5,649 research outputs found
Effective Privacy Amplification for Secure Classical Communications
We study the practical effectiveness of privacy amplification for classical
key-distribution schemes. We find that in contrast to quantum key distribution
schemes, the high fidelity of the raw key generated in classical systems allow
the users to always sift a secure shorter key if they have an upper bound on
the eavesdropper probability to correctly guess the exchanged key-bits. The
number of privacy amplification iterations needed to achieve information leak
of 10^-8 in existing classical communicators is 2 or 3 resulting in a
corresponding slowdown 4 to 8. We analyze the inherent tradeoff between the
number of iterations and the security of the raw key. This property which is
unique to classical key distribution systems render them highly useful for
practical, especially for noisy channels where sufficiently low quantum bit
error ratios are difficult to achieve.Comment: 11 pages, 3 figure
Modified Bennett-Brassard 1984 Quantum Key Distribution With Two-way Classical Communications
The quantum key distribution protocol without public announcement of bases is
equipped with a two-way classical communication symmetric entanglement
purification protocol. This modified key distribution protocol is
unconditionally secure and has a higher tolerable error rate of 20%, which is
higher than previous scheme without public announcement of bases.Comment: 5 pages. To appear in Physical Review
Experimental quantum key distribution with simulated ground-to-satellite photon losses and processing limitations
Quantum key distribution (QKD) has the potential to improve communications
security by offering cryptographic keys whose security relies on the
fundamental properties of quantum physics. The use of a trusted quantum
receiver on an orbiting satellite is the most practical near-term solution to
the challenge of achieving long-distance (global-scale) QKD, currently limited
to a few hundred kilometers on the ground. This scenario presents unique
challenges, such as high photon losses and restricted classical data
transmission and processing power due to the limitations of a typical satellite
platform. Here we demonstrate the feasibility of such a system by implementing
a QKD protocol, with optical transmission and full post-processing, in the
high-loss regime using minimized computing hardware at the receiver. Employing
weak coherent pulses with decoy states, we demonstrate the production of secure
key bits at up to 56.5 dB of photon loss. We further illustrate the feasibility
of a satellite uplink by generating secure key while experimentally emulating
the varying channel losses predicted for realistic low-Earth-orbit satellite
passes at 600 km altitude. With a 76 MHz source and including finite-size
analysis, we extract 3374 bits of secure key from the best pass. We also
illustrate the potential benefit of combining multiple passes together: while
one suboptimal "upper-quartile" pass produces no finite-sized key with our
source, the combination of three such passes allows us to extract 165 bits of
secure key. Alternatively, we find that by increasing the signal rate to 300
MHz it would be possible to extract 21570 bits of secure finite-sized key in
just a single upper-quartile pass.Comment: 12 pages, 7 figures, 2 table
Finite-Block-Length Analysis in Classical and Quantum Information Theory
Coding technology is used in several information processing tasks. In
particular, when noise during transmission disturbs communications, coding
technology is employed to protect the information. However, there are two types
of coding technology: coding in classical information theory and coding in
quantum information theory. Although the physical media used to transmit
information ultimately obey quantum mechanics, we need to choose the type of
coding depending on the kind of information device, classical or quantum, that
is being used. In both branches of information theory, there are many elegant
theoretical results under the ideal assumption that an infinitely large system
is available. In a realistic situation, we need to account for finite size
effects. The present paper reviews finite size effects in classical and quantum
information theory with respect to various topics, including applied aspects
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