Research On Digital Image Encryption And Digital Watermarking

The digital media has become a main way for information communication along with the wide use of network. At the same time, multimedia information security problems including copyrights piracy emerged as side effects of the popularity of digital representation and distribution over network. Information hiding, also called Steganography, digital watermarking technology and multimedia information encryption methods provide novel ways to solve these security problems for multimedia information. In this dissertation, we study the technologies and application of multimedia information security in the area of digital image encryption and digital watermarking. The main contributions of this dissertation are: 1. Digital Image Encryption An image encryption technique base on chaos sequence is proposed. Chaotic sequences have several good properties including the ease of their generation, the sensitive dependence on their initial condition and the statistics property of noise. We discussed an image encryption arithmetic base on chaotic sequences. We generate the real number value chaotic sequences by using the key value and disperse them into symbol matrix and transformation matrix. We implement the image encryption algorithm based on the technique of image scrambling transformation in special and frequency domain. Preliminary results are satisfactory. A new digital image matrix transformation is proposed and its application for image encryption is also discussed. We discuss its periodicity and inverse transformation. We proved that its inverse transformation has the same periodicity. A simple method to count the periodicity of matrix transformation is given. And their security is also discussed. Finally we propose its application in the area of digital image encryption. The new encryption scheme has the following properties: good security of encoding and decoding, high computation speed and robustness of anti-geometry transformation. 2. Digital Image Watermarking An algorithm for meaningful watermark is proposed. Most digital watermarking use pseudo random sequences as watermarks and so they only answer 'yes' or 'no' for detecting the watermark. In some application, embedding meaningful watermark is important. But there have many difficulties. We apply the theory and technique of image processing and computer vision to implement meaningful watermarkembedding. Preliminary results are satisfactory. A digital watermarking scheme base on image characteristics is proposed. The technique aim at improving the robustness of watermarking to ensure detecting the watermark even though watermarked image were attacked of the cut-and-replacement attack. Our watermarking scheme has the following properties: better robustness, anti-cut and anti-rotation. A public key digital image watermarking algorithm is proposed. Data owner can embed the identification into the original data and retrieve it from the watermarked data using his private key, while data user can detect the identification using the public key. The data user can't forge the private key and destroy or erase the identification that embedded into the original image by using public key. Experiment results show its security and robustness. A novel semi-fragile authentication watermarking scheme is proposed. We focus our discussion on how to generate the content-based watermark and embed the watermark into the original image by using the techn...