对一维复合混沌图像加密算法的安全分析和改进

最近，Park 等人提出了一种基于一维复合混沌的图像加密算法，该算法的核心思想为：用混沌序列对明文图像进行像素置乱操作；利用混沌序列和密文反馈机制对置乱后的明文序列进行扩散操作；把扩散后的密文序列向左循环移位以得到最终的密文。对该加密算法进行了安全性分析，发现了该算法的两个等效密钥流，从而使得循坏移位操作成为无效操作。通过选择明文攻击依次破解出算法中的两个等效密钥流，恢复出了明文图像。理论分析和实验结果验证了选择明文攻击策略的可行性；此外提出了一种改进算法，克服了原有算法的缺陷。改进后的方案不仅能保持原算法的优点，还能抵抗选择明文的攻击。

Cryptanalysis and enhancements of image encryption algorithm based on combination of 1D chaotic map

Recently, Park et al proposed a image encryption algorithm using combination of the 1D chaotic map, the main idea of the encryption algorithm is as follows. First, a chaotic sequence was used to scramble pixel values of plaintext image. Secondly, the chaotic sequence and the ciphertext feedback mechanism are used to diffuse the sequence of the plaintext after the scramble. Finally, the diffused of the ciphertext sequence is shifted to the left to get the final ciphertext. In this paper, we carry out the security analysis of the encryption algorithm, and find the two equivalent key streams of the algorithm, which makes the shift shift operation a invalid operation. By selecting the plaintext attack, we break the two equivalent key streams in the algorithm in turn, so we can restore the plaintext image. Theoretical analysis and experimental results verify the feasibility of the chosen plaintext attack strategy. In addition, we propose an improved algorithm to overcome the defects in the above original algorithm. Experimental results show that the improved scheme can not only maintain the merits of the original one, but also resist the attacks