一种结合JPEG压缩编码的彩色图像加密算法

摘要

为了研究针对联合图像专家小组压缩标准(joint photographic experts group, JPEG)彩色图像特点的加密算法,综合选择加密和在编码过程中加密两种思路,提出了一种空域和频域结合的加密算法。首先在空域对8×8分块进行扩散置乱,然后利用边缘检测手段找出包含细节信息较多的重要分块,先加密所有分块中的直流(direct current, DC)系数,再选择重要分块中的一部分交流(alternating current, AC)系数进行加密,最后将分块重要性标记信息嵌入AC系数中进行传输。通过理论分析和大量实验证明,算法格式兼容,密文图像视觉效果好、色彩分布均匀；算法密钥空间大,密钥敏感性强,安全性良好。%To research the encryption algorithm for color joint photographic expert group (JPEG) image, by comprehensively choosing the selective encryption and the joint compression and encryption, an encryption algorithm combining with spatial domain and frequent domain for color JPEG image is proposed. The 8 × 8 blocks are first diffused on spatial domain, then the edge-detection method is utilized to find out the significant blocks containing abundant details. After encrypting all the direct current coefficients, part of alternating current (AC) coefficients in significant blocks are chosen to be encrypted. Finally the information about marking the significance of the blocks is embedded into AC coefficients for transmission. Theoretical analyses and experimental results show that the proposed algorithm is compatible with JPEG format. The cipher image has good visual quality and uniform color distribution. The algorithm possesses huge key space, strong key-sensitivity and good security.