| The rapid development of the computer network provides great convenient for the use and spread of information resource, while in the same time, the problem of information security is serious. How to protect the security of message in the process of transformation has become the significant task for people to solve. The traditional method is to encrypt the message. With the improvement of processing speed of CPU and the development of parallel algorithms, it is not an impossible thing to decrypt the encrypted message with supercomputers. Therefore searching for a novel method to solve the problem above is one of the important aspects that people face in the information age.Information hiding technique provides another way to solve the problem above. In contrast with encryption, the existence of communication process and both communication sides is hided in the information hiding technique. Even if the cover is intercepted by illegal users, the secret message can not be revealed because they do not know whether the secret message exists or not. The encryption method make the secret message into confused code, and only some one who hold the right key can access the secret information. When the code is captured by the sniffers, they may determine that they have got another form of the secret and the next step is to decrypt the secret from the disordered code.Recently, the research of digital watermarking is emphasized, and the stegnaography that is applied to the secret communication is also focused. In this dissertation, some algorithms of data hiding based on the digital image, text and audio are developed from the practical points of view. The main contributions of the dissertation are summarized as follows.1. Digital image scramblingDigital image scrambling comes from the algorithms used by the classical cryptography in the early time. Digital image is considered as a two dimension matrix, and when the permutation transform is executed, the digital image is disturbed and the way for protecting the digital image is obtained. Similar to cryptography, we can use the key for scrambling the image, and only some one who possess the right key can access the right image.In this part, the scrambling methods based on cryptography and chaos sequences are presented, and the encryption methods used in the TV are applied to the digital image scrambling. Simulation results show that the methods we presented have better performance.2. Data hiding in the digital imageCombined with HVS(Human Visual System), we can put secret message in the image without degrading the quality for its redundancy and to secure the information. The message to be transferred can be image or text file, and can be hided in the space domain or frequency domain of the image.According to the feature of the human vision, we present the hiding methods based on image variance, image flatness measurement and fuzzy classification, respectively.And the techniques based on relationship between pixels, difference matrix and cryptography are also given. Two hiding methods, backup hiding and camouflage hiding, are proposed too. All methods above are operated in the space domain. In the frequency domain, we analyse the information hiding technique based on DCT. We present improved adaptive hiding method, odd even embedding technique, improved amalgamation and difference matrix hiding method in the DCT domain. We describe the process of information embedding and extraction, and analyse the robust of the algorithms above in detail. The necessary content of digital image, which is transported, is also discussed. 3 Data hiding for authenticationWe can divide the information in the network into two kinds: one is that can stand slight tamper, for example, image, video etc., and we can apply it as long as the tamper does not affect its quality and value. The other kind is the text. When the text is tampered, we can not get the right message if it is encrypted. The same problems also exist in information hiding, and how to detect the tamper and...
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