published_or_final_version / Electrical and Electronic Engineering / Doctoral / Doctor of Philosophy

M. Tech. Electrical Engineering. / This dissertation presents encryption and decryption of digital message signal and image data based on Qi hyper chaos system. The field of telecommunication has grown rapidly especially with the introduction of mobile phone and internet networks. Associated with this growth, there is a vital need to have a secure communication of information.

M. Tech. Electrical engineering. / Discusses a desirable chaos-based encryption scheme for image storage and transmission is one that can resist different types of attacks in less time and with successful decryption. To resist different kinds of attacks, a higher security level is required. As a result, there is a need to enhance the security level of existing chaos-based image encryption schemes using hyper-chaos. To increase the level of security using hyper-chaos, the research will present a scheme that combines two different techniques that are used to improve the degree of security of chaos-based cryptography; a classical chaos-based cryptographic technique and a hyper-chaos masking technique. The first technique focuses on the efficient combination and transformation of image characteristics based on hyper-chaos pseudorandom numbers. The second technique focuses on driving the hyper-chaos system by using the results of the first technique to change the transmitted chaos dynamic as well as using synchronisation and a high-order differentiator for decryption. To achieve the objective of our research the following sub-problems are addressed.

The Organization for Economic Co-operation and Development (OECD) issued on 27 March 1997 a recommendation concerning cryptography policy guidelines in an attempt to foster international co-operation and harmonization. Information is becoming increasingly valuable in society. Globalization of markets, improvements in information and communication technology and the shift to a knowledge-based economy has, furthermore, created an enormous potential for electronic commerce. Conservative estimates predict electronic commerce will have a turnover of more than US $400 billion by 2002. The increasing importance of information and communications has, however, made the information society vulnerable. Cryptography plays an important part in securing transactions in electronic commerce and moreover, in establishing a secure electronic environment in the information society. Fear of privacy infringements and lack of secure methods for electronic transactions has until now been holding electronic commerce back. Cryptographic methods are an essential part in securing electronic commerce. Law enforcement agencies and national security organizations fear, however, that widespread use of strong encryption will impede their work substantially. This thesis analyzes the advantages and disadvantages of strong encryption and how the balance of the conflicting interests has been dealt with in the OECD Cryptography Policy Guidelines. Moreover, shows the thesis how the OECD Cryptography Policy Guidelines have been implemented and makes suggestions on how the guidelines should be implemented.

Digital image steganography has been made relevant by the rapid increase in media sharing over the Internet and has thus experienced a renaissance. This dissertation starts with a discussion of the role of modern digital image steganography and cell-based digital image stego-systems which are the focus of this work. Of particular interest is the fact that cell-based stego-systems have good security properties but relatively poor embedding capacity. The main research problem is stated as the development of an approach to improve embedding capacity in cell-based systems. The dissertation then tracks the development of digital image stego-systems from spatial and naïve to transform-based and complex, providing the context within which cell-based systems have emerged and re-states the research problem more specifically as the development of an approach to determine more efficient data embedding and error coding schemes in cell-based stego-systems to improve embedding capacity while maintaining security. The dissertation goes on to describe the traditional application of data handling procedures particularly relating to the likely eventuality of JPEG compression of the image containing the hidden information (i.e. stego-image) and proposes a new approach. The approach involves defining a different channel model, empirically determining channel characteristics and using them in conjunction with error coding systems and security selection criteria to find data handling parameters that optimise embedding capacity in each channel. Using these techniques and some reasoning regarding likely cover image size and content, image-global error coding is also determined in order to keep the image error rate below 1% while maximising embedding capacity. The performance of these new data handling schemes is tested within cell-based systems. Security of these systems is shown to be maintained with an up to 7 times improvement in embedding capacity. Additionally, up to 10% of embedding capacity can be achieved versus simple LSB embedding. The 1% image error rate is also confirmed to be upheld. The dissertation ends with a summary of the major points in each chapter and some suggestions of future work stemming from this research. / Thesis (M.Sc.Eng.)-University of KwaZulu-Natal, Durban, 2012.

