Quantum control attack: towards joint estimation of protocol and hardware loopholes

In this paper we present the approach for description of quantum control attack based on combined protocol and hardware loopholes. It consolidates intercept-resend attack and detection node control (detector blinding attack). In the basic version of B92 protocol detection control is not that crucial; however, when one scales the number of states the state imposing plays a significant role. Protocols that operate with arbitrary even symmetric linearly independent nonorthogonal (e.g., coherent) states are of interest. The cornerstone of the considered approach is that we combine both state discrimination by eavesdropper and different methods of state imposing. In principle, detection control allows one to exclude any bit correlations between legitimate users, which are unknown to Eve, and can be considered as the necessary part of most intercept-resend attacks, including a faked- state attack impossible without a hardware loophole. Moreover, the issue related to unified quantum description of the intercept-resend attack was solved by combining the concepts of von Neumann’s measurement scheme and ambiguity of square root extraction for operators. We also present a generalized countermeasure based on additional parameter estimation analysis. As an example, with some numerical estimations we investigate the attack on quantum key distribution systems based on utilization of