533 research outputs found
Which verification qubits perform best for secure communication in noisy channel?
In secure quantum communication protocols, a set of single qubits prepared
using 2 or more mutually unbiased bases or a set of -qubit ()
entangled states of a particular form are usually used to form a verification
string which is subsequently used to detect traces of eavesdropping. The qubits
that form a verification string are referred to as decoy qubits, and there
exists a large set of different quantum states that can be used as decoy
qubits. In the absence of noise, any choice of decoy qubits provides equivalent
security. In this paper, we examine such equivalence for noisy environment
(e.g., in amplitude damping, phase damping, collective dephasing and collective
rotation noise channels) by comparing the decoy-qubit assisted schemes of
secure quantum communication that use single qubit states as decoy qubits with
the schemes that use entangled states as decoy qubits. Our study reveals that
the single qubit assisted scheme perform better in some noisy environments,
while some entangled qubits assisted schemes perform better in other noisy
environments. Specifically, single qubits assisted schemes perform better in
amplitude damping and phase damping noisy channels, whereas a few
Bell-state-based decoy schemes are found to perform better in the presence of
the collective noise. Thus, if the kind of noise present in a communication
channel (i.e., the characteristics of the channel) is known or measured, then
the present study can provide the best choice of decoy qubits required for
implementation of schemes of secure quantum communication through that channel.Comment: 11 pages, 4 figure
A comparative study of protocols for secure quantum communication under noisy environment: single-qubit-based protocols versus entangled-state-based protocols
The effect of noise on various protocols of secure quantum communication has
been studied. Specifically, we have investigated the effect of amplitude
damping, phase damping, squeezed generalized amplitude damping, Pauli type as
well as various collective noise models on the protocols of quantum key
distribution, quantum key agreement,quantum secure direct quantum communication
and quantum dialogue. From each type of protocol of secure quantum
communication, we have chosen two protocols for our comparative study; one
based on single qubit states and the other one on entangled states. The
comparative study reported here has revealed that single-qubit-based schemes
are generally found to perform better in the presence of amplitude damping,
phase damping, squeezed generalized amplitude damping noises, while
entanglement-based protocols turn out to be preferable in the presence of
collective noises. It is also observed that the effect of noise entirely
depends upon the number of rounds of quantum communication involved in a scheme
of quantum communication. Further, it is observed that squeezing, a completely
quantum mechanical resource present in the squeezed generalized amplitude
channel, can be used in a beneficial way as it may yield higher fidelity
compared to the corresponding zero squeezing case.Comment: 23 pages 7 figure
Quantum e-commerce: A comparative study of possible protocols for online shopping and other tasks related to e-commerce
A set of quantum protocols for online shopping is proposed and analyzed to
establish that it is possible to perform secure online shopping using different
types of quantum resources. Specifically, a single photon based, a Bell state
based and two 3-qubit entangled state based quantum online shopping schemes are
proposed. The Bell state based scheme, being a completely orthogonal state
based protocol, is fundamentally different from the earlier proposed schemes
which were based on conjugate coding. One of the 3-qubit entangled state based
scheme is build on the principle of entanglement swapping which enables us to
accomplish the task without transmission of the message encoded qubits through
the channel. Possible ways of generalizing the entangled state based schemes
proposed here to the schemes which use multiqubit entangled states is also
discussed. Further, all the proposed protocols are shown to be free from the
limitations of the recently proposed protocol of Huang et al. (Quantum Inf.
Process. 14, 2211-2225, 2015) which allows the buyer (Alice) to change her
order at a later time (after initially placing the order and getting it
authenticated by the controller). The proposed schemes are also compared with
the existing schemes using qubit efficiency.Comment: It's shown that quantum e-commerce is not a difficult task, and it
can be done in various way
Kak's three-stage protocol of secure quantum communication revisited: Hitherto unknown strengths and weaknesses of the protocol
Kak's three-stage protocol for quantum key distribution is revisited with
special focus on its hitherto unknown strengths and weaknesses. It is shown
that this protocol can be used for secure direct quantum communication.
