基于变步长约瑟夫遍历和DNA动态编码的图像加密算法的安全性分析

近年来，不断有新的图像加密算法被提出，其安全性却未得到充分的分析和验证。该文对一种最新报道的图像加密算法的安全性进行了分析。所分析算法通过基于变步长约瑟夫遍历的像素置乱、基于DNA动态编码的像素替换及像素行列扩散来完成图像加密。分析表明，该算法的秘密密钥设计不具有实用性，加密过程也存在缺陷。在选择明文攻击条件下，对该算法的加密过程进行了密码分析，并提出了相应的攻击算法。仿真实验和理论分析确认了所提攻击算法的有效性与可行性。最后，针对所分析算法及部分图像加密算法中存在的问题，提出了改进建议。

Cryptanalysis of Image Encryption Algorithm Based on Variable Step Length Josephus Traversing and DNA Dynamic Encoding

In recent years, new image encryption algorithms have been continuously proposed, but their security has not been fully analyzed and verified. The security of a newly reported image encryption algorithm is analyzed in this paper. The analyzed algorithm achieves the image encryption through pixel scrambling based on variable step length Josephus traversing, pixel substitution based on DNA dynamic encoding, and pixel diffusion in row and column directions. Analysis shows that the secret key design of this algorithm is not practical, and its encryption process also has defects. Under the condition of chosen-plaintext attack, the encryption process of this algorithm is cryptanalyzed, and a corresponding attack algorithm is proposed. Simulation experiments and theoretical analysis confirm the effectiveness and feasibility of the proposed attack algorithm. Finally, in view of issues in the analyzed algorithm and some image encryption algorithms, several suggestions for improvement are given.