Reasearch On Fast Algorithm For Mutimedia Encryption

With the development of computing and network technology, multimedia data are used more widely. At the same time, the information security for multimedia data becomes increasingly important and cryptography is the primary method to resolve it. Contrast to texts, multimedia contents contain usually huge volume of data, which make their encryption become very slow and power-consuming. If we use traditional encryption algorithms on multimedia data, it's difficult to satisfy the need of realtime, and it will change the format of the data, so we should use special encryption algorithms on multimedia data. This paper focuses on the approaches to improve the realtime of encryption based on the characteristics of the application, under the condition that those approaches satisfy the security requirements. Some of the conclusions of this paper are listed as follows.1. The coding format of all kinds of multimedia data such as JPEG, MPEG, MPEG-2, etc are being analyzed, and the layered format and coding flow of JPEG and MPEG-2 are well grasped.2. The feature of current multimedia encryption algorithm is pointed out by theoretical and experimental study.3. A spatial image encryption algorithm based on quad-tree is proposed. For better security performance, the improvement to this algorithm has been done by analyzing the key space of the internal permutation. By emluator and analysis it is proved that the algorithm have characteristic of small amount of encrypted data and low-complexity of operation, and meet the requirements of the need of realtime for low-operation ability equipment.4. A MPEG-2 file encryption algorithm based on position file is proposed for video server. This algorithm can reduce the volume of encrypted data greatly by employing selective encryption, and evidently improve the performance of fault tolerance in network condition with improved CTR mode. The most important thing is that the algorithm can remarkably speed up the process of encryption and decryption of MPEG-2 by using the position file. The experiment and analysis show that this strategy of saving time at the cost of memory can significantly increase the average processing speed in multi-user environment, which makes this algorithm practically useful.Finally, the dissertation is concluded. Some problems as well as further work are also given.