4,576 research outputs found
Repeat-Accumulate Codes for Reconciliation in Continuous Variable Quantum Key Distribution
This paper investigates the design of low-complexity error correction codes
for the verification step in continuous variable quantum key distribution
(CVQKD) systems. We design new coding schemes based on quasi-cyclic
repeat-accumulate codes which demonstrate good performances for CVQKD
reconciliation
Principles of Physical Layer Security in Multiuser Wireless Networks: A Survey
This paper provides a comprehensive review of the domain of physical layer
security in multiuser wireless networks. The essential premise of
physical-layer security is to enable the exchange of confidential messages over
a wireless medium in the presence of unauthorized eavesdroppers without relying
on higher-layer encryption. This can be achieved primarily in two ways: without
the need for a secret key by intelligently designing transmit coding
strategies, or by exploiting the wireless communication medium to develop
secret keys over public channels. The survey begins with an overview of the
foundations dating back to the pioneering work of Shannon and Wyner on
information-theoretic security. We then describe the evolution of secure
transmission strategies from point-to-point channels to multiple-antenna
systems, followed by generalizations to multiuser broadcast, multiple-access,
interference, and relay networks. Secret-key generation and establishment
protocols based on physical layer mechanisms are subsequently covered.
Approaches for secrecy based on channel coding design are then examined, along
with a description of inter-disciplinary approaches based on game theory and
stochastic geometry. The associated problem of physical-layer message
authentication is also introduced briefly. The survey concludes with
observations on potential research directions in this area.Comment: 23 pages, 10 figures, 303 refs. arXiv admin note: text overlap with
arXiv:1303.1609 by other authors. IEEE Communications Surveys and Tutorials,
201
Universal Hashing for Information Theoretic Security
The information theoretic approach to security entails harnessing the
correlated randomness available in nature to establish security. It uses tools
from information theory and coding and yields provable security, even against
an adversary with unbounded computational power. However, the feasibility of
this approach in practice depends on the development of efficiently
implementable schemes. In this article, we review a special class of practical
schemes for information theoretic security that are based on 2-universal hash
families. Specific cases of secret key agreement and wiretap coding are
considered, and general themes are identified. The scheme presented for wiretap
coding is modular and can be implemented easily by including an extra
pre-processing layer over the existing transmission codes.Comment: Corrected an error in the proof of Lemma
Attacks on quantum key distribution protocols that employ non-ITS authentication
We demonstrate how adversaries with unbounded computing resources can break
Quantum Key Distribution (QKD) protocols which employ a particular message
authentication code suggested previously. This authentication code, featuring
low key consumption, is not Information-Theoretically Secure (ITS) since for
each message the eavesdropper has intercepted she is able to send a different
message from a set of messages that she can calculate by finding collisions of
a cryptographic hash function. However, when this authentication code was
introduced it was shown to prevent straightforward Man-In-The-Middle (MITM)
attacks against QKD protocols.
In this paper, we prove that the set of messages that collide with any given
message under this authentication code contains with high probability a message
that has small Hamming distance to any other given message. Based on this fact
we present extended MITM attacks against different versions of BB84 QKD
protocols using the addressed authentication code; for three protocols we
describe every single action taken by the adversary. For all protocols the
adversary can obtain complete knowledge of the key, and for most protocols her
success probability in doing so approaches unity.
Since the attacks work against all authentication methods which allow to
calculate colliding messages, the underlying building blocks of the presented
attacks expose the potential pitfalls arising as a consequence of non-ITS
authentication in QKD-postprocessing. We propose countermeasures, increasing
the eavesdroppers demand for computational power, and also prove necessary and
sufficient conditions for upgrading the discussed authentication code to the
ITS level.Comment: 34 page
Information-theoretic security under computational, bandwidth, and randomization constraints
The objective of the proposed research is to develop and analyze coding schemes for information-theoretic security, which could bridge a gap between theory an practice. We focus on two fundamental models for information-theoretic security: secret-key generation for a source model and secure communication over the wire-tap channel. Many results for these models only provide existence of codes, and few attempts have been made to design practical schemes. The schemes we would like to propose should account for practical constraints. Specifically, we formulate the following constraints to avoid oversimplifying the problems. We should assume: (1) computationally bounded legitimate users and not solely rely on proofs showing existence of code with exponential complexity in the block-length; (2) a rate-limited public communication channel for the secret-key generation model, to account for bandwidth constraints; (3) a non-uniform and rate-limited source of randomness at the encoder for the wire-tap channel model, since a perfectly uniform and rate-unlimited source of randomness might be an expensive resource. Our work focuses on developing schemes for secret-key generation and the wire-tap channel that satisfy subsets of the aforementioned constraints.Ph.D
The Security of Practical Quantum Key Distribution
Quantum key distribution (QKD) is the first quantum information task to reach
the level of mature technology, already fit for commercialization. It aims at
the creation of a secret key between authorized partners connected by a quantum
channel and a classical authenticated channel. The security of the key can in
principle be guaranteed without putting any restriction on the eavesdropper's
power.
The first two sections provide a concise up-to-date review of QKD, biased
toward the practical side. The rest of the paper presents the essential
theoretical tools that have been developed to assess the security of the main
experimental platforms (discrete variables, continuous variables and
distributed-phase-reference protocols).Comment: Identical to the published version, up to cosmetic editorial change
Reconciliation for Satellite-Based Quantum Key Distribution
This thesis reports on reconciliation schemes based on Low-Density Parity-Check (LDPC) codes in Quantum Key Distribution (QKD) protocols. It particularly focuses on a trade-off between the complexity of such reconciliation schemes and the QKD key growth, a trade-off that is critical to QKD system deployments. A key outcome of the thesis is a design of optimised schemes that maximise the QKD key growth based on finite-size keys for a range of QKD protocols. Beyond this design, the other four main contributions of the thesis are summarised as follows. First, I show that standardised short-length LDPC codes can be used for a special Discrete Variable QKD (DV-QKD) protocol and highlight the trade-off between the secret key throughput and the communication latency in space-based implementations. Second, I compare the decoding time and secret key rate performances between typical LDPC-based rate-adaptive and non-adaptive schemes for different channel conditions and show that the design of Mother codes for the rate-adaptive schemes is critical but remains an open question. Third, I demonstrate a novel design strategy that minimises the probability of the reconciliation process being the bottleneck of the overall DV-QKD system whilst achieving a target QKD rate (in bits per second) with a target ceiling on the failure probability with customised LDPC codes. Fourth, in the context of Continuous Variable QKD (CV-QKD), I construct an in-depth optimisation analysis taking both the security and the reconciliation complexity into account. The outcome of the last contribution leads to a reconciliation scheme delivering the highest secret key rate for a given processor speed which allows for the optimal solution to CV-QKD reconciliation
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