Abstract: Based on the structural characteristics of the MD5 algorithm, the authors summarized the key points of deciphering the Hash function MD5: the introduction to the message differential, the control of the differential path and the satisfaction of the sufficient conditions. In the process of deciphering the MD5, three differences and the properties of the non-linear functions were introduced. The extensive form of the signed difference and the affection of the left shift rotation were applied in it. The important technique for attack of the MD5 algorithm, named technique of message modification, was cryptanalyzed in detail with an example. In general, the authors explored the key points of deciphering the MD5 algorithm form both the overall analysis and specific practice.

Key words: Hash function, MD5, attack, message modification

摘要： 针对Hash函数MD5算法的结构特点,从明文差分的引入、差分路径的控制和充分条件的确立等方面系统总结了该算法破译过程的关键技术及其主要步骤。首先介绍了破译过程中应用的三种差分的概念,分析了MD5算法中非线性函数的性质以及符号差分的扩展、循环左移的特点,然后从整体的分析思想和具体的实践方法两方面对破译MD5算法的关键技术进行了探索,以实例详细解析了消息修改技术,对Hash函数的破译进行了进一步的研究和探索。的意义。

关键词: Hash函数, MD5, 破译, 消息修改