使用進階加密標準之一H.264/AVC碼流相容選擇性加密方法

Abstract

The H.264 video coding standard has been widely applied to multimedia data transmission. To prevent the contents of video from being recognized by someone unauthorized, providing sufficient security to H.264 has become more and more important. In this thesis, an improved H.264/AVC video encryption method is proposed. As compared with the Shahid’s method, more data are encrypted. And this makes the outcome more desirable. In the proposed scheme, selective encryption (SE) is performed in the motion vector difference (MVD), delta quantization parameter (delta QP), and the context-based adaptive variable length coding (CAVLC) modules. Owing that the encrypted stream should be decoded correctly before decryption, a format-compliant method is presented. Furthermore, in order to keep the bitrate unchanged, keeping the same stream length is another important characteristic of our proposed scheme. Since there is no escalation in bitrate, the proposed encryption algorithm is suitable for real-time multimedia streaming over heterogeneous networks. The encrypting key is generated by using the advanced encryption standard (AES) algorithm, and every frame has its own unique key. Four benchmark video sequences with different combinations of motion, texture and objects were used for experimental evaluation of the proposed scheme. The structural similarity (SSIM) index, a reference value to image quality, of the proposed scheme is 0.202 which is lower than 0.233 of the Shahid’s scheme. The key security is shown reliable under the test of only 1 bit change. The extra computation needed by our scheme is less than 0.5%, so it is feasible for real-time transmission. The above performance on security and sensitivity demonstrates that our proposed scheme is a good candidate for practical applications.