MD5 algorithm has important applications in the field of data encryption such as digital signature, identity authentication and so on, but it can not resist differential attack and dictionary attack. This paper does certain special transform on some related variables during message preprocessing course of MD5 to improve probability of data high overflow, and increase the avalanche effect and difficulty of differential cryptanalysis, so that collision problem of MD5 algorithm is solved. Through doing collision detection, coincidence detection of encrypted values before and after improvement for improved algorithm, the improved MD5 is proved safe and practical.%MD5算法在数字签名、身份认证等数据加密领域有重要的应用,但其无法抵御差分攻击和查字典攻击.为此,通过对算法消息处理过程中涉及的一些变量进行特殊变换,提高运算中数据高位溢出的几率,增强其雪崩效应,增加差分分析的难度,由此解决MD5算法的碰撞问题.对改进的算法进行碰撞检测、加密值重合检测以及改进前后加密值的重合检测,结果证明其具有较高的安全性和实用价值.
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