为了解决现有图像加密算法存在随图像尺寸变大导致加密时间迅速增加的问题, 采用基于logistic和Arnold映射的改进加密算法实现了快速图像加密算法的优化。该算法基于两种混沌映射对原文图像进行像素置乱和灰度值替代, 像素置乱是按图像大小选择以H个相邻像素为单位进行, 通过适当调整H的取值实现加密时间优化; 灰度值替代是利用Arnold映射产生混沌序列对置乱图像进行操作而得到密文图像。结果表明, 对于256×256的Lena标准图像, 加密时间降低到0.0817s。该算法具有密钥空间大和加密速度快等优点, 能有效抵抗穷举、统计和差分等方式的攻击。

In order to solve the rapid increase of the encryption time because of the increasing image size in the existing image encryption algorithm, the optimized encryption algorithm based on logistic and Arnold mapping was used to achieve the optimization of the fast image encryption algorithm. The algorithm was based on two kinds of chaotic maps to the original image, pixel scrambling and gray value substitution. Pixel scrambling was to select the H adjacent pixels according to the image size, appropriately adjust the H value and realize the encryption time optimization. Gray value substitution is to generate chaotic sequences by Arnold mapping, operate the scrambling image and get the cipher image. The results show that, for 256×256 Lena standard images, the encryption time is reduced to 0.0817s. The algorithm has advantages of large key space and fast encryption speed, and can effectively resist the attack of exhaustive, statistical, and differential means.