The Researches Of Multimedia Information Security Algorithms Based On Chaotic Theory

With the development of computer technology and network communication, the protection of multimedia content in the context of information security has attracted more and more attentions in recent years. Due to the intrinsic properties of multimedia such as high redundancy and bulk capacity, peculiar attention should be paid to operation speed, self-authentication and noninterference of the availability of data, etc. The validity of multimedia protection can not be met by traditional cryptology due to the issues mentioned above.In consideration of the disadvantage of traditional cryptology, more effective approaches were studied and investigated to meet the requirement of multimedia protection, among which chaos based encryption and digital watermarking technology exhibit prospective advantage.In this dissertation, some issues on multimedia protection are studied and several discrete chaos based encryption schemes and multimedia watermarking algorithms are investigated as well, which are detailed as follows:(1) In the context of chaos theory research, the chaotic dynamical degeneration phenomena caused by the periodicity and finite precision of discrete chaotic system are studied firstly. The"wide"existence of the invalid-keys and the quasi invalid-keys are analysed by means of the existence periodic points in one dimensional chaotic dynamical system. Then five improved schemes of discrete chaotic key stream generation, which include binary chaotic pseudo-random, N-bit sequences and two-dimension chaotic matrix, are proposed based on the research above. Researches on the group properties in discrete chaotic system are the most significant part in this dissertation, from which it can be concluded that fixed chaos bit or integer sequences are XOR groups, and chaos permutation sequences and two-dimension permutation matrix are permutation groups. As the conclusion indicates, it can be guided to support the design of various encryption algorithms based on'permuting'and'mixing'.(2) Concerning the digital image encryption, an improved algorithm of chaotic block cipher for image encryption combined with'permutation','substitution'and'mixing'is proposed to resist the plain text attack, statistic analysis and difference attack. Then an improved encrypt scheme based on two-dimensiones Arnold map and chaos permutation matrix is proposed on the researches of periodical phenomena on the two-dimensiones discrete Arnold map. A color image encryption scheme based on three-dimensiones Arnold map in DCT field is proposed by means of extending the dimension from two to three. The significant performance improvement is proved by cryptanalysis and experiments.(3) In the context of encryption schemes based on chaotic stream cipher, taking MPEG-2 video stream as main encryption objects, several improved algorithms and encryption schemes for compressed video stream are proposed to provide direct and fast encryption operation. The proposed entire-encryption algorithms utilize the outstanding randomicity and key sensitivity of chaotic stream cipher to provide high level security and enhance the algorithm operation speed simultaneous. Then a scheme candidate of designing S-box based on discrete chaotic system is introduced to process the substitution for improving the ability of resisting difference attack and linear attack.(4) Concerning with digital watermarking based on chaotic dynamical system, two algorithms are proposed by utilizing the advantages of chaotic sequence, which include the initial value's sensitivity, randomicity, ergodicity and the bulkiness of key space. The proposed"half-fragile"digital watermarking algorithm can support detection and orientation of the modification, while the proposed multifunctional digital watermarking algorithm can provide various watermarking functions such as integrity authentication and copyright authentication. The application method of chaos system on digital watermarking has been expanded at the same time.Finally, the thesis is concluded by pointing out some open issues on the current research of chaos based encryption and digital watermarking as well as indicating further research directions.