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

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