9 research outputs found
Secrecy Capacity Region of Fading Broadcast Channels
The fading broadcast channel with confidential messages (BCC) is
investigated, where a source node has common information for two receivers
(receivers 1 and 2), and has confidential information intended only for
receiver 1. The confidential information needs to be kept as secret as possible
from receiver 2. The channel state information (CSI) is assumed to be known at
both the transmitter and the receivers. The secrecy capacity region is first
established for the parallel Gaussian BCC, and the optimal source power
allocations that achieve the boundary of the secrecy capacity region are
derived. In particular, the secrecy capacity region is established for the
Gaussian case of the Csiszar-Korner BCC model. The secrecy capacity results are
then applied to give the ergodic secrecy capacity region for the fading BCC.Comment: Proc. of IEEE International Symposium on Information Theory (ISIT),
June 200
Practical LDPC coded modulation schemes for the fading broadcast channel with confidential messages
The broadcast channel with confidential messages is a well studied scenario
from the theoretical standpoint, but there is still lack of practical schemes
able to achieve some fixed level of reliability and security over such a
channel. In this paper, we consider a quasi-static fading channel in which both
public and private messages must be sent from the transmitter to the receivers,
and we aim at designing suitable coding and modulation schemes to achieve such
a target. For this purpose, we adopt the error rate as a metric, by considering
that reliability (security) is achieved when a sufficiently low (high) error
rate is experienced at the receiving side. We show that some conditions exist
on the system feasibility, and that some outage probability must be tolerated
to cope with the fading nature of the channel. The proposed solution exploits
low-density parity-check codes with unequal error protection, which are able to
guarantee two different levels of protection against noise for the public and
the private information, in conjunction with different modulation schemes for
the public and the private message bits.Comment: 6 pages, 4 figures, to be presented at IEEE ICC'14 - Workshop on
Wireless Physical Layer Securit
On the Commitment Capacity of Unfair Noisy Channels
Noisy channels are a valuable resource from a cryptographic point of view.
They can be used for exchanging secret-keys as well as realizing other
cryptographic primitives such as commitment and oblivious transfer. To be
really useful, noisy channels have to be consider in the scenario where a
cheating party has some degree of control over the channel characteristics.
Damg\r{a}rd et al. (EUROCRYPT 1999) proposed a more realistic model where such
level of control is permitted to an adversary, the so called unfair noisy
channels, and proved that they can be used to obtain commitment and oblivious
transfer protocols. Given that noisy channels are a precious resource for
cryptographic purposes, one important question is determining the optimal rate
in which they can be used. The commitment capacity has already been determined
for the cases of discrete memoryless channels and Gaussian channels. In this
work we address the problem of determining the commitment capacity of unfair
noisy channels. We compute a single-letter characterization of the commitment
capacity of unfair noisy channels. In the case where an adversary has no
control over the channel (the fair case) our capacity reduces to the well-known
capacity of a discrete memoryless binary symmetric channel
Semantically Secure Lattice Codes for Compound MIMO Channels
We consider compound multi-input multi-output (MIMO) wiretap channels where
minimal channel state information at the transmitter (CSIT) is assumed. Code
construction is given for the special case of isotropic mutual information,
which serves as a conservative strategy for general cases. Using the flatness
factor for MIMO channels, we propose lattice codes universally achieving the
secrecy capacity of compound MIMO wiretap channels up to a constant gap
(measured in nats) that is equal to the number of transmit antennas. The
proposed approach improves upon existing works on secrecy coding for MIMO
wiretap channels from an error probability perspective, and establishes
information theoretic security (in fact semantic security). We also give an
algebraic construction to reduce the code design complexity, as well as the
decoding complexity of the legitimate receiver. Thanks to the algebraic
structures of number fields and division algebras, our code construction for
compound MIMO wiretap channels can be reduced to that for Gaussian wiretap
channels, up to some additional gap to secrecy capacity.Comment: IEEE Trans. Information Theory, to appea
Physical-layer secrecy and privacy of wireless communication
The motivation of this thesis is to contribute to the improvement of the physical-layer secrecy and privacy of wireless communication. Firstly, the rate and power adaptation technique is investigated to improve the energy efficiency of the physical-layer secrecy. We present the optimum rate and power adaptation rule that maximizes the average secrecy energy efficiency(SEE) subject to an average transmission power constraint. The SEE is defined as the outage secrecy capacity, the largest secrecy rate, such that the outage probability is less than a certain value, divided by the total power consumption (bits per joule). We also characterize the SEE gain provided by varying the rate and/or the power, and discuss the impact of the number of antennas on the optimum adaptation rule. Secondly, the joint impact of imperfect knowledge of the channel gain (channel uncertainty) and noise power (noise uncertainty) at the adversary is investigated to improve the physical-layer privacy. We characterize the covert throughput gain provided by the channel uncertainty as well as the covert throughput loss caused by the channel fading as a function of the noise uncertainty. We also show the impact the channel uncertainty on the total detection error probability and the covert throughput. Our result shows that the channel fading is crucial to hiding the signal transmission, particularly when the noise uncertainty is low and/or the receive SNR is high. The impact of the channel uncertainty on the total detection error probability and the covert throughput is more significant when the noise uncertainty is larger. Finally, hiding a covert (private) message in non-orthogonal multiple access (NOMA) systems by superimposing (embedding) it under other messages is proposed.We determine the total detection error probability (sum of false alarm and missed detection probability), the adversary\u27s optimum detection strategy that minimizes the total detection error probability, and the communicator\u27s optimum message hiding strategy that maximizes the total detection error probability. Additionally, we explore exploiting the channel variations to further increase the total detection error probability. We show that the total detection error probability increases and converges to 1 as the number of users increases and that the total detection error probability, hence the covert rate, can be increased by increasing the transmission power when the channel variation is exploited
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