Abstract: Aiming at the main defect that the present digital image encryption algorithm based on chaotic is difficult to resist the known/choose plaintext attack, this paper proposes an improved algorithm based on cascade chaotic system. Different from traditional Fridrich architecture of confusion and diffusion, an improved encryption algorithm architecture with confusion-diffusion process is proposed, and the original image’s MD5 value is XORed to control cascade chaotic system’s parameters and initial values respectively, increasing the encryption algorithm’s sensitivity of original image, as a result the encryption algorithm can effectively resist known/choice plaintext attack. Experimental results show that the improved algorithm has good encryption efficacy and security, and better results in original image’s sensitivity analysis, can effectively resist known/choose plaintext attack.

Key words: known/choose plaintext attack, cascade chaotic, Message-Digest algorithm 5（MD5）, confusion-diffusion, security

摘要： 针对目前混沌加密数字图像难以抵抗已知/选择明文攻击的主要缺陷，提出了基于级联L-L混沌系统改进的图像加密算法。不同于传统Fridrich置乱和扩散的架构，采用一种新的改进的加密算法架构使置乱-扩散过程相结合，并利用明文MD5值分组异或调制级联混沌系统的参数和初始值，增加算法对明文的敏感性，从而使整个加密算法能有效地抵抗已知/选择明文攻击。实验结果表明：该改进算法有着很好的加密效果和安全性，并在明文敏感性分析方面效果更好，能有效抵抗已知/选择明文攻击。

关键词: 已知/选择明文攻击, 级联混沌, 消息摘要算法第5版（MD5）, 置乱-扩散, 安全性