A fast selective encryption scheme for H.264/AVC video with syntax-preserving and zero bit rate expansion

H.264/AVC is the most widely used video-coding standard today, and designing selective encryption (SE) algorithms for H.264/AVC has drawn extensive attention. Unfortunately, existing SE schemes cannot provide a good balance between security, bit rate, and encryption efficiency. In this paper, we propose a fast H.264/AVC SE scheme with syntax-preserving and zero bit rate expansion. To produce heavy visual distortion, both prediction and residual syntax elements, including intra-prediction mode, motion vector difference (MVD), TrailingOnes, and Level, are selected for encryption. Based on the hash function SHA-224, their values are encrypted using a plaintext-dependent keystream sequence generated by the hyperchaotic Lü system. To keep format compatibility and the same bit rate, different encryption strategies are designed according to the encoding characteristics of each syntax element. Besides, reversible data steganography is employed to embed the hash value into the encrypted MVD by bit. Therefore, the hash value can be transmitted or stored together with the encrypted video, increasing the practical applicability of the algorithm. Furthermore, if the wrong hash value is extracted, decryption will fail, thus further enhancing the encryption strength of our scheme. Experimental results demonstrate that the proposed algorithm has a key space of size 2212\documentclass[12pt]{minimal} \usepackage{amsmath} \usepackage{wasysym} \usepackage{amsfonts} \usepackage{amssymb} \usepackage{amsbsy} \usepackage{mathrsfs} \usepackage{upgreek} \setlength{\oddsidemargin}{-69pt} \begin{document}$$2^{212}$$\end{document}, and the average PSNR, SSIM, and time expansion are lower than 13 dB, 0.22, and 0.06%, respectively. Thus, our scheme provides both a high level of security and high efficiency.