Wireless networks afford many benefits compared to wired networks in terms of their usability in dynamic situations, mobility of networked devices, and accessibility of hazardous environments. The devices used in these networks are generally assumed to be limited in resources such as energy, memory, communications range, and computational ability. Operating in remote or hostile environments, this places them in danger of being compromised by some malicious entity. This work addresses these issues to increase the security of these networks while still maintaining acceptable levels of networking performance and resource usage. We investigate new methods for data encryption on personal wireless hand-held devices. An important consideration for resource-constrained devices is the processing required to encrypt data for transmission or for secure storage. Significant latency from data encryption diminishes the viability of these security services for hand-held devices. Also, increased processing demands require additional energy for each device, where both energy and processing capability are limited. Therefore, one area of interest for hand-held wireless devices is being able to provide data encryption while minimizing the processing and energy overhead as a cost to provide such a security service. We study the security of a wavelet-based cryptosystem and consider its viability for use in hand-held devices. This thesis also considers the performance of wireless sensor networks in the presence of an adversary. The sensor nodes used in these networks are limited in available energy, processing capability and transmission range. Despite these resource constraints and expected malicious attacks on the network, these networks require widespread, highly-reliable communications. Maintaining satisfactory levels of network performance and security between entities is an important goal toward ensuring the successful and accurate completion of desired sensing tasks. However, the resource-constrained nature of the sensor nodes used in these applications provides challenges in meeting these networking and security requirements. We consider link-compromise attacks and node-spoofing attacks on wireless sensor networks, and we consider the performance of various key predistribution schemes applied to these networks. New key predistribution techniques to improve the security of wireless sensor networks are proposed.

In the age of information explosion, there is huge amount of information generated every second. Some of the information generated, for example news, is supposed to be shared by public and anyone in the world can get a copy of it. However, sometimes, information is only supposed to be maintain private or only shared by a given group of people. In the latter case, information protection becomes very important. There are various ways to protect information. One of the technical ways is cryptography, which is an area of interest for mathematicians, computer scientists and physicists. As a new area in cryptography, physical layer security has been paid great attention recently. Quantum key distribution is a hot research topic for physical layer security in the two decades. This thesis focuses on two quantum key distribution protocols that can potentially increase the key generation rate and lower the cost. On protocol is based on amplified spontaneous emission as signal source and the other one is based on discretely signaled continuous variable quantum communication. The security analysis and experimental implementation issues for both protocols are discussed.

Kerberos is a widely-deployed network authentication protocol that is being considered for standardization. Like other standard protocols, Kerberos is no exception to security flaws and weaknesses, as has been demonstrated in several prior works. Provable security guarantees go a long way in restoring users' faith, thus making a protocol an even stronger candidate for standards. In this thesis, our goal was thus to provide provable security support for Kerberos and other practical protocols. Our contributions are three-fold: We first look at the symmetric encryption schemes employed in the current version 5 of Kerberos. Several recent results have analyzed a significant part of Kerberos v.5 using formal-methods-based approaches, which are meaningful only if the underlying encryption schemes satisfy strong cryptographic notions of privacy and authenticity. However, to our knowledge these schemes were never analyzed and proven to satisfy such notions. This thesis aims to bridge this gap. Our provable security analyses confirm that some of the encryption scheme options in Kerberos v.5 already provide privacy and authenticity, and for the remaining we suggest slight modifications for the same. We next turn our attention to the ways in which the keys and other random strings needed in cryptographic schemes employed by practical protocols are generated. Randomness needs to be carefully generated for the provable security guarantees to hold. We propose an efficient pseudorandom generator (PRG) based on hash functions. The security of our PRG relies on exponential collision-resistance and regularity of the underlying hash function. Our PRG can be used to generate various strings, like session keys, sequence numbers, confounders, etc., which are all suggested to be generated randomly in the Kerberos v.5 specification, but no algorithms are mentioned. Each of the above strings are required to satisfy different properties, all of which are trivially satisfied by the pseudorandom strings output by a PRG. Finally, we look at the problem of revocation associated with two relatively new types of encryption schemes: identity-based encryption (IBE) and attribute-based encryption (ABE). While these encryption schemes are relatively less efficient compared to public-key encryption schemes, they have already been used (and are very likely to be used in future, as well) in many practical protocols due to their attractive features. Any setting, public-key, identity-based, or attribute-based, must provide a means to revoke users from the system. However, unlike public-key encryption, there has been little prior work on studying the revocation mechanisms in an IBE or ABE. We propose new primitives and their efficient and provably secure instantiations, focusing on the revocation problem. We would like to note that even though all the results presented in this thesis are motivated mainly by provable security in practice, only the first bullet above has a direct impact on a practical and widely deployed protocol Kerberos. Our PRG is the most efficient construction among theoretical PRGs, but it may still not be efficient enough to be directly usable in practical protocols. And our results and techniques for revocation in IBE and ABE have found much wider applications in information security, such as mobile social networks, cloud-based secure health records, data outsourcing systems, vehicular ad-hoc networks, etc.

Thesis (M.S.)--University of North Texas, Aug., 2007. / Title from title page display. Includes bibliographical references.

Thesis (Ph. D.)--School Computing and Engineering. University of Missouri--Kansas City, 2006. / "A dissertation in computer networking and software architecture." Advisor: Lein Harn. Typescript. Vita. Title from "catalog record" of the print edition Description based on contents viewed Nov. 13, 2007. Includes bibliographical references (leaves 203-214). Online version of the print edition.