Quantum Key Distribution with Continuous Variables in Optics

Philippe Grangier, Simon Fossier, Jérôme Lodewyck +4 more

Mao Yun, Ying Guo

Continuous variable quantum key distribution is a information system that uses quantum physics to share secret keys among legitimate participants, where a variable optical attenuator (VOA) plays a crucial role in managing the intensity of light transmitted between the participants. However, minor changes in light intensity can have an impact on its security. In this paper, we suggest an attack strategy called the laser damage attack targeting the VOA of the continuous variable (CV) measurement-device-independent (MDI) quantum key distribution (QKD) system. This attack can damage the VOA, leading to incorrect secret key rate calculations by legitimate participants and enabling an eavesdropper to steal partial secret key information. Numerical simulations show its potential impact on the practical security of the CV-MDI-QKD system.

Chenyang Li, Thomas van Himbeeck, Li Qian +1 more

Despite tremendous theoretical and experimental progress in continuous variable (CV) quantum key distribution (QKD), its security has not been rigorously established for practical systems with multiple imperfections. The idea of tagging is widely used in security proofs of discrete variable quantum key distribution with imperfect devices. In this paper, we generalize the tagging idea from discrete variable to continuous variable. Based on untagged signals, we prove the security of the imperfect quantum key distribution system in the most conservative case. By introducing a generic imperfection model, we can evaluate and further incorporate multiple imperfections in the different stages such as modulation, channel and detection. Finally, with this generic model and tagging idea, we can prove the security of continuous variable key distribution system with multiple imperfections. Our case study shows our proofs are able to provide secure keys in the presence of both modulation and detection flaws.

Eleni Diamanti

Romain Alléaume

Chenyang Li, Li Qian, Hoi‐Kwong Lo

Abstract Despite tremendous theoretical and experimental progress in continuous variable (CV) quantum key distribution (QKD), the security has not been rigorously established for most current continuous variable quantum key distribution systems that have imperfections. Among these imperfections, intensity fluctuation is one of the principal problems affecting security. In this paper, we provide simple security proofs for continuous variable quantum key distribution systems with intensity fluctuating sources. Specifically, depending on device assumptions in the source, the imperfect systems are divided into two general cases for security proofs. In the most conservative case, we prove the security based on the tagging idea, which is a main technique for the security proof of discrete variable quantum key distribution. Our proofs are simple to implement without any hardware adjustment for current continuous variable quantum key distribution systems. Also, we show that our proofs are able to provide secure secret keys in the finite-size scenario.