Abstract: In order to effectively improve the image encryption effect and safety, based on studying image encryption algorithm based on chaotic systems and bit operations, an improved algorithm of digital image encryption algorithm was proposed. Firstly, Logistic map was used to generate chaotic sequences, constructing row and column vector to scramble pixel position by the proposed algorithm. Secondly, another piecewise nonlinear Logistic sequence was applied to construct gray scale scrambling amplification factor to scramble the image gray scale, meanwhile the two processes were iteratively done . The mentioned algorithm made not only the key space increase and gray histogram uniform, but also the pixel correlation weaker and the operation speed faster than traditional algorithms. The experimental results show that the improved algorithm has good encryption efficacy and safety.

Key words: chaotic map, image encryption, position scrambling, pixel bit, piecewise nonlinear mapping

摘要： 为了有效改进图像加密效果及其安全性，在对基于混沌系统及位运算的图像加密算法进行研究的基础上，提出一种改进的数字图像加密算法，该算法首先采用Logistic映射产生混沌序列构造行、列置乱向量进行像素位置的置乱，再利用分段非线性Logistic产生的序列构造灰度置乱放大因子，对图像进行灰度置乱,且对两个过程进行迭代操作。该算法不仅密钥空间增大，灰度直方图更加均匀，而且像素相关性变弱，运算速度较传统算法更快。实验结果表明，改进算法具有良好的加密效果和安全性。

关键词: 混沌映射, 图像加密, 位置置乱, 像素位, 分段非线性映射