2,174 research outputs found
Limitations on Quantum Key Repeaters
A major application of quantum communication is the distribution of entangled
particles for use in quantum key distribution (QKD). Due to noise in the
communication line, QKD is in practice limited to a distance of a few hundred
kilometres, and can only be extended to longer distances by use of a quantum
repeater, a device which performs entanglement distillation and quantum
teleportation. The existence of noisy entangled states that are undistillable
but nevertheless useful for QKD raises the question of the feasibility of a
quantum key repeater, which would work beyond the limits of entanglement
distillation, hence possibly tolerating higher noise levels than existing
protocols. Here we exhibit fundamental limits on such a device in the form of
bounds on the rate at which it may extract secure key. As a consequence, we
give examples of states suitable for QKD but unsuitable for the most general
quantum key repeater protocol.Comment: 11+38 pages, 4 figures, Statements for exact p-bits weakened as
non-locking bound on measured relative entropy distance contained an erro
Networks based on QKD and weakly trusted repeaters
We study how to use quantum key distribution (QKD) in common optical network infrastructures and propose a method to overcome its distance limitations. QKD is the first technology offering information theoretic secret-key distribution that relies only on the fundamental principles of quantum physics. Point-to-point QKD devices have reached a mature industrial state; however, these devices are severely limited in distance, since signals at the quantum level (e.g. single photons) are highly affected by the losses in the communication channel and intermediate devices. To overcome this limitation, intermediate nodes (i.e. repeaters) are used. Both, quantum-regime and trusted, classical, repeaters have been proposed in the QKD literature, but only the latter can be implemented in practice. As a novelty, we propose here a new QKD network model based on the use of not fully trusted intermediate nodes, referred as weakly trusted repeaters. This approach forces the attacker to simultaneously break several paths to get access to the exchanged key, thus improving significantly the security of the network. We formalize the model using network codes and provide real scenarios that allow users to exchange secure keys over metropolitan optical networks using only passive components
Secure Optical Networks Based on Quantum Key Distribution and Weakly Trusted Repeaters
In this paper we explore how recent technologies can improve the security of
optical networks. In particular, we study how to use quantum key distribution
(QKD) in common optical network infrastructures and propose a method to
overcome its distance limitations. QKD is the first technology offering
information theoretic secret-key distribution that relies only on the
fundamental principles of quantum physics. Point-to-point QKD devices have
reached a mature industrial state; however, these devices are severely limited
in distance, since signals at the quantum level (e.g. single photons) are
highly affected by the losses in the communication channel and intermediate
devices. To overcome this limitation, intermediate nodes (i.e. repeaters) are
used. Both, quantum-regime and trusted, classical, repeaters have been proposed
in the QKD literature, but only the latter can be implemented in practice. As a
novelty, we propose here a new QKD network model based on the use of not fully
trusted intermediate nodes, referred as weakly trusted repeaters. This approach
forces the attacker to simultaneously break several paths to get access to the
exchanged key, thus improving significantly the security of the network. We
formalize the model using network codes and provide real scenarios that allow
users to exchange secure keys over metropolitan optical networks using only
passive components. Moreover, the theoretical framework allows to extend these
scenarios not only to accommodate more complex trust constraints, but also to
consider robustness and resiliency constraints on the network.Comment: 11 pages, 13 figure
Distributed Relay Protocol for Probabilistic Information-Theoretic Security in a Randomly-Compromised Network
We introduce a simple, practical approach with probabilistic
information-theoretic security to mitigate one of quantum key distribution's
major limitations: the short maximum transmission distance (~200 km) possible
with present day technology. Our scheme uses classical secret sharing
techniques to allow secure transmission over long distances through a network
containing randomly-distributed compromised nodes. The protocol provides
arbitrarily high confidence in the security of the protocol, with modest
scaling of resource costs with improvement of the security parameter. Although
some types of failure are undetectable, users can take preemptive measures to
make the probability of such failures arbitrarily small.Comment: 12 pages, 2 figures; added proof of verification sub-protocol, minor
correction
Hamiltonians for one-way quantum repeaters
Quantum information degrades over distance due to the unavoidable
imperfections of the transmission channels, with loss as the leading factor.
This simple fact hinders quantum communication, as it relies on propagating
quantum systems. A solution to this issue is to introduce quantum repeaters at
regular intervals along a lossy channel, to revive the quantum signal. In this
work we study unitary one-way quantum repeaters, which do not need to perform
measurements and do not require quantum memories, and are therefore
considerably simpler than other schemes. We introduce and analyze two methods
to construct Hamiltonians that generate a repeater interaction that can beat
the fundamental repeaterless key rate bound even in the presence of an
additional coupling loss, with signals that contain only a handful of photons.
The natural evolution of this work will be to approximate a repeater
interaction by combining simple optical elements.Comment: 8 pages, 3 figure
The Case for Quantum Key Distribution
Quantum key distribution (QKD) promises secure key agreement by using quantum
mechanical systems. We argue that QKD will be an important part of future
cryptographic infrastructures. It can provide long-term confidentiality for
encrypted information without reliance on computational assumptions. Although
QKD still requires authentication to prevent man-in-the-middle attacks, it can
make use of either information-theoretically secure symmetric key
authentication or computationally secure public key authentication: even when
using public key authentication, we argue that QKD still offers stronger
security than classical key agreement.Comment: 12 pages, 1 figure; to appear in proceedings of QuantumComm 2009
Workshop on Quantum and Classical Information Security; version 2 minor
content revision
- …