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Hacking commercial quantum cryptography systems by tailored bright illumination


The peculiar properties of quantum mechanics allow two remote parties to communicate a private, secret key, which is protected from eavesdropping by the laws of physics1,2,3,4. So-called quantum key distribution (QKD) implementations always rely on detectors to measure the relevant quantum property of single photons5. Here we demonstrate experimentally that the detectors in two commercially available QKD systems can be fully remote-controlled using specially tailored bright illumination. This makes it possible to tracelessly acquire the full secret key; we propose an eavesdropping apparatus built from off-the-shelf components. The loophole is likely to be present in most QKD systems using avalanche photodiodes to detect single photons. We believe that our findings are crucial for strengthening the security of practical QKD, by identifying and patching technological deficiencies.

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Figure 1: APD as a single-photon detector.
Figure 2: How Eve's trigger pulses are detected by Bob.
Figure 3: Bias voltage at T1 versus c.w. laser power for Clavis2.
Figure 4: Detector control.
Figure 5: Proposed plug-and-play Eve.


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This work was supported by the Research Council of Norway (grant no. 180439/V30). The authors acknowledge the overall cooperation and assistance of the Max Planck Institute for the Science of Light, Erlangen, and G. Leuchs personally. L.L. and V.M. thank the Group of Applied Physics at the University of Geneva, ID Quantique and armasuisse Science and Technology for their hospitality, discussions, cooperation and loan of equipment. The Service of Radiology of the Cantonal Hospital of Geneva is thanked for their quick help in revealing the internal layers in the multilayer printed circuit board of a commercial detector.

Author information




V.M. conceived the idea and planned the study. L.L. and V.M. conducted the Clavis2 experiment with the help of C. Wiechers, D.E. and C. Wittmann. L.L. and V.M. conducted the QPN 5505 experiment. L.L. and J.S. wrote the paper and Supplementary information, with input from all authors. J.S. and V.M. supervised the project.

Corresponding author

Correspondence to Lars Lydersen.

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The authors declare no competing financial interests.

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Lydersen, L., Wiechers, C., Wittmann, C. et al. Hacking commercial quantum cryptography systems by tailored bright illumination. Nature Photon 4, 686–689 (2010).

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