Abstract: An image encryption scheme based on composite chaotic system was proposed. The encryption system used the one-dimensional Logistic chaotic maping and the three-dimensional Lorenz system to produce chaotic sequences, and chose different ways to deal with scrambling transformation and gray transformation for each pixel according to the structural characteristics of the image itself. The security analysis shows that the proposed image encryption scheme provides higher efficiency and larger key space, and it is very sensitive to the key and the plaintext. It is characterized by excellent diffusion and confusion properties, which can resist the known-plaintext attacks and chosen-plaintext attacks.

Key words: Logistic mapping, Lorenz system, scrambling transformation, gray transformation, security analysis

摘要： 提出了一种新的图像加密算法。该算法使用一维Logistic混沌映射与复杂的三维Lorenz混沌系统复合生成混沌序列加密矩阵，根据加密矩阵和图像的自身特征，对每个像素点选择不同的方式进行置乱变换和像素灰度变换。安全性分析表明，该算法加密效果良好，加密效率较高，对密钥及明文均十分敏感，密钥空间较大，且扩散性和扰乱性比较理想，能够抵御已知明文攻击和选择明文攻击。

关键词: Logistic映射, Lorenz系统, 置乱, 灰度变换, 安全性分析