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Abstract A long with the rapid development of Internet and universal application of multimedia technology, more and more information including audio, image, and other multimedia, has been transmitted over unsecured channels. In particular, image security has attracted more and more attention since images have been widely used in daily life. For example, people use images including military photographs, and financial records etc., to exchange all kinds of information. Yet the main obstacle in the widespread deployment of digital multimedia services has been enforcing security and ensuring authorized access to sensitive data. A direct solution is to use an encryption algorithm to mask the multimedia data streams. In this regard, traditional encryption algorithms that based on celebrated number theory, algebra, and computer arithmetic such as IDEA, AES, DES, RSA etc. could be used. However, these encryption schemes have been invented to text encryption and appear not to be ideal for image applications due to some intrinsic features of images such as bulk data capacity, high correlation between pixels and high redundancy, which are troublesome for traditional encryption. Moreover, these encryption schemes require extra operations on compressed image data, thereby demanding long computational time and high computing power. In real time communication, because of their low encryption and decryption speeds, they may introduce significant latency. In order to develop effective image encryption techniques, these have to be fully understood. Recently, some researchers have pointed out that there exists tight relationship between cellular automata (CA) and v cryptography. Many features of cellular automata, such as the periodicity, mixing and the sensitivity to initial conditions, can be connected with the “confusion” and “diffusion” property in cryptography. An elementary cellular automaton (ECA) is the simplest class of one-dimensional cellular automata, which is a linear array of cells with three neighborhood dependency, and state of each cell is 0 or 1. Based on ECA, there are a number of image encryption schemes have been proposed in the literature. However, due to the lack of a strict scrutiny on the security, some of them have been found insecure against various attacks. This dissertation studies the security problems of some image encryption schemes based on cellular automata to known the strength and weakness in their design. In addition, we propose a new self adaptive image encryption scheme based on 2D reversible memory cellular automata. Research Objectives This dissertation involves the following aspects about cellular automata (CA) and cellular neural network ciphers (CNN): cryptanalysis of the recently-proposed ciphers based on cellular automata and designs a new image encryption that overcomes the weakness of the previous schemes. vi The main contribution of this dissertation can be summarized as follows: 1. Analyze the scheme based on elementary cellular automata (ECA) proposed in [72] .Based on the given analysis, it is demonstrated that the scheme under study can be broken by several attacks. Similarly, analyze the image encryption based on elementary cellular automata proposed in [77] Based on the given analysis, we report the following problems: a) the scheme is not sensitive with respect to both the changes of plain-images and key streams generated by ECA; b) the scheme can be broken by various cryptanalysis. (The above contribution has been published in the journal of Advanced Materials Research) 2. It’s demonstrated that the scheme of [95], the scheme for Image Encryption based on Cellular Automata and Arnold Cat’s map, is not secure against the following attacks: known plaintext and chosen plaintext. In addition the scheme is insensitive to the change of the secret plain-image. 3. Design Self-Adaptive Image Encryption Based on 2D Reversible Memory Cellular Automata. We propose a novel secret image encryption scheme based on two dimensional cellular automata with reversible transition function. The thesis organized into four chapters as follows: Chapter one gives an overview of cryptography, cellular automata and cellular neural network. vii Chapter two gives the proposed cryptanalysis of the main recently schemes based on elementary cellular automata [72, 77, 95]. Chapter three gives the proposed image encryption scheme based on 2D reversible memory cellular automata and cellular neural network. Chapter four gives the conclusion and future works. viii TABLE OF |