Abstract: In order to solve the problem that the leakage of privacy content of images in the process of public channel transmission results in endangering information security, a new encryption method of greyscale image was proposed. The iteration of coupled logistic map was used to generate two-dimensional chaotic sequences. One of the sequences was used to generate the coefficients of cat map. The another was used to scramble the pixel positions. The traditional image encryption method based on cat map was used to encrypt the image pixel position, while the proposed encryption method was used to adopt different cat map coefficients for different pixel groups, so as to transform the grey value of each pixel in the group. In addition, bidirectional diffusion was adopted by the method to improve the security performance. The proposed method has simple encryption and decryption processes, high execution efficiency, and no limitation for the image size. Security analysis shows that the proposed encryption method is very sensitive to secret keys, and has good stability under multiple attack methods.

Key words: image encryption, cat map, chaotic iteration, coupled logistic map, bidirectional diffusion

摘要： 为解决在公共信道传播过程中由于图像中的隐私内容泄漏从而危害信息安全的问题，提出一种新的灰度图像加密方法。新方法采用coupled logistic映射迭代来产生二维混沌序列，其中一个序列用于生成猫映射的系数，另一个用于置乱像素位置。传统的基于猫映射的图像加密方法是加密图像像素位置，而新的加密方法是对每个像素组使用不同的猫映射系数，从而变换组内每个像素的灰度值。除此之外，方法还采取双向扩散提高安全性能。所提方法加密解密过程简单，执行效率高，对图像尺寸没有要求。安全性分析表明，该加密方法对密钥十分敏感，且在多种攻击手段下都具有较好的稳定性。

关键词: 图像加密, 猫映射, 混沌迭代, coupled logistic映射, 双向扩散