20 research outputs found
The Wiretap Channel with Feedback: Encryption over the Channel
In this work, the critical role of noisy feedback in enhancing the secrecy
capacity of the wiretap channel is established. Unlike previous works, where a
noiseless public discussion channel is used for feedback, the feed-forward and
feedback signals share the same noisy channel in the present model. Quite
interestingly, this noisy feedback model is shown to be more advantageous in
the current setting. More specifically, the discrete memoryless modulo-additive
channel with a full-duplex destination node is considered first, and it is
shown that the judicious use of feedback increases the perfect secrecy capacity
to the capacity of the source-destination channel in the absence of the
wiretapper. In the achievability scheme, the feedback signal corresponds to a
private key, known only to the destination. In the half-duplex scheme, a novel
feedback technique that always achieves a positive perfect secrecy rate (even
when the source-wiretapper channel is less noisy than the source-destination
channel) is proposed. These results hinge on the modulo-additive property of
the channel, which is exploited by the destination to perform encryption over
the channel without revealing its key to the source. Finally, this scheme is
extended to the continuous real valued modulo- channel where it is
shown that the perfect secrecy capacity with feedback is also equal to the
capacity in the absence of the wiretapper.Comment: Submitted to IEEE Transactions on Information Theor
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
On Secrecy Metrics for Physical Layer Security over Quasi-Static Fading Channels
Theoretical studies on physical layer security often adopt the secrecy outage
probability as the performance metric for wireless communications over
quasi-static fading channels. The secrecy outage probability has two
limitations from a practical point of view: a) it does not give any insight
into the eavesdropper's decodability of confidential messages; b) it cannot
characterize the amount of information leakage to the eavesdropper when an
outage occurs. Motivated by the limitations of the secrecy outage probability,
we propose three new secrecy metrics for secure transmissions over quasi-static
fading channels. The first metric establishes a link between the concept of
secrecy outage and the decodability of messages at the eavesdropper. The second
metric provides an error-probability-based secrecy metric which is typically
used for the practical implementation of secure wireless systems. The third
metric characterizes how much or how fast the confidential information is
leaked to the eavesdropper. We show that the proposed secrecy metrics
collectively give a more comprehensive understanding of physical layer security
over fading channels and enable one to appropriately design secure
communication systems with different views on how secrecy is measured.ARC Discovery Projects Grant DP15010390
Low-resolution ADC receiver design, MIMO interference cancellation prototyping, and PHY secrecy analysis.
This dissertation studies three independent research topics in the general field of wireless communications. The first topic focuses on new receiver design with low-resolution analog-to-digital converters (ADC). In future massive multiple-input-multiple-output (MIMO) systems, multiple high-speed high-resolution ADCs will become a bottleneck for practical applications because of the hardware complexity and power consumption. One solution to this problem is to adopt low-cost low-precision ADCs instead. In Chapter II, MU-MIMO-OFDM systems only equipped with low-precision ADCs are considered. A new turbo receiver structure is proposed to improve the overall system performance. Meanwhile, ultra-low-cost communication devices can enable massive deployment of disposable wireless relays. In Chapter III, the feasibility of using a one-bit relay cluster to help a power-constrained transmitter for distant communication is investigated. Nonlinear estimators are applied to enable effective decoding. The second topic focuses prototyping and verification of a LTE and WiFi co-existence system, where the operation of LTE in unlicensed spectrum (LTE-U) is discussed. LTE-U extends the benefits of LTE and LTE Advanced to unlicensed spectrum, enabling mobile operators to offload data traffic onto unlicensed frequencies more efficiently and effectively. With LTE-U, operators can offer consumers a more robust and seamless mobile broadband experience with better coverage and higher download speeds. As the coexistence leads to considerable performance instability of both LTE and WiFi transmissions, the LTE and WiFi receivers with MIMO interference canceller are designed and prototyped to support the coexistence in Chapter IV. The third topic focuses on theoretical analysis of physical-layer secrecy with finite blocklength. Unlike upper layer security approaches, the physical-layer communication security can guarantee information-theoretic secrecy. Current studies on the physical-layer secrecy are all based on infinite blocklength. Nevertheless, these asymptotic studies are unrealistic and the finite blocklength effect is crucial for practical secrecy communication. In Chapter V, a practical analysis of secure lattice codes is provided
Coding and Signal Processing for Secure Wireless Communication
Wireless communication networks are widely deployed today and the networks are used in many applications which require that the data transmitted be secure. Due to the open nature of wireless systems, it is important to have a fundamental understanding of coding schemes that allow for simultaneously secure and reliable transmission. The information theoretic approach is able to give us this fundamental insight into the nature of the coding schemes required for security. The security issue is approached by focusing on the confidentiality of message transmission and reception at the physical layer. The goal is to design coding and signal processing schemes that provide security, in the information theoretic sense. In so doing, we are able to prove the simultaneously secure and reliable transmission rates for different network building blocks. The multi-receiver broadcast channel is an important network building block, where the rate region for the channel without security constraints is still unknown. In the thesis this channel is investigated with security constraints, and the secure and reliable rates are derived for the proposed coding scheme using a random coding argument. Cooperative relaying is next applied to the wiretap channel, the fundamental physical layer model for the communication security problem, and signal processing techniques are used to show that the secure rate can be improved in situations where the secure rate was small due to the eavesdropper enjoying a more favorable channel condition compared to the legitimate receiver. Finally, structured lattice codes are used in the wiretap channel instead of unstructured random codes, used in the vast majority of the work so far. We show that lattice coding and decoding can achieve the secrecy rate of the Gaussian wiretap channel; this is an important step towards realizing practical, explicit codes for the wiretap channel
D11.2 Consolidated results on the performance limits of wireless communications
Deliverable D11.2 del projecte europeu NEWCOM#The report presents the Intermediate Results of N# JRAs on Performance Limits of Wireless Communications and highlights the fundamental issues that have been investigated by the WP1.1. The report illustrates the Joint Research Activities (JRAs) already identified during the first year of the project which are currently ongoing. For each activity there is a description, an illustration of the adherence and relevance with the identified fundamental open issues, a short presentation of the preliminary results, and a roadmap for the joint research work in the next year. Appendices for each JRA give technical details on the scientific activity in each JRA.Peer ReviewedPreprin
Physical-Layer Security in Wireless Communication Systems
The use of wireless networks has grown significantly in contemporary
times, and continues to develop further. The broadcast nature of
wireless communications, however, makes them particularly vulnerable
to eavesdropping. Unlike traditional solutions, which usually handle
security at the application layer, the primary concern of this
dissertation is to analyze and develop solutions based on coding
techniques at the physical-layer.
