Research On Video Encryption Algorithm Based On H.264 Coding Standard

Video is widely used in many old and new areas by virtue of its unique advantages.These areas include political,military,medical,network streaming media and so on,but in the meanwhile,to ensure the security of video,as an efficient information and communication media,is increasingly being taken seriously.H.264 has become the most popular coding standard by its efficient compression and better network adaptability,but the encryption algorithm for H.264 is usually unable to resolve the contradiction among security,encryption efficiency,compression efficiency and format compatibility effectively at a time.So to research the new encryption algorithm for H.264 is of great significance for extending the video applications and protecting the security of the video data.This dissertation proposes an encryption selection decision model,which can be in parallel with the rate-distortion cost calculation,on the base of the depth analysis for the characteristic of syntax elements in the stream and intra-prediction.Three syntax elements,which are the intra-prediction mode,the tailing coefficient and the amplitude quantized sign bit,are encrypted in the entropy coding stage by chaotic keys system based on double logistic mapping in the blocks which are filtered out by encryption selection decision model.To encrypt those three syntax elements at a once achieves to hide the original video information effectively.Besides,we proposes an encryption algorithm for inter frame in this dissertation,which extends the key space through the polar coordinate transformation and disrupts the trajectory sufficiently,on the base of the motion vector cipher diffusion.This algorithm constraints the orthogonal direction as candidate cipher domain and encrypts the radian under polar coordinate,H.264 encoder caches real motion vectors as the reference information of the motion compensation to touch off the cipher diffusion of motion vector,which improves the encryption effectThe simulation results showed that the algorithm for intra frame has expressed very well in the four aspect which are the security,the encryption efficiency,the compression ratio and the amount of data encrypted under the premise of ensuring format compatibility.On the other hand,the encryption algorithm for motion vector disrupted the trajectory effectively and both data expansion and encryption delay are within the range of the requirements of the vast majority of real-time applications in terms of performance.So both of those encryption algorithm holds a high practical value.