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.
We provide a security analysis of continuous-variable quantum key distribution (CVQKD) with discrete modulation against general attacks in a realistic finite-size regime. To realize this goal, we first prove security of the continuous-variable quantum key distribution protocol with discrete modulation against collective attacks by using the reliable tomography of the covariance matrix, leading to the reliable and tight error bounds in the derived confidence regions. Combining the proof with de Finetti reduction, the discrete-modulation-based continuous-variable quantum key distribution (DM-CVQKD) is proved to be secure even exposing to general attacks. Specially, we use an energy test to truncate the Hilbert space globally to provide security.