First, in chapter , we consider a scenario where a source node
wishes to broadcast two confidential messages to two receivers,
while a wire-tapper also receives the transmitted signal. This model
is motivated by wireless communications, where individual secure
messages are broadcast over open media and can be received by any
illegitimate receiver. The secrecy level is measured by the
equivocation rate at the eavesdropper. We first study the general
(non-degraded) broadcast channel with an eavesdropper, and present
an inner bound on the secrecy capacity region for this model. This
inner bound is based on a combination of random binning, and the
Gelfand-Pinsker binning. We further study the situation in which the
channels are degraded. For the degraded broadcast channel with an
eavesdropper, we present the secrecy capacity region. Our achievable
coding scheme is based on Cover's superposition scheme and random
binning. We refer to this scheme as the Secret Superposition Scheme.
Our converse proof is based on a combination of the converse proof
of the conventional degraded broadcast channel and Csiszar Lemma. We
then assume that the channels are Additive White Gaussian Noise and
show that the Secret Superposition Scheme with Gaussian codebook is
optimal. The converse proof is based on Costa's entropy power
inequality. Finally, we use a broadcast strategy for the slowly
fading wire-tap channel when only the eavesdropper's channel is
fixed and known at the transmitter. We derive the optimum power
allocation for the coding layers, which maximizes the total average
rate.
Second, in chapter , we consider the
Multiple-Input-Multiple-Output (MIMO) scenario of a broadcast
channel where a wiretapper also receives the transmitted signal via
another MIMO channel. First, we assume that the channels are
degraded and the wiretapper has the worst channel. We establish the
capacity region of this scenario. Our achievability scheme is the
Secret Superposition Coding. For the outerbound, we use notion of
the enhanced channels to show that the secret superposition of
Gaussian codes is optimal. We show that we only need to enhance the
channels of the legitimate receivers, and the channel of the
eavesdropper remains unchanged. We then extend the result of the
degraded case to a non-degraded case. We show that the secret
superposition of Gaussian codes, along with successive decoding,
cannot work when the channels are not degraded. We develop a Secret
Dirty Paper Coding scheme and show that it is optimal for this
channel. We then present a corollary generalizing the capacity
region of the two receivers case to the case of multiple receivers.
Finally, we investigate a scenario which frequently occurs in the
practice of wireless networks. In this scenario, the transmitter and
the eavesdropper have multiple antennae, while both intended
receivers have a single antenna (representing resource limited
mobile units). We characterize the secrecy capacity region in terms
of generalized eigenvalues of the receivers' channels and the
eavesdropper's channel. We refer to this configuration as the MISOME
case. We then present a corollary generalizing the results of the
two receivers case to multiple receivers. In the high SNR regime, we
show that the capacity region is a convex closure of rectangular
regions.
Finally, in chapter , we consider a -user secure Gaussian
Multiple-Access-Channel with an external eavesdropper. We establish
an achievable rate region for the secure discrete memoryless MAC.
Thereafter, we prove the secrecy sum capacity of the degraded
Gaussian MIMO MAC using Gaussian codebooks. For the non-degraded
Gaussian MIMO MAC, we propose an algorithm inspired by the
interference alignment technique to achieve the largest possible
total Secure-Degrees-of-Freedom . When all the terminals are
equipped with a single antenna, Gaussian codebooks have shown to be
inefficient in providing a positive S-DoF. Instead, we propose a
novel secure coding scheme to achieve a positive S-DoF in the single
antenna MAC. This scheme converts the single-antenna system into a
multiple-dimension system with fractional dimensions. The
achievability scheme is based on the alignment of signals into a
small sub-space at the eavesdropper, and the simultaneous separation
of the signals at the intended receiver. We use tools from the field
of Diophantine Approximation in number theory to analyze the
probability of error in the coding scheme. We prove that the total
S-DoF of can be achieved for almost all channel
gains. For the other channel gains, we propose a multi-layer coding
scheme to achieve a positive S-DoF. As a function of channel gains,
therefore, the achievable S-DoF is discontinued