一种图像加密算法的密码学分析

Cryptanalysis on an Image Encryption Scheme

针对一种基于Cat映射和Lu混沌映射的图像加密方案进行密码学分析,提出三种不同的密码学攻击,即选择密文攻击,选择明文攻击和已知明文攻击。该加密方案利用Cat映射实现像素置乱,并将像素置乱后的矩阵与Lu混沌映射产生的随机矩阵进行异或运算实现图像灰度值的改变。由于该算法存在与密钥等价的等价密钥矩阵,即只要破解出等价密钥矩阵就可以恢复由该算法加密的加密图像,且等价密钥矩阵不随明文图像的改变而改变,使其难以抵抗各种攻击。仿真实验实现了对该算法的三种密码学攻击。

An image encryption scheme based on cat map and Lu chaotic map was proposed recently,where the cat map was utilized to shuffle the pixel positions of the plain- image and the Lu chaotic map was adopted to generate pseudo- random sequences to change the pixels gray values of the shuffled image by bitwise XOR operation. In this paper,we give three kinds of cryptanalysis on this image encryption scheme,including chosen ciphertext attack,chosen plaintext attack and known plaintext attack. In the proposed scheme,the cipher- image is independent on the plain- image and there exists a secret matrix equivalent to the secret parameters. We break the proposed encryption scheme by finding the equivalent secret matrix theoretically. Simulation experiments realize the three kinds of attacks as well.