Experimental demonstration of a coherent detector blinding attack on a real CV-QKD system

Abstract: Continuous-variable quantum key distribution provides a theoretical unconditionally secure solution to distribute symmetric keys among users in a communication network. However, the practical devices used to implement these systems are intrinsically imperfect, and, as a result, open the door to eavesdropper attacks. In this work, we present a novel implementation of a coherent detector blinding attack, in which the eavesdropper hinders the capability of the receiver to properly estimate the channel parameters, hiding the impact of their collective attack. Our results show that excess noise in excess of 2.5 SNU can be reliably hidden by the eavesdropper, thus demonstrating the feasibility of the attack. We also discuss how our attack strategy can be further improved to allow for even stronger attacks (by using more advanced modulation formats), and propose some countermeasures to prevent it.