Research On Transparent Security Of JPEG Image

With the developments of multimedia and network technologies, the confidentiality and authenticity of multimedia are attracting more and more attention. During the process of multimedia data protection, people always neglect their unique characters, such as the format of file, the syntax of stream, and the restrict of storage, which may lead to some side effects on data compressing, transmission, storage, play back and even signal processing functionalities. So the transparent encryption and authentication which are used to protect the security of data are attracting more and more attention. They can not only protect the security of data but also avoid destroying the multimedia data as much as possible in the procedures of coding and decoding, storage, transmission, file management and signal processing.The mainstream of image and video compressing standards are DCT and VLC coding based. Therefore, we make research in the transparent security of the still image standard JPEG in this thesis which is the representation of compressing standards. The main works are listed as follows:Firstly, make the definition of multimedia transparent security mechanism according to the needs of application.Secondly, the JPEG image encryption and authentication algorithms and their characters are investigated. A key management scheme is proposed according to the character of JPEG coding.Thirdly, deep analyses on stream cipher and index mapping encryption of FLC coding are performed. It is found that these algorithms have good transparent character but are fragile to content leakage attacks. So they can only be used on the occasions of high real-time and low security.Fourthly, we propose two kinds of two-dimensional chaotic maps image encryption algorithm, the advantages of which are (1) the maps can be formulated using equations; (2) The maps are sensitive to the change of key; (3) The maps have a large key space. Two-dimensional chaotic maps can not only be used to encrypt image in space, but also be used to shuffle the DCT blocks. The algorithms of chaotic maps can keep the transparent character of DCT blocks while enhancing their security after the process of shuffling the DCT blocks.Fifthly, we propose two kinds of two-dimensional chaotic maps, the advantages of which are: (1) the maps can be formulated using equations; (2) the maps are sensitive to the change of key; (3) the maps have a large key space. Two-dimensional chaotic maps can not only be used to encrypt image in space, but also be used to shuffle the DCT blocks. The security performance can be improved by employing DCT shuffling while the transparent character can be maintained.Sixthly, we propose and implement a new transparent security framework for JPEG that integrates transparent encryption, key management and lossless watermarking techniques.