4,854 research outputs found
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 physics. So-called quantum key distribution (QKD) implementations
always rely on detectors to measure the relevant quantum property of single
photons. 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 of
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.Comment: Revised version, rewritten for clarity. 5 pages, 5 figures. To
download the Supplementary information (which is in open access), go to the
journal web site at http://dx.doi.org/10.1038/nphoton.2010.21
Boosting up quantum key distribution by learning statistics of practical single photon sources
We propose a simple quantum-key-distribution (QKD) scheme for practical
single photon sources (SPSs), which works even with a moderate suppression of
the second-order correlation of the source. The scheme utilizes a
passive preparation of a decoy state by monitoring a fraction of the signal via
an additional beam splitter and a detector at the sender's side to monitor
photon number splitting attacks. We show that the achievable distance increases
with the precision with which the sub-Poissonian tendency is confirmed in
higher photon number distribution of the source, rather than with actual
suppression of the multi-photon emission events. We present an example of the
secure key generation rate in the case of a poor SPS with , in
which no secure key is produced with the conventional QKD scheme, and show that
learning the photon-number distribution up to several numbers is sufficient for
achieving almost the same achievable distance as that of an ideal SPS.Comment: 11 pages, 3 figures; published version in New J. Phy
Trojan-horse attacks threaten the security of practical quantum cryptography
A quantum key distribution 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 Bob's secret basis choice, and
thus the raw key bit in the Scarani-Ac\'in-Ribordy-Gisin 2004 protocol, with
higher than 90% probability. This would clearly breach the security of the
cryptosystem. Unfortunately in Clavis2 Eve's bright pulses have a side effect
of causing high level of afterpulsing in Bob's single-photon detectors,
resulting in a high quantum bit error rate that effectively protects this
system from our attack. However, in a Clavis2-like system equipped with
detectors with less-noisy but realistic characteristics, an attack strategy
with positive leakage of the key would exist. We confirm this by a numerical
simulation. Both the eavesdropping setup and strategy can be generalized to
attack most of the current QKD systems, especially if they lack proper
safeguards. We also propose countermeasures to prevent such attacks.Comment: 22 pages including appendix and references, 6+2 figure
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