Research And Implementation Of Chaos-based Video Encryption Algorithm For H.264

With the rapid development of multimedia technology and network technology, the network video has been applied to many fields, such as economy, military, education, entertainment and so on. Video information has a large number of data, high real-time requirement and complex structure so that an efficient compression technique is needed to deal with it to meet people’s growing demand for high quality video day by day. The H.264video compression encoding technology has been widely used because of it has high compression efficiency, robustness and network adaptability. Therefore, it has important theoretical significance and application value to research the H.264video encryption technology.According to the characteristics of the H.264standard, this thesis uses chaos encryption technology to design four kinds of encryption algorithms which combines the compression with encryption. Among them, the DCT coefficients encryption algorithm based on4X4integer transform uses improved encryption-diffusion model to encrypt the DCT coefficients of video image residual; The encryption algorithm based on CAVLC encrypts the symbols of trailing-coefficients and the numbers of zeros before every non-zero coefficients in CAVLC encoding process; The4×4luma intra prediction model word encryption algorithm encrypts the rem_intra4x4_pred_mode which is a variable in intra prediction model word encoding process, according to the intra prediction model word encoding theory; The motion vector symbols encryption algorithm uses pseudo random binary sequence generated by chaotic system to encrypts the symbols of luma motion vector. In the implementation phase, given the demand of security, real-time and the invariance of compression ratio, this thesis designs reasonable encryption scheme for every kind of frame, such as I frame, P frame or B frame, according to their characterstics. Among them, the I frame is encrypted by DCT coefficients encryption algorithm based on4X4integer transform and4×4luma intra prediction model word encryption algorithm, In the P frame, the P block is encrypted by encryption algorithm based on CAVLC and the motion vector symbols encryption algorithm, meanwhile, the I block is encrypted by4X4luma intra prediction model word encryption algorithm. Being similar to the P frame, the I bolck of B frame is also encrypted by4X4luma intra prediction model word encryption algorithm, but its B block is only encrypted by motion vector symbols encryption algorithm.In order to evaluate the performance of encryption algorithms, this thesis tests the four encryption algorithms on the JM.86of H.264, and compares them with H.264standard as well. The results show that the encryption algorithm can meet the requirement of visual effect, its expansion ratio of Compression controls around12%, and its expansion ratio of time is about17%. The theoretical minimum key space of the encryption is115bit. It has certain advantage in every performance compared with the traditional encryption, such as DES, AES. Particular, its encryption efficiency improves greatly so that it can meet the real-time requirement of video transmission in the Internet.