Continuous-variable quantum key distribution with a leakage from state preparation

TL;DR

This paper investigates the effects of side-channel leakage from the state preparation in continuous-variable quantum key distribution, highlighting the vulnerabilities of squeezed states and the importance of squeezing optimization for secure communication.

Contribution

It provides a detailed analysis of side-channel leakage impacts on both coherent- and squeezed-state protocols and proposes optimization strategies to mitigate these vulnerabilities.

Findings

Coherent-state protocol is immune to pre-modulation leakage.

Squeezed-state protocol is vulnerable to side-channel leakage and noise.

Squeezing optimization enhances protocol performance under leakage.

Abstract

We address side-channel leakage in a trusted preparation station of continuous-variable quantum key distribution with coherent and squeezed states. We consider two different scenaria: multimode Gaussian modulation, directly accessible to an eavesdropper, or side-channel loss of the signal states prior to the modulation stage. We show the negative impact of excessive modulation on both the coherent- and squeezed-state protocols. The impact is more pronounced for squeezed-state protocols and may require optimization of squeezing in the case of noisy quantum channels. Further, we demonstrate that coherent-state protocol is immune to side-channel signal state leakage prior to modulation, while the squeezed-state protocol is vulnerable to such attacks, becoming more sensitive to the noise in the channel. In the general case of noisy quantum channels the signal squeezing can be optimized to provide best performance of the protocol in the presence of side-channel leakage prior to modulation. Our results demonstrate that leakage from the trusted source in continuous-variable quantum key distribution should not be underestimated and squeezing optimization is needed to overcome coherent state protocols.