Reference pulse attack on continuous variable quantum key distribution with local local oscillator under trusted phase noise

We show that partially trusting the phase noise associated with estimation uncertainty in a local local oscillator continuous-variable quantum key distribution (LLO-CVQKD) system allows one to exchange higher secure key rates than in the case of untrusted phase noise. However, this opens a security loophole through the manipulation of the reference pulse amplitude. We label this as a “reference pulse attack,” which is applicable to all LLO-CVQKD systems if the phase noise is trusted. We show that, at the optimal reference pulse intensity level, Eve achieves unity attack efficiency at 23.8 km and 32.0 km while using lossless and 0.14 dB/km loss channels, respectively, for her attack. However, to maintain the performance enhancement from partially trusting the phase noise, countermeasures have been proposed. As a result, the LLO-CVQKD system with partially trusted phase noise owns a superior key rate at 20 km by an order 9.5, and an extended transmission distance by 45%, compared to the phase noise untrusted system.