Research On Chaos Based Image Encryption And Watermarking Technology

The advance of digital signal processing and the prevalence of network communication make the protection of multimedia content become a crucial issue in information security that attracted much attention of both the government and the public. Due to the intrinsic properties of multimedia such as high redundancy and bulk capacity, special concerns have to be made, which includes speediness of operation, low computational overload, self-authentication of the data and noninterference of the availability of data. All these matters have risen up a great puzzle in multimedia protection, which current cryptology feels difficult to deal with.In consideration of the deficiency of traditional cryptology, recently people are seeking more effective approaches to fulfill the requirements of multimedia protection, among which chaos based encryption and digital watermarking technology exhibit prospective superiority.In this dissertation, some issues in image security are studied and several chaos based encryption schemes and image watermarking algorithms are composed as well, which are detailed as follows:(1) Relationship between cryptological transformation and chaotic map is investigated in terms of chaotic properties and methodology on design of chaotic block cipher for image encryption is provided. Concerning with image encryption, several encryption schemes based on high dimensional reversible chaotic map are put forth such as one based on cat map or Baker map. To fasten operation speed and enhance encryption security, a novel image encryption scheme based on three dimensional Baker map that extended from its two dimensional counterpart is brought out. The significant performance improvement is proved by cryptanalysis and experiments.(2) Universal approaches to generating chaotic pseudo-random sequence, especially to chaotic pseudo-random bit sequence (CPRBS), are studied and two CPRBS generation algorithms are investigated in detail. Properties of the CPRBS generated by one of the two algorithms are further explored. Then, to solve the degradationcaused by digitization that unavoidable in practical realization, a chaotic stream cipher taking use of chaotic feedback shift registers is brought out, which has been shaped to be implemented in digital chip. Finally an image encryption method jointly using SPIHT wavelet compression and chaos is proposed. The dual merits that either being able to perform encryption on compressed data stream or not losing the progressive data transmission property that inherently possessed by original SPIHT coding makes the method a promising encryption scheme for practical use.(3) To meet the requirement of invisibility of image watermarking, human visual properties have been investigated in the thesis. Three kinds of robust perceptual watermarking techniques that take use of Discrete Gaussion Transform (DGT), Discrete Wavelet Transform (DWT) accompanied with image fusion and Discrete Cosine Transform (DCT) combined with visual contrast sensitivity function respectively also have been proposed. Empirical study shows that HVS based watermarking schemes can significantly increase the robustness of watermark while reduce image quality degradation.(4) As chaos based watermarking has emerged as a new research direction, efforts on composition of chaotic watermark have also been made by putting forward a semi-fragile watermarking scheme that incorporated with two dimensional Baker map for authentication purpose. The algorithm can not only judge image tamper but also find out the tamper location in image even in face of noise addition and mild JPEG compression.Finally, the thesis is concluded by pointing out some open issues on the research of chaos based encryption and image watermarking as well as highlight some further research directions.