Abstract: Based on the security analysis of a simple and sensitive hyperchaotic image encryption algorithm, it finds that the security of the algorithm relies on two random sequences [SP] and [K]（where the generation of [SP] is related to the plaintext image and the sequence [K]）. However, in fact, the security of the original encryption system only depends on the random sequence [K], and the generation of the random sequence [K] depends only on the initial value of the chaotic system and is independent of the image to be encrypted. Therefore, by using chosen plaintext attack, the random sequence [K] is broken out, thus decrypting the target plaintext image. At the same time, the defect that the original algorithm can not resist the active attack is pointed out. Finally, the original algorithm is improved to overcome the shortcomings of the original algorithm. Theoretical analysis and experimental results verify the feasibility of the chosen plaintext attack strategy and the effectiveness of the improved algorithm.

Key words: hyperchaotic image encryption, cryptanalysis, chosen plaintext attack, active attack, SHA-256 Hash value

摘要： 对一种简单、敏感的超混沌图像加密算法进行了安全分析，发现该算法的安全性表面上依赖于两个随机序列[SP]和[K]（其中[SP]的生成与明文图像和序列[K]都相关）。但是，实际上原加密系统的安全性只依赖于随机序列[K]，而随机序列[K]的生成只依赖混沌系统的初始值，与待加密的图像无关。因此，运用选择明文攻击的方法破解出了算法中的随机序列[K]，从而解密出目标明文图像；同时指出原算法不能抵抗主动攻击的缺陷；最后对原算法进行了改进，使其克服了原算法存在的缺陷。理论分析和实验结果验证了该选择明文攻击策略的可行性和改进算法的有效性。

关键词: 超混沌图像加密, 密码分析, 选择明文攻击, 主动攻击, SHA-256哈希值