| Abstract |
With the development of the computer and network technology, digital media information is used in many fields more widely, e.g., the industry, medical treatment and academic research. As a result, the... corresponding security problem of the digital media information becomes increasingly significant. Moreover, to reduce the volume of the information for the transmission, the digital media information, in general, does the compression as one procedure. Based on this background, there are three kinds of methods for the secure communication of the digital media information. The traditional way is that the digital media information is first compressed to reduce the redundancy, and then encrypted to mask its meaning. However, in some application scenarios, the sender of the digital media information hopes encrypting the original data firstly and the network provider may compress the encrypted information without knowing any knowledge on the original and the corresponding data. Therefore, the second method which does the encryption followed by the compression has been attracted as the considerable research interest recently. Specially, for the second method, the research of the corresponding encryption algorithms is one of the main research topics in the digital media security. The third method is that the compression of the digital media information and the corresponding encryption can be achieved simultaneously. This research always considers the revision of the traditional compression algorithm (e.g., the Huffman coding and arithmetic coding). The purpose of it focuses on the reduction of the time and computation of each operation (i.e., the compression and encryption), and this kind of research makes the system flexible for the advanced digital media processing. According to the above analysis, it can be found that the second method and the third method are two interesting topics in the field of the digital media security. In fact, there have been many encryption algorithms belonging to these two methods which are proposed for protecting the secrecy of the digital media information. Correspondingly, the security analysis of the proposed algorithms also becomes important before they are employed in practice. In this thesis, we investigate the security of some encryption algorithms about the digital media. In particular, as the still image is one of the main vehicles of the digital media information which causes that there have been many proposed image encryption algorithms, our security analysis primarily focuses on the still image related encryption algorithms. In our analysis, we try to identify some properties in the different encryption algorithms which can be exploited to break the corresponding ciphers.show more
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