On Fast Multimedia Encryption Algorithms

With the development of multimedia technology and network technology, multimedia data are used more and more widely. In order to protect multimedia data, some encryption algorithms have been studied. In this paper, the fast multimedia encryption algorithms are studied, and their performances are analyzed and tested. Some of the conclusions are listed as follows.First, the security of Fridrich's chaotic cipher is analyzed thoroughly according to brute-force space, parameter sensitivity, known-plaintext attack and select-plaintext attack. Additionally, the relationship between the security and computing complexity is studied, and some means are presented to strengthen the cryptosystem. Based on the above analysis, a block cipher based on Standard map is presented, which supports plaintexts with various lengths, has low cost, and is thus suitable for multimedia encryption.Secondly, a selective encryption model is proposed, together with some encryption principles and their verification. As examples, the selective encryption algorithms combined with fractal image coding, JPEG2000 and MPEG2 are presented. Some properties are obtained, such as low cost, high security, keeping file format unchanged and supporting direct operations (browsing, cutting, etc.).Thirdly, an encryption model combined with compression process is proposed, whose performances are analyzed. As examples, the encryption algorithms are presented, which combine with JPEG, MPEG2 and JPEG2000. They often realize compression and encryption at the same time, keep low cost, and support such direct operations as browsing, cutting, bit-rate control or recompression. These properties make them suitable for some applications with low security, real-time operation and direct operation requirements.Fourthly, an improved perceptual cryptography is presented, which supports direct bit-rate control. During compression process, the ciphertext's quality is controlled by the encryption quality factor. Combined with JPEG, MPEG2 and JPEG2000, several perceptual encryption algorithms are constructed and analyzed. These algorithms are suitable for such applications as video-on-demand, audio-on-demand and so on.Fifthly, a secure multimedia transmission scheme is proposed, which combines compression, encryption, authentication and error-correction coding. The sensitive data are...