Research On Cryptographic Hash Functions

Cryptographic hash functions play a key role in information security, but the research of hash functions is infantile stage with the MD4,MD5,SHA0 broken by Xiaoyun Wang etc. in the year of 2004 and 2005, respectively.In this thesis, we give an overview of the basic concepts of cryptographic hash functions, MACs(message authentication code) ,one-way function and some the most important application of one-way function. We discuss the generic attacks of cryptographic hash function ,the relations of properties of hash functions and the different approaches that are used for the design of cryptographic hash functions, we describe the history of dedicated hash functions(MDx-class) that are all based on similar design ideas and give generic comments on the design and cryptanalysis of this type of hash functions.All known hash functions are based on the iteration of a compression function, and we have explained that a designer can focus his attention on building a secure compression function. For the design of a compression function one can either start from scratch and build a function specific for the purpose of hashing or use existing cryptographic building blocks such as block ciphers.We discuss cryptographic hash functions(MDC-2,MDC-4) based block ciphers and propose a improved 2m-bit iterated hash function (named PMDC-2) based MDC-2, whose efficiency is much better than MDC-2, and analyze the security of this improved scheme.