17 research outputs found
Optimal ratio between phase basis and bit basis in QKD
In the original BB84 protocol, the bit basis and the phase basis are used
with equal probability. Lo et al (J. of Cryptology, 18, 133-165 (2005))
proposed to modify the ratio between the two bases by increasing the final key
generation rate. However, the optimum ratio has not been derived. In this
letter, in order to examine this problem, the ratio between the two bases is
optimized for exponential constraints given Eve's information
distinguishability and the final error probability
Rate Compatible Protocol for Information Reconciliation: An application to QKD
Information Reconciliation is a mechanism that allows to weed out the
discrepancies between two correlated variables. It is an essential component in
every key agreement protocol where the key has to be transmitted through a
noisy channel. The typical case is in the satellite scenario described by
Maurer in the early 90's. Recently the need has arisen in relation with Quantum
Key Distribution (QKD) protocols, where it is very important not to reveal
unnecessary information in order to maximize the shared key length. In this
paper we present an information reconciliation protocol based on a rate
compatible construction of Low Density Parity Check codes. Our protocol
improves the efficiency of the reconciliation for the whole range of error
rates in the discrete variable QKD context. Its adaptability together with its
low interactivity makes it specially well suited for QKD reconciliation
Key rate available from mismatched mesurements in the BB84 protocol and the uncertainty principle
We consider the mismatched measurements in the BB84 quantum key distribution
protocol, in which measuring bases are different from transmitting bases. We
give a lower bound on the amount of a secret key that can be extracted from the
mismatched measurements. Our lower bound shows that we can extract a secret key
from the mismatched measurements with certain quantum channels, such as the
channel over which the Hadamard matrix is applied to each qubit with high
probability. Moreover, the entropic uncertainty principle implies that one
cannot extract the secret key from both matched measurements and mismatched
ones simultaneously, when we use the standard information reconciliation and
privacy amplification procedure.Comment: 5 pages, no figure, ieice.cls. Title was changed from version 1. To
appear in IEICE Trans. Fundamentals (http://ietfec.oxfordjournals.org/), vol.
E91-A, no. 10, Oct. 200
Key rate available from mismatched mesurements in the BB84 protocol and the uncertainty principle
We consider the mismatched measurements in the BB84 quantum key distribution
protocol, in which measuring bases are different from transmitting bases. We
give a lower bound on the amount of a secret key that can be extracted from the
mismatched measurements. Our lower bound shows that we can extract a secret key
from the mismatched measurements with certain quantum channels, such as the
channel over which the Hadamard matrix is applied to each qubit with high
probability. Moreover, the entropic uncertainty principle implies that one
cannot extract the secret key from both matched measurements and mismatched
ones simultaneously, when we use the standard information reconciliation and
privacy amplification procedure.Comment: 5 pages, no figure, ieice.cls. Title was changed from version 1. To
appear in IEICE Trans. Fundamentals (http://ietfec.oxfordjournals.org/), vol.
E91-A, no. 10, Oct. 200
Fundamental limits on key rates in device-independent quantum key distribution
In this paper, we introduce intrinsic non-locality as a quantifier for Bell
non-locality, and we prove that it satisfies certain desirable properties such
as faithfulness, convexity, and monotonicity under local operations and shared
randomness. We then prove that intrinsic non-locality is an upper bound on the
secret-key-agreement capacity of any device-independent protocol conducted
using a device characterized by a correlation . We also prove that intrinsic
steerability is an upper bound on the secret-key-agreement capacity of any
semi-device-independent protocol conducted using a device characterized by an
assemblage . We also establish the faithfulness of intrinsic
steerability and intrinsic non-locality. Finally, we prove that intrinsic
non-locality is bounded from above by intrinsic steerability.Comment: 44 pages, 4 figures, final version accepted for publication in New
Journal of Physic
Secret Key Agreement: General Capacity and Second-Order Asymptotics
We revisit the problem of secret key agreement using interactive public
communication for two parties and propose a new secret key agreement protocol.
The protocol attains the secret key capacity for general observations and
attains the second-order asymptotic term in the maximum length of a secret key
for independent and identically distributed observations. In contrast to the
previously suggested secret key agreement protocols, the proposed protocol uses
interactive communication. In fact, the standard one-way communication protocol
used prior to this work fails to attain the asymptotic results above. Our
converse proofs rely on a recently established upper bound for secret key
lengths. Both our lower and upper bounds are derived in a single-shot setup and
the asymptotic results are obtained as corollaries