61 research outputs found
Experimental demonstration of long-distance continuous-variable quantum key distribution
Distributing secret keys with information-theoretic security is arguably one
of the most important achievements of the field of quantum information
processing and communications. The rapid progress in this field has enabled
quantum key distribution (QKD) in real-world conditions and commercial devices
are now readily available. QKD systems based on continuous variables present
the major advantage that they only require standard telecommunication
technology, and in particular, that they do not use photon counters. However,
these systems were considered up till now unsuitable for long-distance
communication. Here, we overcome all previous limitations and demonstrate for
the first time continuous-variable quantum key distribution over 80 km of
optical fibre. The demonstration includes all aspects of a practical scenario,
with real-time generation of secret keys, stable operation in a regular
environment, and use of finite-size data blocks for secret information
computation and key distillation. Our results correspond to an implementation
guaranteeing the strongest level of security for QKD reported to date for such
long distances and pave the way to practical applications of secure quantum
communications
Preventing Calibration Attacks on the Local Oscillator in Continuous-Variable Quantum Key Distribution
Establishing an information-theoretic secret key between two parties using a
quantum key distribution (QKD) system is only possible when an accurate
characterization of the quantum channel and proper device calibration routines
are combined. Indeed, security loopholes due to inappropriate calibration
routines have been shown for discrete-variable QKD. Here, we propose and
provide experimental evidence of an attack targeting the local oscillator
calibration routine of a continuous-variable QKD system. The attack consists in
manipulating the classical local oscillator pulses during the QKD run in order
to modify the clock pulses used at the detection stage. This allows the
eavesdropper to bias the shot noise estimation usually performed using a
calibrated relationship. This loophole can be used to perform successfully an
intercept-resend attack. We characterize the loophole and suggest possible
countermeasures.Comment: 7 pages, 6 figure
Analysis of Imperfections in Practical Continuous-Variable Quantum Key Distribution
As quantum key distribution becomes a mature technology, it appears clearly
that some assumptions made in the security proofs cannot be justified in
practical implementations. This might open the door to possible side-channel
attacks. We examine several discrepancies between theoretical models and
experimental setups in the case of continuous-variable quantum key
distribution. We study in particular the impact of an imperfect modulation on
the security of Gaussian protocols and show that approximating the theoretical
Gaussian modulation with a discrete one is sufficient in practice. We also
address the issue of properly calibrating the detection setup, and in
particular the value of the shot noise. Finally, we consider the influence of
phase noise in the preparation stage of the protocol and argue that taking this
noise into account can improve the secret key rate because this source of noise
is not controlled by the eavesdropper.Comment: 4 figure
Field Test of Classical Symmetric Encryption with Continuous Variable Quantum Key Distribution
We report on the design and performance of a point-to-point classical
symmetric encryption link with fast key renewal provided by a Continuous
Variable Quantum Key Distribution (CVQKD) system. Our system was operational
and able to encrypt point-to-point communications during more than six months,
from the end of July 2010 until the beginning of February 2011. This field test
was the first demonstration of the reliability of a CVQKD system over a long
period of time in a server room environment. This strengthens the potential of
CVQKD for information technology security infrastructure deployments
Long Distance Continuous-Variable Quantum Key Distribution with a Gaussian Modulation
We designed high-efficiency error correcting codes allowing to extract an
errorless secret key in a continuous-variable quantum key distribution protocol
using a Gaussian modulation of coherent states and a homodyne detection. These
codes are available for a wide range of signal-to-noise ratios on an AWGN
channel with a binary modulation and can be combined with a multidimensional
reconciliation method proven secure against arbitrary collective attacks. This
improved reconciliation procedure considerably extends the secure range of a
continuous-variable quantum key distribution with a Gaussian modulation, giving
a secret key rate of about 10^{-3} bit per pulse at a distance of 120 km for
reasonable physical parameters.Comment: 8 pages, 5 figures, 5 table
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