Modulation leakage vulnerability in continuous-variable quantum key distribution

TL;DR

This paper identifies a modulation leakage vulnerability in continuous-variable quantum key distribution systems caused by imperfect suppression of sidebands, which can compromise security and reduce effective communication range.

Contribution

It reports a specific modulation leakage flaw in a CV-QKD system, analyzes its impact, and evaluates countermeasures like trusted noise.

Findings

Leakage reduces secure communication distance

Leakage can cause security breaches if unaddressed

Trusted noise can mitigate leakage effects

Abstract

Flaws in the process of modulation, or encoding of key bits in the quadratures of the electromagnetic light field, can make continuous-variable quantum key distribution systems susceptible to leakage of secret information. Here, we report such a modulation leakage vulnerability in a system that uses an optical in-phase and quadrature modulator to implement a single sideband encoding scheme. The leakage arises from the limited suppression of a quantum-information-carrying sideband during modulation. Based on the results from a proof-of-concept experiment, we theoretically analyse the impact of this vulnerability. Our results indicate that the leakage reduces the range over which a positive secret key can be obtained, and can even lead to a security breach if not properly taken into account. We also study the effectiveness of additional trusted noise as a countermeasure to this vulnerability.