Reference Pulse Attack on Continuous-Variable Quantum Key Distribution with Local Local Oscillator

We reveal a security loophole in the current state-of-art phase reference pulse sharing scheme for Continuous Variable Quantum Key Distribution using a Local Local Oscillator (LLO-CVQKD). The loophole is associated with the amplitude of the phase reference pulses which Eve can manipulate to extract information which cannot be discovered by legitimate users. We call this new attack as the reference pulse attack. We have demonstrated the efficiency of our attack for different LLO-CVQKD transmission distances. Unity attack efficiency can be achieved at a transmission distance greater than 21.2 km in the case of a zero loss channel. The distance extends to 24.3 km where hollow-core fibre channels are used. We also propose possible countermeasures.