Real-time monitoring of single-photon detectors against eavesdropping in quantum key distribution systems

T. Ferreira da Silva, G. B. Xavier, G. P. Temporao and J. P. von der Weid


By employing real-time monitoring of single-photon avalanche
photodiodes we demonstrate how two types of practical eavesdropping
strategies, the after-gate and time-shift attacks, may be detected. Both
attacks are identified with the detectors operating without any special
modifications, making this proposal well suited for real-world applications.
The monitoring system is based on accumulating statistics of the times
between consecutive detection events, and extracting the afterpulse and
overall efficiency of the detectors in real-time using mathematical models
fit to the measured data. We are able to directly observe changes in the
afterpulse probabilities generated from the after-gate and faint after-gate
attacks, as well as different timing signatures in the time-shift attack. We
also discuss the applicability of our scheme to other general blinding