctly, which can be utilized by the eavesdropper to control the practical SNU. The simulation and experiment results indicate that the practical SNU can be controlled by the eavesdropper. Thus, the eavesdropper can use the fact that the practical SNU is no longer equals to the calibrated one to control the excess noise and final key rate.

Advances in quantum cryptography

“…However, they found that by adding a third attenuation value (rather than just on or off) to the strong attenuation could prevent their attack. Xie et al [553] also found that a jitter effect in the clock signal can lead to an incorrect calculation of the shot noise, and Zhao et al [554] identified a polarization attack where the eavesdropper attacks unmeasured LO pulses to control and tamper with the shot-noise unit of the protocol.…”

Fading channel estimation for free-space continuous-variable secure quantum communication

“…It is furthermore worth noting that even though the local estimator plays an important role during homodyne measurements, we did not include it in our analysis as this is rather a technical issue and can even be avoided. Similarly to our signal, the local oscillator is also subject to fluctuations and it also has to be estimated [41], but its estimation is considerably easier due to its high power and the fact that we only need to know its intensity. So the normalization of the local oscillator can be performed with high precision.…”

Polarization diverse true heterodyne receiver for continuous variable quantum key distribution

“…When implemented over standard optical fibres, one such noise source is random polarization drift in the communication channel, which will degrade the efficiency of the coherent detection scheme [3]. Therefore a polarization drift compensation scheme is strictly necessary for the implementation of efficient and secure CV-QKD systems [2,[4][5][6].…”