Trojan-horse attacks threaten the security of practical quantum cryptography

@article{Jain2014TrojanhorseAT,
  title={Trojan-horse attacks threaten the security of practical quantum cryptography},
  author={Nitin Jain and Elena Anisimova and Imran Khan and Vadim Makarov and Christoph Marquardt and Gerd Leuchs},
  journal={New Journal of Physics},
  year={2014},
  volume={16}
}
A quantum key distribution (QKD) system may be probed by an eavesdropper Eve by sending in bright light from the quantum channel and analyzing the back-reflections. We propose and experimentally demonstrate a setup for mounting such a Trojan-horse attack. We show it in operation against the quantum cryptosystem Clavis2 from ID Quantique, as a proof-of-principle. With just a few back-reflected photons, Eve discerns Bobʼs (secret) basis choice, and thus the raw key bit in the Scarani–Acín–Ribordy… 

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