Research On Steganographic Theory And Techniques

The multimedia steganography is a new research field developed in recent years in spite of the long history of steganography. The essential difference between steganography and cryptology is that the latter conceals the content of information itself while the former conceals the very existence of information. With the development of multimedia steganography, a wholly new approach with considerable developing foreground is exploited for the information security technology. The research of multimedia steganography is not maturational either on theory or on technique at the present time, lacking systematic theory foundation and impartial uniform performance-testing and evaluating system. So it should be very meaningful to establish an integrated theory system to conclude some crucial problems and analyze them systematically.In this dissertation, some issues involved in multimedia steganographic theory and techniques are studied, which are detailed as follows:(1) A general mathematical model of steganography is proposed. This model covers most models based on the specialties either of applying steganographic key or of encountering attacks proposed in other papers .(2) The issues on steganographic theoretic security and capacity are studied systemically for the first time. A matter-off-act information security hierarchy concept is introduced. Propose and attest the adequate and necessary existing condition of undetectable steganographic system based on information theory. The research result can point out the orientation of designing a safe secret communication system. One kind of method to define and evaluate the steganographic theoretic security is introduced. Finally, the formula of steganographic capacity under passive attacking or active attacking is described.(3) Under analyzing the maneuver of information hider and attacker in a steganographic system, the sets of strategy for hider and attacker is set up. The methods to establish the model of a steganographic system based on game theory and then to solve the optimal strategy are described.(4) The issue on information authentication in a steganographic system is analyzed and the mathematical definitions of three kinds of active attacking are described using complexity theory. Then two steganographic schemes with the ability of information authentication are designed by combining with Hash function and digital signature algorithm. Finally, the authentication security of the two schemes under active attacking istheoretical ratiocinated.(5) A public key steganographic system using gray image as the cover-object is developed. While hiding quite large amount of information, the stego-image maintains quite similarity to cover-image in human visibility and statistical analysis. The systematic security is evaluated with theory and experiment.(6) Based on analyzing the specialty of binary image information hiding, a secure and high capacity algorithm for hiding data into binary images is proposed.(7) Introducing the image transform idea into the designing for palette-based image data hiding algorithm, a wavelet based algorithm for hiding information into palette-based image. This algorithm is of quite high security and robustness and able to send the secret message to the receiver in security and integrity under both the passive and active attacking.Finally, the thesis is concluded by pointing out some open issues on the research of information hiding and steganogaphy as well as highlight some further research directions.