Md5 And Some New Hash Function Analysis

With the development of the computer network and e-commerce, requirements for process of information exchange become more and more urgent. During the course of transmission, the information may be threated or attacked in the form of altered, imitation and denial. All these belongs to the integrity and truth of the information. In order to resolve these problems, we mainly apply the technology of hash function to make sure that the information is integral and not changed.Hash can be called"ha xi"or"san lie"and it is used in digital signature and file checksum. There are many hash functions and MD5 is used more widely than other functions. In 1991, MD5 is invented by professor Ron Rivest of Massachusetts Institute of Technology. And it is developed from MD4. The input message of MD5 is any length, and output is 128 bits. 512 bits can be processed every time which is a input block. It started the research upsurge of MD5 that the successful attack to MD5 by professor Xiaoyun Wang in 2004. In 2008, Doctor Tao Xie designed two differential paths and according to the differential path he found collosion message. These results proved that MD5 is no longer safe and new hash function should be designed. With these reasons, NIST levied new hash function standard SHA-3 in the range of the world. So far, there is only one work left which is to screening SHA-3 from five functions. They are Blake, Gr?stl, JH, Keccak and Skein. Among these functions, the design of Gr?stl is similar to AES. So those methods which are used to analyze AES can be applied to study Gr?stl. In order to pursuit the study of cryptography and do our contributions to the national information safety, we have done the works as following:(1)We successfully designed a new 1-bit differential path through studying the method of differential analysis which is used by Professor Xiaoyun Wang to attack MD5 and the 1-bit differential path designed by Doctor Tao Xie. And we also give the sufficient conditons that the iteration variables need to adopt.(2)We modify the message to make sure that all iteration variables can satisfy the sufficient conditions using the methods such as the modification of muti-message,tunnel ideology and saving the Zhao by besieging the capital of the Wei.(3)The structure of the whole program is determined by the technique of divide-and-conque.(4)For the function Gr?stl, we analyze the differential path of five rounds, six rounds and seven rounds by studying the way of rebound attack. On the base of match-in-the-middele, we give a new eight rounds differential path. Although these attacks can not be realized, it can help us a lot to search the other hash functions which have similar structure in the future.