The Analysis Of Resistance Of Hash Functions

Analyzing the collision resistance of hash algorithm, especially the MD5 Message Digest Algorithm, utilizing differential cryptanalysis, this project tried to give some advice and prediction on how to improve hash functions.As a hash function, which was widely used in cryptographic world, an iteration of MD5 algorithm includes 4 rounds (each round with 16 steps) and one addition. Through analyses from steps to rounds, from rounds to iterations, the author gave the limitations of recent researches and how to overwhelm them.Differential cryptanalysis was an approach and utility which was very commonly used by cryptanalyst. First reported by Biham and Shamir for DES, differential cryptanalysis was not only the most effective cryptanalysis of block cipher and one-way hash function, but also the most important basis to prove security of cryptosystem. Differential cryptanalysis was used to other cryptosystem, too.Basing on the recent researches in the hash world, the author had done something good to it: 1, Report the differential cryptanalysis and its application in DES cryptanalysis; 2, Ameliorating the conclusions of reference 7; 3, Making the probability analyses of reference 7 confirmable with the conclusion of 2; 4, Giving the biggest probability of k of k-preimage attack of Wang-like collisions; 5, Giving an analysis of the algorithm and quantitative data of reference 8; 6, Adoption of DES differential analysis and comparison with the hash function differential analysis, we get the general approach and the methodology adopted for the systematic analysis of MD5, and implement it in the other hash function like MD4; 7, Wandering on the weak collision resistance of the strong collision of Wang-like analysis, and with the conclusion that it was not applicable to break the MD5 with weak collisions; 8, Giving four directions or advices on how to improve on hash functions at the end of this paper.