Implementation of an attack scheme on a practical QKD system

We report on an experimental implementation of an attack of a practical quantum key distribution system [1], based on a vulnerability of single photon detectors [2]. An intercept/resend-like attack has been carried out which revealed 100\% of the raw key generated between the legitimate communication partners. No increase of the error ratio was observed, which is usually considered a reliable witness for any eavesdropping attempt. We also present an experiment which shows that this attack is not revealed by key distribution protocols probing for eavesdroppers by testing a Bell inequality {[3]}, and discuss implications for practical quantum key distribution.\\[4pt] [1] I. Marcikic, A. Lamas-Linares, C. Kurtsiefer, Appl. Phys. Lett. 89, 101122 (2006); {[2]} V. Makarov, New J. Phys. 11, 065003 (2009); {[3]} A. Ling et al., Phys. Rev. A 78, 020301(R), (2008)