232 research outputs found
Secure gated detection scheme for quantum cryptography
Several attacks have been proposed on quantum key distribution systems with
gated single-photon detectors. The attacks involve triggering the detectors
outside the center of the detector gate, and/or using bright illumination to
exploit classical photodiode mode of the detectors. Hence a secure detection
scheme requires two features: The detection events must take place in the
middle of the gate, and the detector must be single-photon sensitive. Here we
present a technique called bit-mapped gating, which is an elegant way to force
the detections in the middle of the detector gate by coupling detection time
and quantum bit error rate. We also discuss how to guarantee single-photon
sensitivity by directly measuring detector parameters. Bit-mapped gating also
provides a simple way to measure the detector blinding parameter in security
proofs for quantum key distribution systems with detector efficiency mismatch,
which up until now has remained a theoretical, unmeasurable quantity. Thus if
single-photon sensitivity can be guaranteed within the gates, a detection
scheme with bit-mapped gating satisfies the assumptions of the current security
proofs.Comment: 7 pages, 3 figure
Full-field implementation of a perfect eavesdropper on a quantum cryptography system
Quantum key distribution (QKD) allows two remote parties to grow a shared
secret key. Its security is founded on the principles of quantum mechanics, but
in reality it significantly relies on the physical implementation.
Technological imperfections of QKD systems have been previously explored, but
no attack on an established QKD connection has been realized so far. Here we
show the first full-field implementation of a complete attack on a running QKD
connection. An installed eavesdropper obtains the entire 'secret' key, while
none of the parameters monitored by the legitimate parties indicate a security
breach. This confirms that non-idealities in physical implementations of QKD
can be fully practically exploitable, and must be given increased scrutiny if
quantum cryptography is to become highly secure.Comment: Revised after editorial and peer-review feedback. This version is
published in Nat. Commun. 8 pages, 6 figures, 1 tabl
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
Superlinear threshold detectors in quantum cryptography
We introduce the concept of a superlinear threshold detector, a detector that
has a higher probability to detect multiple photons if it receives them
simultaneously rather than at separate times. Highly superlinear threshold
detectors in quantum key distribution systems allow eavesdropping the full
secret key without being revealed. Here, we generalize the detector control
attack, and analyze how it performs against quantum key distribution systems
with moderately superlinear detectors. We quantify the superlinearity in
superconducting single-photon detectors based on earlier published data, and
gated avalanche photodiode detectors based on our own measurements. The
analysis shows that quantum key distribution systems using detector(s) of
either type can be vulnerable to eavesdropping. The avalanche photodiode
detector becomes superlinear towards the end of the gate, allowing
eavesdropping using trigger pulses containing less than 120 photons per pulse.
Such an attack would be virtually impossible to catch with an optical power
meter at the receiver entrance.Comment: Rewritten for clearity. Included a discussion on detector dark
counts, a discussion on how to tackle this type of loopholes, and updated
references. 8 pages, 6 figure
Exploitation of Antarctic krill Euphausia superba by three air-breathing predators with contrasting foraging strategies – implications for fisheries feedback management
-SCAR Open Science Conference, Kuala Lumpur 201
Quantum key distribution with delayed privacy amplification and its application to security proof of a two-way deterministic protocol
Privacy amplification (PA) is an essential post-processing step in quantum
key distribution (QKD) for removing any information an eavesdropper may have on
the final secret key. In this paper, we consider delaying PA of the final key
after its use in one-time pad encryption and prove its security. We prove that
the security and the key generation rate are not affected by delaying PA.
Delaying PA has two applications: it serves as a tool for significantly
simplifying the security proof of QKD with a two-way quantum channel, and also
it is useful in QKD networks with trusted relays. To illustrate the power of
the delayed PA idea, we use it to prove the security of a qubit-based two-way
deterministic QKD protocol which uses four states and four encoding operations.Comment: 11 pages, 3 figure
Effect of Intensity Modulator Extinction on Practical Quantum Key Distribution System
We study how the imperfection of intensity modulator effects on the security
of a practical quantum key distribution system. The extinction ratio of the
realistic intensity modulator is considered in our security analysis. We show
that the secret key rate increases, under the practical assumption that the
indeterminable noise introduced by the imperfect intensity modulator can not be
controlled by the eavesdropper.Comment: 6 pages, 5 figures. EPJD accepte
Tight Finite-Key Analysis for Quantum Cryptography
Despite enormous progress both in theoretical and experimental quantum
cryptography, the security of most current implementations of quantum key
distribution is still not established rigorously. One of the main problems is
that the security of the final key is highly dependent on the number, M, of
signals exchanged between the legitimate parties. While, in any practical
implementation, M is limited by the available resources, existing security
proofs are often only valid asymptotically for unrealistically large values of
M. Here, we demonstrate that this gap between theory and practice can be
overcome using a recently developed proof technique based on the uncertainty
relation for smooth entropies. Specifically, we consider a family of
Bennett-Brassard 1984 quantum key distribution protocols and show that security
against general attacks can be guaranteed already for moderate values of M.Comment: 11 pages, 2 figure
Experimental demonstration of phase-remapping attack in a practical quantum key distribution system
Unconditional security proofs of various quantum key distribution (QKD)
protocols are built on idealized assumptions. One key assumption is: the sender
(Alice) can prepare the required quantum states without errors. However, such
an assumption may be violated in a practical QKD system. In this paper, we
experimentally demonstrate a technically feasible "intercept-and-resend" attack
that exploits such a security loophole in a commercial "plug & play" QKD
system. The resulting quantum bit error rate is 19.7%, which is below the
proven secure bound of 20.0% for the BB84 protocol. The attack we utilize is
the phase-remapping attack (C.-H. F. Fung, et al., Phys. Rev. A, 75, 32314,
2007) proposed by our group.Comment: 16 pages, 6 figure
Controlling a superconducting nanowire single-photon detector using tailored bright illumination
We experimentally demonstrate that a superconducting nanowire single-photon
detector is deterministically controllable by bright illumination. We found
that bright light can temporarily make a large fraction of the nanowire length
normally-conductive, can extend deadtime after a normal photon detection, and
can cause a hotspot formation during the deadtime with a highly nonlinear
sensitivity. In result, although based on different physics, the
superconducting detector turns out to be controllable by virtually the same
techniques as avalanche photodiode detectors. As demonstrated earlier, when
such detectors are used in a quantum key distribution system, this allows an
eavesdropper to launch a detector control attack to capture the full secret key
without being revealed by to many errors in the key.Comment: Expanded discussions, updated references. 9 pages, 8 figure
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