Recently, an image block encryption algorithm was proposed based on some well-known chaotic maps. The authors claim that the encryption algorithm achieves enough security level and high encryption speed at the same time. In this paper, we give a thorough security analysis on the algorithm from the perspective of modern cryptology and report some critical security defects on the algorithm. Given five chosen plain-images and the corresponding cipher-images, the attacker can obtain an equivalent secret key to successfully decrypt the other cipher-images encrypted with the same secret key. In addition, each security metric adopted in the security evaluation on the algorithm is questioned. The drawn lessons are generally applicable to many other image encryption algorithms.

最近，提出了一种基于一些众所周知的混沌图的图像块加密算法。作者声称该加密算法可同时达到足够的安全级别和较高的加密速度。本文从现代密码学的角度对算法进行了全面的安全性分析，并报告了该算法的一些关键安全缺陷。给定五个选定的普通图像和相应的密码图像，攻击者可以获得等效的密钥，以成功解密使用同一密钥加密的其他密码图像。另外，对算法的安全性评估中采用的每个安全性指标都提出了质疑。汲取的教训通常适用于许多其他图像加密算法。