Abstract
Nowadays, many cryptographic algorithms have been implemented for security purposes in communication systems. The problem of security has become an important issue in many applications, especially in multimedia applications. In this thesis, the security-related problems of particular multimedia applications are addressed and various cryptographic algorithms are then implemented in known or adapted procedures to solve such problems. The range of issues considered can be classified as follows: Firstly, the problem of certifying the integrity of images from digital cameras such as for video surveillance is addressed and a scheme designed for this purpose is presented. Secondly, the problem of user authentication in one-way broadcast applications such as pay-TV service is indicated and a key distribution scheme based on the smart card and set top box combination technique is designed to solve such a problem. Thirdly, the problem of the right of privacy in communications between two parties is discussed and a scheme based on cascading algorithms is then used as a solution. Fourthly, the problem of encrypting a large amount of multimedia data such as a video stream is addressed and a low-complexity encryption method using block ciphers is designed to cope with this kind of data. Finally, the problem of secure distribution of copyright data is studied and two different approaches are then proposed. The first approach is based on the idea that the output from the watermarking scheme should be in encrypted form. The second approach is based on the idea of watermarking an encrypted copy. All the proposed schemes have been published in some forms and therefore subjected to outside review of their security.