将信息熵与图像的分块处理思想相结合,提出了一种基于分块信息熵方差的图像置乱程度评估方法.在详细阐述评估方法基本原理的基础上,通过仿真实验对同一图像基于Arnold变换的像素位置置乱、基于Logistic混沌映射的像素灰度值置乱及二者级联的像素位置与灰度值均置乱的3种图像置乱方式下的置乱程度进行评估和分析,并验证了所提方法的正确性与有效性.应用该方法进一步对多幅不同图像在同一加密算法下的密文图像的置乱程度进行评估,结果表明所提出的方法具有与原图像无关的特点,可以用于加密算法的安全性评估.文中方法原理简单,实现容易,且无需原图像参与,具有较好的实用性.

In this paper,by combining the information entropy with the image blocking,an evaluation method of image scrambling degree based on block information entropy variance is proposed.The basic principle of the evaluation method is elaborated,and some simulation experiments are carried out to evaluate and analyze the degrees of the pixe llocation scrambling based on the Arnold transformation,the pixel gray value scrambling based on the Logistic chaotic mapping and the Arnold-Logistic cascaded pixel location and grays crambling,respectively.The results show that the proposed method is correct and effective in evaluating the image scrambling degree.Moreover,further experiments on different images encrypted by the same algorithm show that the proposed method is suitable for the security evaluation of encryption algorithms because it helps to obtain evaluation results independent of primary images,and that the method is simple in principle,easy in realization and convenient in usage due to the non-engagement of primary images in the evaluation process.