Controlling passively quenched single photon detectors by bright light

Abstract

Single photon detectors (SPDs) based on passively quenched
\navalanche photodiodes can be temporarily blinded by relatively bright light, of
\nintensity less than 1nW. A bright-light regime suitable for attacking a quantum
\nkey distribution system containing such detectors is described in this paper. In
\nthis regime, all SPDs in the receiver Bob are uniformly blinded by continuous
\nillumination coming from the eavesdropper Eve. When Eve needs a certain
\ndetector in Bob to produce a click, she modifies the polarization (or other
\nparameters used to encode quantum states) of the light she sends to Bob such
\nthat the target detector stops receiving light, while the other detector(s) continue
\nto be illuminated. The target detector regains single photon sensitivity and, when
\nEve modifies the polarization again, produces a single click. Thus, Eve has
\nfull control of Bob and can perform a successful intercept–resend attack. To
\ncheck the feasibility of the attack, three different models of passively quenched
\ndetectors have been tested. In the experiment, I have simulated the intensity
\ndiagrams the detectors would receive in a real QKD system under attack. Control
\nparameters and side effects are considered. It appears that the attack could be
\npractically possible.