An improved image encryption algorithm for spatiotemporal chaotic system is proposed.In this algorithm,a local feedback to the chaotic system is used to adjust the spatiotemporal chaotic system,an improved spatiotemporal chaotic system is used to calculate the control parameters,and then the scrambling operation can be completed.The diffusion operation is therefore carried out to complete the colour image encryption process.Based on the simulation of Lena image and the related performance analysis,experimental results show that the correlation among the adjacent pixels in the horizontal,vertical and diagonal directions is low,and that the average information entropy of the three components of R,G and B is 7.993 8,which is close to the expected value in the maximum disorder state.Thus,a better encryption effect is achieved.The analysis of its anti-statistical attack performance and differential attack show that the pixel values of plain text image in R,G and B is relatively inhomogeneous,and that the pixel values of the cipher text image in R,G,B is evenly distributed.The number of pixels rate of R,G and B is 99.60％,99.59％ and 99.62％ respectively,and the uniform average change index of R,G and B is 33.45 ％,33.47％,and 33.47％,which are close to the optimal value.The improved spatiotemporal chaotic system can therefore effectively resist statistical attack and differential attack.%提出了一种改进时空混沌系统的图像加密算法.该算法通过对混沌系统加入局部反馈来调节时空混沌系统,利用改进的时空混沌系统来计算控制参数,完成置乱操作,然后对其进行扩散操作,完成彩色图像的加密过程.通过对Lena图像仿真并进行相关性能分析,结果表明,加密图像在水平、垂直和对角方向的相邻像素点的相关性较低,在R,G,B三个分量的平均信息熵值为7.993 8,接近最大无序状态下的期望值,加密效果较好;在对其进行抗统计攻击性能分析及抗差分攻击对比分析中,明文图像像素值在R,G,B三个分量上的分布相对不均匀,而密文图像的像素值在R,G,B三个分量上都呈现均匀分布,其R,G,B三个分量的像素数改变率分别为99.60％、99.59％、99.62％,其R,G,B三个分量的统一平均变化度分别为33.45％,33.47％,33.47％,均接近最优值,改进的算法能有效地抵抗统计攻击和差分攻击.
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