28-08-2013, 03:49 PM
Wireless Information-Theoretic Security
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Abstract
This paper considers the transmission of confidential
data over wireless channels. Based on an information-theoretic for-
mulation of the problem, in which two legitimates partners com-
municate over a quasi-static fading channel and an eavesdropper
observes their transmissions through a second independent quasi-
static fading channel, the important role of fading is character-
ized in terms of average secure communication rates and outage
probability. Based on the insights from this analysis, a practical
secure communication protocol is developed, which uses a four-
step procedure to ensure wireless information-theoretic security:
(i) common randomness via opportunistic transmission, (ii) mes-
sage reconciliation, (iii) common key generation via privacy am-
plification, and (iv) message protection with a secret key. A rec-
onciliation procedure based on multilevel coding and optimized
low-density parity-check (LDPC) codes is introduced, which allows
to achieve communication rates close to the fundamental security
limits in several relevant instances. Finally, a set of metrics for as-
sessing average secure key generation rates is established, and it is
shown that the protocol is effective in secure key renewal—even in
the presence of imperfect channel state information.
INTRODUCTION
Motivation
HE issues of privacy and security in wireless communica-
tion networks have taken on an increasingly important role
as these networks continue to flourish worldwide. Traditionally,
security is viewed as an independent feature addressed above
the physical layer, and all widely used cryptographic protocols
(e.g., RSA and AES) are designed and implemented assuming
the physical layer has already been established and provides an
error-free link. In contrast with this paradigm, there exist both
theoretical and practical contributions that support the poten-
tial of physical layer security ideas to significantly strengthen
the security of digital communication systems. The basic prin-
ciple of information-theoretic security
LDPC Code Construction for Gaussian Reconciliation
In this subsection, we develop an efficient reconciliation ap-
proach for the second step of the key agreement protocol. The
reconciliation of binary random variables has been extensively
studied and several efficient methods have been proposed [37],
however, little attention has been devoted to the practical rec-
onciliation of nonbinary random variables [26].
Performance Metrics for Secure Communications
The information-theoretically secure rates of the secret key
agreement protocol can be assessed only if the keys are used in
conjunction with a one-time pad. However, in principle, the pro-
tocol could also be tailored to standard encryption algorithms
offering computational complexity. Although no information-
theoretic security can be guaranteed in this latter case, com-
bining a physical-layer key-generation technique with a sym-
metric encryption scheme can still be a valid way of enhancing
security. In fact, key-generation rates can be substantially higher
than those offered by public-key schemes; moreover, keys gen-
erated from the physical layer are independent from one another,
which ensures that the security of the system is re-initialized at
each round of key-generation. An attacker who gains access to
one key would be none the wiser once the key is renewed. Based
on these considerations, we evaluate the performance of the op-
portunistic protocol using the following metric.
CONCLUSION
Concluding Remarks
We proposed a protocol based on one-way communications
providing secure communication over quasi-static wireless
channels. This scheme opportunistically exploits the fluctua-
tions of the fading coefficients to generate information-theo-
retically secure keys, which are then used to encrypt messages
prior to transmission. We analyzed the security provided by the
protocol in the idealized case where channel state information
about the wiretap channel is available, but also showed that
secure communication is still achievable in the more realistic
situation where only imperfect channel state information can
be obtained.