Quantum eavesdropping without interception: an attack exploiting the dead time of single-photon detectors

Abstract

The security of quantum key distribution (QKD) can easily be obscured if the\neavesdropper can utilize technical imperfections of the actual implementation.\nHere we describe and experimentally demonstrate a very simple but highly\neffective attack which even does not need to intercept the quantum channel at\nall. Only by exploiting the dead time effect of single photon detectors the\neavesdropper is able to gain (asymptotically) full information about the\ngenerated keys without being detected by state-of-the-art QKD protocols. In our\nexperiment, the eavesdropper inferred up to 98.8% of the key correctly, without\nincreasing the bit error rate between Alice and Bob significantly. Yet, we find\nan evenly simple and effective countermeasure to inhibit this and similar\nattacks.\n