Secure Multimedia Encoding Schemes Based on Quadtree Structure
基于四叉树的多媒体安全编码方案

For multimedia data is often voluminous and requires real time operations, multimedia encryption algorithms should meet extra requirement compared with textual data encryption algorithms. Traditional algorithms such as DES, RSA, can't meet some real time requirement. Some selective encryption algorithms can't completely keep the file format and compression ratio unchanged. In order to meet such requirement, the algorithms should combined encryption process with encoding process. Due to the wide application of quad tree structure in image or video encoding, two types of quadtree permutation algorithms are proposed here. They are used in quadtree based image encoding, wavelet zerotree encoding (EZW, SPIHT), and quadtree based fractal image or video encoding. The encryption algorithms combine encryption with compression, and have some advantages. Firstly, it is secure, and the encryption result is too confused to be understood. Secondly, it keeps the file format unchanged, and thus it is easy to operate compressed and encrypted data directly. Thirdly, it keeps the compression ratio unchanged, that is to say that the encryption operations do not produce extra data. Lastly, it is fast and can meet real time requirement.