基于图像重组和比特置乱的多图像加密

针对现有多图像加密算法只能同时加密多张同类型同大小的图像,适用范围不广、实用性差等问题,提出一种基于图像重组和比特置乱的多图像加密算法.该算法通过将任意数量、不同大小和不同类型的图像重新组合成新多灰度图,一次完成同时加密,极大提高了加密效率和适用范围.首先,依次提取所有待加密图像像素值重新组合出N张m×n新灰度图,并将其转化成m×n×8N二进制矩阵.然后,采用3D比特置乱方式,对高位页进行行列比特置乱,低位页进行整页比特置乱.最后,进行异或扩散操作,得到密文图像.高低位分开置乱提高了算法的抗噪声能力,最终密文信息熵达到7.999以上,很好地掩盖了明文的统计特性.构造一种新型Logistic与广义三阶Fibonacci级联的混沌系统产生随机序列,增加了初值和控制参数范围,扩大了密钥空间,使其达到8×10^84以上,极大地提高了抗穷举攻击能力.既提高了序列随机性,又同时保留了低维混沌系统的快速性.结合明文哈希值(SHA-256)产生密钥,明文像素值发生微小改变后密文像素值变化率达到0.996以上,极大地提高了的明文敏感性和算法抗选择明文攻击的能力.实验分析表明,提出的多图像加密算法安全性高、实用性强.

Multiple-image Encryption Based on Image Recombination and Bit Scrambling

Aiming at the problems that the existing multiple-image encryption algorithms can only encrypt multiple images of the same type and the same size at the same time,which limits the scope of its application and practicality,a multiple-image encryption algorithm based on image recombination and bit scrambling was proposed.By recombining the images of any number,any type and any size into the new multiple-gray scale images,the algorithm can complete simultaneous encryption at one time,which greatly improved the encryption efficiency and application range.Firstly,the pixel values of all images were extracted to be encrypted in turn and were recombined into N new gray-scale images of m×n size,which were converted into m×n×8N binary matrix next.Then,3D bit scrambling is adopted to scramble rows and columns for high binary pages and the entire pages for low binary pages.Finally,the ciphertext image was obtained by XOR diffusion operation.The high-low separate scrambling improves the anti-noise ability of the algorithm.The information entropy of the final ciphertext was above 7.999,which well covered up the statistical characteristics of the plaintext.A new type of Logistic-Fibonacci cascade chaos was constructed to generate random sequences,which increased the range of initial values and control parameters,expanded the key space to over 8×10^84,and greatly improve the ability to resist exhaustive attacks.The randomness of the sequence was improved,while the rapidity of the low-dimensional chaotic system was preserved.Combining with the plaintext hash value(SHA-256)to generate the key,the change rate of the ciphertext pixel value reached more than 0.996 after the plaintext pixel value was slightly changed,which greatly improved the sensitivity of the plaintext and the ability of resisting the selective plaintext attack.Experimental analysis show that the proposed multiple-image encryption algorithm has high security and strong practicability.