Studies On Visual Security Of Content-based Visual Media Encryption

The rapid development of information technology and network communication technology is greatly speeding up the access and dissemination of visual media data. The characteristics of visual media data, a wide range of applications and use in certain occasions, result in the appearance of some special security issues, such as the visual security issues. Visual security of the visual media is an important part of the theoretical basis of visual media content encryption security. Therefore, the study of the visual security issues in the visual media content encryption, to resolve the contradiction between application promotion and securities in visual media content encryption, has important significance and research value.This thesis focuses on the visual security issues of visual media data encryption. Combined with the pixel intrinsic properties of visual media data and ciphertext stream characteristics of post-data content encryption, an effective visual attack method of the visual media content encryption and an objective assessment method of visual security for cipher image are proposed. On this basis, the visual media content encryption security model with cryptanalysis security and visual security is proposed, which guides the design of the visual media content encryption algorithm and system to meet the application requirements. The main contents are as follows.(1) Visual media content encryption security model. Based on the characteristics of visual media data and visual media application requirement, the visual media content encryption model is proposed for solving the several key issues involved in content security in the visual media content encryption. In this model, through analysis and selection of visual media data, visual security objective evaluation method, other attack methods beside cryptographic attacks and performance metrics construction of visual media content encryption, the theory and design methods of cryptanalysis security and visual security of visual media content encryption are obtained.(2) Objective evaluation method of visual security for cipher image. Based on the research status and existing problems of visual security evaluation in visual media content encryption, combined with information theory and the cryptography theory, the concept of the ideal security image is presented. And then an objective evaluation algorithm of visual security based on local information entropy for cipher image is proposed, which evaluates the damaging, scrambling, masking extent of visual information in cipher image through objective method and index. The study provides objective and quantitative methods for visual security of visual media content encryption.(3) Visual analysis attack beside cryptographic attacks. The visual media encryption algorithm not only studies classic cryptographic attacks in traditional cryptography, but also studies other attack methods based on the data characteristics of the visual media. After analysis of the data stream characteristics before and after visual media content encryption, the concept of visual analysis attack is proposed, following the basic idea and theoretical model of visual analysis attack method is presented. Based on this, a visual attack method for the DC coefficient encryption algorithm is presented. This attack method can effectively reduce image distortion of the cipher image with low computational overhead and complexity instead of deciphering the key of the encryption algorithm. It is confirmed the necessity and feasibility to research on visual analysis attack method.(4) Visual security performance evaluation in the chaotic encryption. For the problem of performance evaluation in image encryption algorithm based on chaotic system, visual security objective evaluation algorithm is introduced to the performance analysis of the chaotic image encryption, using visual security objective evaluation algorithm to evaluate the performance of the control parameters in the chaotic image encryption system, and using visual security objective evaluation algorithm to evaluate cipher image encryption effect after through chaotic image encryption. Experiments and analyzes confirms the effectiveness and simplicity of the visual security objective assessment method when it is used to evaluate performance of chaotic image encryption algorithm.This thesis focuses on the current application requirements of visual media, explores how to solve the security issues of visual media data in an open environment from the point of view of visual media content encryption and security evaluation. Firstly, the security model of visual media content encryption is proposed, which constructs theoretical framework of cryptanalysis security and visual security of visual media content encryption. Afterwards, considering encryption method based on the key content, and combination with analysis of importance of key content in visual media, an objective assessment method of visual security for cipher image based on visual perception of the visual media is proposed. At the same time, the theoretical model of visual analysis attack method and its method example is presented. In addition, the introduction of visual security objective assessment method into the chaotic image encryption system is used to evaluate the performance of the chaotic image encryption algorithm.