Cryptanalysis Of Hash Function HAS-160 And MD5 Potential Danger

Hash functions was not used in cryptography until the end of 1970's.From that moment Hash functions become the very important part in cryptography .Today hash functions play a fundamental role in modern cryptography ,for example in their use for data integrity, message authentication, digital signature scheme, distribution scheme, key exchange scheme, etc. So people put theirs eyes on the hash functions' security.Professor xiaoyun wang developed powerful techniques for analyzing currently popular hash functions in [l][2][3][4][5].They was called modular differential attack and message modification . So the cryptanalysis of hash functions is hot in the cryptography world. Many papers were published recently. Some of them are talking about how to use modular differential attack the other hash functions, and the others are talking about that some schemes are still safe or not after the broken of MD5 etc. hash function.There are three chapters in this paper. In the first chapter, the conception properties and iteration structure of hash functions are introduced, and three important hash functions are also introduced.In the second chapter, birthday attack and modular differential attack are discussed in detail. We also introduced how to break MD5 in [1].In the third chapter, we talk about some potential dangers for hash functions, give a method to find Collisions of MD5 with Any Two IVs. We first introduce the method of Professor xiaoyun wang to attack the problem . It is to combine the method of birthday attack and modular differential attack to decrease the complexity of it .And we give a new method. First, we can use birthday attack to make the output difference of two messages with random initial values satisfy the conditions: Δa= Δb=Δc=Δd,or ,Δa=0, Δb=Δc=Δd, then we can use modular differential attack to find several near-collisions to make the ultimate output difference be zero step by step. When we search for near-collisions, we must use single-message modifications and multi-message modifications to fulfill most conditions.