Study On Mixed Chaotic Sequences And Chaotic Image Encryption

With development of information technology and increasing frequency ofinformation exchange, the research on information security engineering isbecoming more and more important. As a novel technology in cryptography, digitalChaotic cipher has been attracted researcher dense interest and widely studied.Chaos, as a kind of nonlinear phenomenon, has many remarkable characteristics:such as pseudo-random, unpredictability of evolution of its orbits, properties ofmixing and sensitivity to initial conditions and system parameters. Thesecharacteristics are in accordance with the requirements of cryptography. Researchshows that there are some relations between traditional cipher and chaos.Challenges have been set with traditional cryptography because of the bulk datacapacity and high redundancy of widely-used patterns and multi-media information,while chaotic cipher has great superiority over the encryption of multi-mediainformation.This thesis introduces the development, rudimentary and relevant knowledgeof chaos theory. The preliminaries including the theory of modern cryptographyand chaos dynamics are presented at first. Then the author has discussed the chaoticsequences generated via logistic map with chaos and has claimed that this typechaotic sequences are not suitable for key stream. Based on the discussion above, aclass of mixed chaotic sequences, which are produced by combining logisticchaotic sequences and m-sequences in form of exclusive-OR, has been proposed inthis paper. The cryptographic properties, such as long period, randomicity, balance,running length, correlation function and linear complexity, of mixed chaoticsequences have been analyzed in detail. The results show that the new approachallows us to improve the complexity and the period of the chaotic system under thefinite-precision circumstances.With the superiority of chaotic cipher over imaging encryption, this thesisemphasizes on the research on chaotic imaging encryption technology and themethod of imaging permutation matrix, produced by one dimensional chaotic map,two dimensional chaotic maps respectively. This method is capable of changingoriginal images into unrecognizable chaotic images, which offers to protect the realcontent of digital images. In the application of one dimensional chaos, the author puts forward a new method of producing imaging permutation matrix by using twoone-dimensional chaotic systems, which is of high speed and good permutationeffects. In the application of two-dimensional chaos, the author puts forward andanalyzes the scheme of image fulfillment by using chaotic system, which is basedon the analysis of characteristic of Baker mapping in imaging encryption.Finally, the summarization has been obtained and the future researchdirections have been also given.