Sebastien Kunz-Jacques

Establishing an information-theoretic secret key between the two communicating parties of a quantum key distribution (QKD) system is only possible when an accurate characterization of the quantum channel and proper device calibration routines are combined. Indeed, security loopholes caused by inappropriate calibration routines have been shown for discrete-variable QKD. Here, we propose and provide experimental evidence of an attack targeting the local oscillator calibration routine of a continuous-variable QKD system. The attack targets the classical local oscillator pulses during the QKD run in order to modify the trigger pulses used at the detection stage. This allows the eavesdropper to bias the shot noise estimation usually performed using a calibrated relationship. This loophole can be used to perform an undetected intercept-resend attack. We characterize the loophole and suggest possible countermeasures.