对一种基于比特置乱的超混沌图像加密算法的选择明文攻击

最近,一种基于比特置乱的超混沌图像加密算法被提出,其核心思想为:首先,用混沌序列对明文图像进行像素置乱操作；然后,根据一个随机序列中相邻两个元素的大小关系对像素进行不同的比特位置乱；最后,把经过比特置乱后的序列与另一个混沌序列进行扩散、混淆运算得到最终的密文图像,从而使明文图像达到更好的加密效果。对该加密算法进行了安全性分析,发现该算法的安全性完全依赖于3个混沌序列,通过选择明文攻击依次破解出原算法中的3个混沌随机序列,恢复出了明文图像。理论分析和实验结果验证了所选择明文攻击策略的可行性,同时对该算法进行了改进,在改进算法中混沌系统的初始值与明文图像的SHA-256哈希值有关,从而使得密钥流与明文图像相关,因此算法可以抵抗选择明文的攻击。

Chosen Plaintext Attack on Image Encryption Algorithm Based on Bit Scrambling and Hyperchaos

Recently,an image encryption algorithm based on bit scrambling and hyperchaos was proposed,whose main idea is as follows.First,a chaotic sequence is used to scramble pixel values of plaintext image.Then,according to the size of two adjacent elements in a random sequence,internal bit of each pixel is scrambled.In the end,the final ciphertext image is obtained by the diffusion and confusion of the scrambling sequence,and chaotic sequence,and plain image information can be well hidden.In this paper,the security of the above encryption algorithm were analyzed.It is found that the security of the algorithm depends entirely on three chaotic sequences by choosing plaintext attack.The three chaotic random sequences in the original algorithm were obtained,thus the plaintext image was restored.Theoretical analysis and experimental results verify the feasibility of the chosen plaintext attack strategy.At the same time,the improved method was given.In the improved algorithm,the initial value of the chaotic system is related to the SHA-256 hash value of the plaintext image,so that the key stream is related to the plaintext image.Then the algorithm is resis-tant to the attack of chosen plaintext.