基于余弦-指数混沌映射的分块图像加密算法

为平衡混沌映射中结构与性能的关系，保证加密系统安全性，提出一种基于余弦-指数混沌映射的分块图像加密算法。首先，通过非线性指数项对引入了Tent种子映射的余弦映射进行调制，构造新型余弦-指数混沌映射，并利用SHA-256函数产生与明文相关的密钥，生成随机性较强的混沌序列，实现一次一密；然后，基于拉丁方和位级转换，通过两轮拉丁方索引和比特位拼接，分别设计双重拉丁方和扩展比特位算法，并结合二维约瑟夫序列，对块间预置乱后的明文进行块内置乱，实现不同分块的差异化置乱；最后，基于Zig-Zag变换，采用环状仿Zig-Zag变换设计交叉Zig-Zag变换方法，将中间密文与混沌序列进行双向非线性扩散，实现同时改变像素位置与大小，完成图像加密。实验结果表明，该算法密钥空间大，能有效抵御差分分析和统计分析等典型攻击，具有较好的加密效果。

A block image encryption algorithm based on cosine-exponential chaotic map

In order to balance the relationship between structure and performance in chaotic map and ensure the security of the encryption system,a block image encryption algorithm based on cosine-exponential chaotic map is proposed.Firstly,a new cosine-exponential chaotic map is constructed by modulating the cosine map with the introduction of the Tent seed map through the non-linear exponential term,and the SHA-256 function is used to generate the key associated with the plain-text,generating chaotic sequences with strong randomness to achieve one-time pad.Then,based on the Latin square and bit-level transformation,the double Latin square and extended bit algorithm are designed through two rounds of Latin square indexing and bit stitching,respectively,and combined with two-dimensional Josephus sequences,to scramble the inter-block pre-scrambled plain-text within blocks,achieving differential scrambling of different blocks.Finally,based on the Zig-Zag transform,the cross Zig-Zag transform method is designed using a circular imitation Zig-Zag transform,which diffuses the intermediate cipher-text with the chaotic sequence nonlinearly in both directions to achieve simultaneous change of pixel position and pixel value to complete the image encryption.The experimental results show that the algorithm has a large key space and can effectively resist typical attacks such as differential analysis and statistical analysis,and has a good encryption effect.