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

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