基于块调制置乱的图像加密算法安全性分析

块调制置乱图像加密是加密域可逆信息隐藏常用的加密方法之一,能有效提高算法的隐藏容量和抵抗现有唯密文、已知明文等攻击的能力.针对块调制置乱图像加密,提出一种已知明文攻击条件下的密钥流估计方法.首先,定义图像差值块,分析指出块调制生成密文块以较高的概率保持差值块不变的特性.然后,提出一种伪差值图像构建、差值块立方均值索引查找等关键策略的块置乱密钥的快速估计方法.分析讨论了图像的差值块立方均值分布、分块大小对置乱密钥估计正确率的关系.最后,给出了提高图像加密安全性可能的解决方案.实验结果表明,明文图像的纹理复杂度和分块大小是影响块置乱密钥估计正确率和算法时间复杂度的主要因素;分块大小大于3×3时,图像块置乱密钥的估计正确率达到70%以上,密文图像的内容会被泄露.

Security Analysis of Image Encryption Algorithm Based on Block Modulation-Scrambling

Block modulation-scrambling image encryption is one of the common encryption methods for reversible data hiding in encrypted image(RDH-EI).It can effectively improve the embedding capacity of the algorithm and resist the existing ciphertext only and known plaintext attacks.For block modulation-scrambling image encryption,a key stream estimation method under known plaintext attack is proposed in this paper.First of all,the definition of image difference block is given,and it is pointed out that the ciphertext block generated by block modulation keeps the difference block unchanged with high probability.On this basis,a fast block scrambling key estimation method based on pseudo difference image construction and difference cube mean index search is proposed.The relationship between the cube mean distribution of the difference block and the block size and the accuracy of the scrambling key estimation is discussed.Finally,the possible solutions to improve the security of image encryption are given.The texture complexity and block size of the plaintext image are the main factors that affect the block scrambling key estimation accuracy and algorithm time complexity.When the block size is larger than 3×3,the accuracy of all test image block scrambling secret key estimation is more than 70%,at this time,the content information of ciphertext image is seriously leaked.