Security Analysis Of Function MD5

In recent years new collision attack on hash functions made known to the world. A series of hash functions such as MD4, MD5, RIPMD, HAVAL and SHA-0 have been attacked by Wang et al. using Integer Modular Subtraction Differential Analysis Method. So far, two different 2-block collision differentials, both with 3-bit input differences for MD5, have been found by Wang etc in 2005 and Xie etc in 2008 respectively, and those differentials have been improved later on to generate a collision respectively within around one minute and half an hour on a desktop PC. In this thesis, we discussed our latest research results on the analysis of hash function MD5.In this paper, we list the part set of 1-bit to 3-bit input difference patterns that are possibly qualified to construct a feasible collision differential. A new 1-block collision differential with only 1-MSB input difference is presented with the design of its full differential path. Our main contributions are the following:(1) We introduced how to break MD5, including message modification, the general approach to derive sufficient condition set for collision differential path of MD5. The derived conditions for this collision differential path were not sufficient to guarantee the path to hold. To enlarge the collision set, we increased and modified some conditions(2) Some general and basic principles for differential path design are described. The part set of 1-bit to 3-bit input difference patterns is listed.(3) We derived a 2-block collision differential path of MD5. Although now we can't construct efficient attack algorithm according to this 2-block collision differential path, it shows that the general and basic principles is very effective in attack of hash functions.(4) We showed the weakness in MD structure through which we even could construct some hash value collision examples in the practical application. We also analyzed the advantages and disadvantages of the latest various improvements for constructing hash functions.