Abstract: The collision attack on MD4 is investigated，a new difference method that local collision does not exist in the third round of the differential path，is proposed.The results show that the new differential path has no sufficient condition in the third round to be satisfied.The efficiency of the collision attack which is using this differential path is superior to that of all known attacks.The complexity is less than 1 MD4 operation，which is smaller than the previous best work.

Key words: Hash function, MD4, message difference, differential path, collision attack

摘要： 在对Hash函数MD4的已知碰撞攻击方法研究的基础上，提出了一个新的分析思路——在差分路径的第3轮中不再构造局部碰撞，并给出了一条全新的差分路径。结果表明：新的差分路径在第3轮中不存在充分条件需要满足，以此路径构造的MD4碰撞攻击效率与以往攻击结果相比最优，计算复杂度不超过1次MD4运算。

关键词: Hash函数, MD4, 消息差分, 差分路径, 碰撞攻击