4,992 research outputs found
Fundamental finite key limits for information reconciliation in quantum key distribution
The security of quantum key distribution protocols is guaranteed by the laws of quantum mechanics. However, a precise analysis of the security properties requires tools from both classical cryptography and information theory. Here, we employ recent results in non-asymptotic classical information theory to show that information reconciliation imposes fundamental limitations on the amount of secret key that can be extracted in the finite key regime. In particular, we find that an often used approximation for the information leakage during one-way information reconciliation is flawed and we propose an improved estimate
Fundamental Finite Key Limits for One-Way Information Reconciliation in Quantum Key Distribution
The security of quantum key distribution protocols is guaranteed by the laws
of quantum mechanics. However, a precise analysis of the security properties
requires tools from both classical cryptography and information theory. Here,
we employ recent results in non-asymptotic classical information theory to show
that one-way information reconciliation imposes fundamental limitations on the
amount of secret key that can be extracted in the finite key regime. In
particular, we find that an often used approximation for the information
leakage during information reconciliation is not generally valid. We propose an
improved approximation that takes into account finite key effects and
numerically test it against codes for two probability distributions, that we
call binary-binary and binary-Gaussian, that typically appear in quantum key
distribution protocols
Complete elimination of information leakage in continuous-variable quantum communication channels
In all lossy communication channels realized to date, information is
inevitably leaked to a potential eavesdropper. Here we present a communication
protocol that does not allow for any information leakage to a potential
eavesdropper in a purely lossy channel. By encoding information into a
restricted Gaussian alphabet of squeezed states we show, both theoretically and
experimentally, that the Holevo information between the eavesdropper and the
intended recipient can be exactly zero in a purely lossy channel while
minimized in a noisy channel. This result is of fundamental interest, but might
also have practical implications in extending the distance of secure quantum
key distribution.Comment: 9 pages, 5 figure
Continuous-variable quantum enigma machines for long-distance key distribution
Quantum physics allows for unconditionally secure communication through
insecure communication channels. The achievable rates of quantum-secured
communication are fundamentally limited by the laws of quantum physics and in
particular by the properties of entanglement. For a lossy communication line,
this implies that the secret-key generation rate vanishes at least
exponentially with the communication distance. We show that this fundamental
limitation can be violated in a realistic scenario where the eavesdropper can
store quantum information for only a finite, yet arbitrarily long, time. We
consider communication through a lossy bononic channel (modeling linear loss in
optical fibers) and we show that it is in principle possible to achieve a
constant rate of key generation of one bit per optical mode over arbitrarily
long communication distances.Comment: 13 pages. V2: new title, new result on active attacks, increased
rigour in the security proo
Squeezing-enhanced quantum key distribution over atmospheric channels
We propose the Gaussian continuous-variable quantum key distribution using
squeezed states in the composite channels including atmospheric propagation
with transmittance fluctuations. We show that adjustments of signal modulation
and use of optimal feasible squeezing can be sufficient to significantly
overcome the coherent-state protocol and drastically improve the performance of
quantum key distribution in atmospheric channels, also in the presence of
additional attenuating and noisy channels. Furthermore, we consider examples of
atmospheric links of different lengths, and show that optimization of both
squeezing and modulation is crucial for reduction of protocol downtime and
increase of secure atmospheric channel distance. Our results demonstrate
unexpected advantage of fragile squeezed states of light in the free-space
quantum key distribution applicable in daylight and stable against atmospheric
turbulence.Comment: 10 pages, 3 figure
Gaussian Operations and Privacy
We consider the possibilities offered by Gaussian states and operations for
two honest parties, Alice and Bob, to obtain privacy against a third
eavesdropping party, Eve. We first extend the security analysis of the protocol
proposed in M. Navascues et al., Phys. Rev. Lett. 94, 010502 (2005). Then, we
prove that a generalized version of this protocol does not allow to distill a
secret key out of bound entangled Gaussian states
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