Further, the implementability of this protocol in the realistic situation is
analyzed by considering various Markovian noise models. It is found that the
Kak's protocol and its variants in their original form can be implemented only
in a restricted class of noisy channels, where the protocols can be transformed
to corresponding protocols based on logical qubits in decoherence free
subspace. Specifically, it is observed that Kak's protocol can be implemented
in the presence of collective rotation and collective dephasing noise, but
cannot be implemented in its original form in the presence of other types of
noise, like amplitude damping and phase damping noise. Further, the performance
of the protocol in the noisy environment is quantified by computing average
fidelity under various noise models, and subsequently a set of preferred states
for secure communication in noisy environment have also been identified.Comment: Kak's protocol is not suitable for quantum cryptography in presence
of nois
Quantum Cryptography Beyond Quantum Key Distribution
Quantum cryptography is the art and science of exploiting quantum mechanical
effects in order to perform cryptographic tasks. While the most well-known
example of this discipline is quantum key distribution (QKD), there exist many
other applications such as quantum money, randomness generation, secure two-
and multi-party computation and delegated quantum computation. Quantum
cryptography also studies the limitations and challenges resulting from quantum
adversaries---including the impossibility of quantum bit commitment, the
difficulty of quantum rewinding and the definition of quantum security models
for classical primitives. In this review article, aimed primarily at
cryptographers unfamiliar with the quantum world, we survey the area of
theoretical quantum cryptography, with an emphasis on the constructions and
limitations beyond the realm of QKD.Comment: 45 pages, over 245 reference
Experimental quantum key distribution with finite-key security analysis for noisy channels
In quantum key distribution implementations, each session is typically chosen
long enough so that the secret key rate approaches its asymptotic limit.
However, this choice may be constrained by the physical scenario, as in the
perspective use with satellites, where the passage of one terminal over the
other is restricted to a few minutes. Here we demonstrate experimentally the
extraction of secure keys leveraging an optimal design of the
prepare-and-measure scheme, according to recent finite-key theoretical
tight-bounds. The experiment is performed in different channel conditions, and
assuming two distinct attack models: individual attacks, or general quantum
attacks. The request on the number of exchanged qubits is then obtained as a
function of the key size and of the ambient quantum bit error rate. The results
indicate that viable conditions for effective symmetric, and even one-time-pad,
cryptography are achievable.Comment: 20 pages, 4 figure
Revisiting Deniability in Quantum Key Exchange via Covert Communication and Entanglement Distillation
We revisit the notion of deniability in quantum key exchange (QKE), a topic
that remains largely unexplored. In the only work on this subject by Donald
Beaver, it is argued that QKE is not necessarily deniable due to an
eavesdropping attack that limits key equivocation. We provide more insight into
the nature of this attack and how it extends to other constructions such as QKE
obtained from uncloneable encryption. We then adopt the framework for quantum
authenticated key exchange, developed by Mosca et al., and extend it to
introduce the notion of coercer-deniable QKE, formalized in terms of the
indistinguishability of real and fake coercer views. Next, we apply results
from a recent work by Arrazola and Scarani on covert quantum communication to
establish a connection between covert QKE and deniability. We propose DC-QKE, a
simple deniable covert QKE protocol, and prove its deniability via a reduction
to the security of covert QKE. Finally, we consider how entanglement
distillation can be used to enable information-theoretically deniable protocols
for QKE and tasks beyond key exchange.Comment: 16 pages, published in the proceedings of NordSec 201
Semi-quantum communication: Protocols for key agreement, controlled secure direct communication and dialogue
Semi-quantum protocols that allow some of the users to remain classical are
proposed for a large class of problems associated with secure communication and
secure multiparty computation. Specifically, first time semi-quantum protocols
are proposed for key agreement, controlled deterministic secure communication
and dialogue, and it is shown that the semi-quantum protocols for controlled
deterministic secure communication and dialogue can be reduced to semi-quantum
protocols for e-commerce and private comparison (socialist millionaire
problem), respectively. Complementing with the earlier proposed semi-quantum
schemes for key distribution, secret sharing and deterministic secure
communication, set of schemes proposed here and subsequent discussions have
established that almost every secure communication and computation tasks that
can be performed using fully quantum protocols can also be performed in
semi-quantum manner. Further, it addresses a fundamental question in context of
a large number problems- how much quantumness is (how many quantum parties are)
required to perform a specific secure communication task? Some of the proposed
schemes are completely orthogonal-state-based, and thus, fundamentally
different from the existing semi-quantum schemes that are
conjugate-coding-based. Security, efficiency and applicability of the proposed
schemes have been discussed with appropriate importance.Comment: 19 pages 1 figur
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