67 research outputs found
Construction of Codes for Wiretap Channel and Secret Key Agreement from Correlated Source Outputs by Using Sparse Matrices
The aim of this paper is to prove coding theorems for the wiretap channel
coding problem and secret key agreement problem based on the the notion of a
hash property for an ensemble of functions. These theorems imply that codes
using sparse matrices can achieve the optimal rate. Furthermore, fixed-rate
universal coding theorems for a wiretap channel and a secret key agreement are
also proved.Comment: A part of this paper is presented in part at 2009 IEEE Information
Theory Workshop (ITW2009), Taormina, Italy, pp.105-109, 2009. This paper is
submitted to IEEE Transactions on Information Theory. 34 page
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
Message Authentication Code over a Wiretap Channel
Message Authentication Code (MAC) is a keyed function such that when
Alice, who shares the secret with Bob, sends to the latter, Bob
will be assured of the integrity and authenticity of . Traditionally, it is
assumed that the channel is noiseless. However, Maurer showed that in this case
an attacker can succeed with probability after
authenticating messages. In this paper, we consider the setting where
the channel is noisy. Specifically, Alice and Bob are connected by a discrete
memoryless channel (DMC) and a noiseless but insecure channel. In
addition, an attacker Oscar is connected with Alice through DMC and with
Bob through a noiseless channel. In this setting, we study the framework that
sends over the noiseless channel and the traditional MAC over
channel . We regard the noisy channel as an expensive resource and
define the authentication rate as the ratio of message length to
the number of channel uses. The security of this framework depends on
the channel coding scheme for . A natural coding scheme is to use the
secrecy capacity achieving code of Csisz\'{a}r and K\"{o}rner. Intuitively,
this is also the optimal strategy. However, we propose a coding scheme that
achieves a higher Our crucial point for this is that in the
secrecy capacity setting, Bob needs to recover while in our coding
scheme this is not necessary. How to detect the attack without recovering
is the main contribution of this work. We achieve this through random
coding techniques.Comment: Formulation of model is change
Achievable secrecy enchancement through joint encryption and privacy amplification
In this dissertation we try to achieve secrecy enhancement in communications by resorting to both cryptographic and information theoretic secrecy tools and metrics. Our objective is to unify tools and measures from cryptography community with techniques and metrics from information theory community that are utilized to provide privacy and confidentiality in communication systems. For this purpose we adopt encryption techniques accompanied with privacy amplification tools in order to achieve secrecy goals that are determined based on information theoretic and cryptographic metrics. Every secrecy scheme relies on a certain advantage for legitimate users over adversaries viewed as an asymmetry in the system to deliver the required security for data transmission. In all of the proposed schemes in this dissertation, we resort to either inherently existing asymmetry in the system or proactively created advantage for legitimate users over a passive eavesdropper to further enhance secrecy of the communications. This advantage is manipulated by means of privacy amplification and encryption tools to achieve secrecy goals for the system evaluated based on information theoretic and cryptographic metrics. In our first work discussed in Chapter 2 and the third work explained in Chapter 4, we rely on a proactively established advantage for legitimate users based on eavesdropper’s lack of knowledge about a shared source of data. Unlike these works that assume an errorfree physical channel, in the second work discussed in Chapter 3 correlated erasure wiretap channel model is considered. This work relies on a passive and internally existing advantage for legitimate users that is built upon statistical and partial independence of eavesdropper’s channel errors from the errors in the main channel. We arrive at this secrecy advantage for legitimate users by exploitation of an authenticated but insecure feedback channel. From the perspective of the utilized tools, the first work discussed in Chapter 2 considers a specific scenario where secrecy enhancement of a particular block cipher called Data Encryption standard (DES) operating in cipher feedback mode (CFB) is studied. This secrecy enhancement is achieved by means of deliberate noise injection and wiretap channel encoding as a technique for privacy amplification against a resource constrained eavesdropper. Compared to the first work, the third work considers a more general framework in terms of both metrics and secrecy tools. This work studies secrecy enhancement of a general cipher based on universal hashing as a privacy amplification technique against an unbounded adversary. In this work, we have achieved the goal of exponential secrecy where information leakage to adversary, that is assessed in terms of mutual information as an information theoretic measure and Eve’s distinguishability as a cryptographic metric, decays at an exponential rate. In the second work generally encrypted data frames are transmitted through Automatic Repeat reQuest (ARQ) protocol to generate a common random source between legitimate users that later on is transformed into information theoretically secure keys for encryption by means of privacy amplification based on universal hashing. Towards the end, future works as an extension of the accomplished research in this dissertation are outlined. Proofs of major theorems and lemmas are presented in the Appendix
Finite-Block-Length Analysis in Classical and Quantum Information Theory
Coding technology is used in several information processing tasks. In
particular, when noise during transmission disturbs communications, coding
technology is employed to protect the information. However, there are two types
of coding technology: coding in classical information theory and coding in
quantum information theory. Although the physical media used to transmit
information ultimately obey quantum mechanics, we need to choose the type of
coding depending on the kind of information device, classical or quantum, that
is being used. In both branches of information theory, there are many elegant
theoretical results under the ideal assumption that an infinitely large system
is available. In a realistic situation, we need to account for finite size
effects. The present paper reviews finite size effects in classical and quantum
information theory with respect to various topics, including applied aspects
A Critical Review of Physical Layer Security in Wireless Networking
Wireless networking has kept evolving with additional features and increasing capacity. Meanwhile, inherent characteristics of wireless networking make it more vulnerable than wired networks. In this thesis we present an extensive and comprehensive review of physical layer security in wireless networking. Different from cryptography, physical layer security, emerging from the information theoretic assessment of secrecy, could leverage the properties of wireless channel for security purpose, by either enabling secret communication without the need of keys, or facilitating the key agreement process. Hence we categorize existing literature into two main branches, namely keyless security and key-based security. We elaborate the evolution of this area from the early theoretic works on the wiretap channel, to its generalizations to more complicated scenarios including multiple-user, multiple-access and multiple-antenna systems, and introduce not only theoretical results but practical implementations. We critically and systematically examine the existing knowledge by analyzing the fundamental mechanics for each approach. Hence we are able to highlight advantages and limitations of proposed techniques, as well their interrelations, and bring insights into future developments of this area
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