对像素置乱和比特替换混沌图像算法的破解

Breaking a chaotic image encryption algorithm based on pixel scrambling and bit substitution

最近,一种基于像素置乱和比特替换的混沌图像加密算法被提出,该算法的基本思想为:首先,用混沌序列对明文图像进行像素值置乱操作;其次,将置乱后的明文序列嵌入到另外两组混沌序列中;最后对两组各自嵌入一半明文信息的两个混沌序列进行异或运算,即为最终的密文图像。对该加密算法进行了安全性分析,发现整个加密算法的等效密钥就是三个混沌序列,而这三个混沌序列的生成与明文图像或其对应的密文图像没有任何关系的安全漏洞。通过一幅特殊的密文图像与待解密的密文图像的异或运算恢复出了置乱后的明文图像序列,使得比特替换不起作用;最后通过多幅选择明文图像攻击破解了置乱序列,恢复出了明文图像,理论分析和实验结果都验证了该选择明文攻击策略的可行性。

Recently, a chaotic image encryption algorithm based on pixel scrambling and bit substitution was proposed, whose main idea was as follows. First, a chaotic sequence was used to scramble pixel values of the plaintext image. Then, the scrambled plaintext sequence was embedded into the other two chaotic sequences. Finally, the two chaotic sequences embedded with half plaintext information were XOR operated to obtain the ciphertext image. In this paper, the security of the above encryption algorithm was analyzed and it was found that that the equivalent key of the encryption algorithm is three chaotic sequences, which are not related to the plaintext image or its corresponding ciphertext image. The sequence of scrambled plaintext image was obtained through XOR operation of a special cipher image and the encrypted image to be decrypted. Therefore, the bit substitution fails. The scrambled sequence was recovered by chosen plaintext attack and the plaintext image is restored. Theoretical analysis and experimental results verify the feasibility of the chosen plaintext attack strategy.