260 research outputs found
Sequential Attack with Intensity Modulation on the Differential-Phase-Shift Quantum Key Distribution Protocol
In this paper, we discuss the security of the differential-phase-shift
quantum key distribution (DPSQKD) protocol by introducing an improved version
of the so-called sequential attack, which was originally discussed by Waks et
al. Our attack differs from the original form of the sequential attack in that
the attacker Eve modulates not only the phases but also the amplitude in the
superposition of the single-photon states which she sends to the receiver.
Concentrating especially on the "discretized gaussian" intensity modulation, we
show that our attack is more effective than the individual attack, which had
been the best attack up to present. As a result of this, the recent experiment
with communication distance of 100km reported by Diamanti et al. turns out to
be insecure. Moreover it can be shown that in a practical experimental setup
which is commonly used today, the communication distance achievable by the
DPSQKD protocol is less than 95km.Comment: 6 pages, 2 figure
Advantage of the key relay protocol over secure network coding
The key relay protocol (KRP) plays an important role in improving the
performance and the security of quantum key distribution (QKD) networks. On the
other hand, there is also an existing research field called secure network
coding (SNC), which has similar goal and structure. We here analyze differences
and similarities between the KRP and SNC rigorously. We found, rather
surprisingly, that there is a definite gap in security between the KRP and SNC;
that is, certain KRPs achieve better security than any SNC schemes on the same
graph. We also found that this gap can be closed if we generalize the notion of
SNC by adding free public channels; that is, KRPs are equivalent to SNC schemes
augmented with free public channels.Comment: 10 pages, 11 figure
Implementable Quantum Bit-String Commitment Protocol
Quantum bit-string commitment[A.Kent, Phys.Rev.Lett., 90, 237901 (2003)] or
QBSC is a variant of bit commitment (BC). In this paper, we propose a new QBSC
protocol that can be implemented using currently available technology, and
prove its security under the same security criteria as discussed by Kent. QBSC
is a generalization of BC, but has slightly weaker requirements, and our
proposed protocol is not intended to break the no-go theorem of quantum BC.Comment: To appear in Phys. Rev. A., 9 pages, 2 figure
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