一种图像加密算法的密码分析及其改进  

Cryptanalysis and Improvement of an Image Encryption Scheme

作　　者：叶瑞松[1] 马俊明[1] 曾少君[1] 

机构地区：[1]汕头大学数学系,广东汕头515063

出　　处：《汕头大学学报（自然科学版）》2015年第4期57-70,共14页Journal of Shantou University：Natural Science Edition

基　　金：国家自然科学基金资助项目(11271238)

摘　　要：本文通过对Eslamin和Bakhshandeh所提出的一种改进的基于全局置乱的图像加密算法进行密码分析,发现了该算法不能抵御选择明文攻击.通过选择明文攻击,动态加密选择明文图像,可以将明文图像的像素灰度值逐一恢复,最终得到完整的明文图像信息,成功破译了该算法.针对原加密算法的安全缺陷,笔者对该算法进行了改进.一个改进是设计置换过程的密钥流与明文图像内容相关,克服了原加密算法置换过程与明文图像无关的缺陷,从而可以抵御选择明文攻击、已知明文攻击.另一个改进是在扩散过程采用另一个斜帐篷映射生成密钥流,扩大了加密算法的密钥空间,使得加密算法更加安全.本文还对改进的加密算法的安全性进行了详细的实验分析,包括密钥空间分析、密钥敏感性分析、统计分析、信息熵分析、差分攻击分析等.数值实验结果表明,本文提出的改进的图像加密算法比原加密算法更加安全有效.In this paper, cryptanalysis and improvement over an image encryption scheme based total shuffling proposed by Eslamin and Bakhshandeh are performed. Chosen-plaintext attack is adopted to break the image encryption scheme. Special chosen-plaintext images are constructed to implement the cryptanalysis. The pixel values of plain-image can be recovered one by one from the cipher-image. Therefore the algorithm is vulnerable to chosen-plaintext attack. Two improvements are made to overcome the flaws of the image encryption scheme analyzed. One improvement is to design a plain-image dependent permutation stage to resist chosen-plaintext attack and known-plaintext attack. To enhance the security, another skew tent map in the diffusion stage is employed to obtain larger key space as another improvement. Security analyses including key sensitivity analysis, key space analysis, statistical analysis, differential analysis and information entropy analysis are performed. Compared to the original algorithm, all the experimental results demonstrate that the proposed image encryption scheme shows better security and effectiveness.

关 键 词：混沌系统 选择明文攻击 置换 扩散 图像加密 密码学分析 

分 类 号：TP391[自动化与计算机技术—计算机应用技术]