Overview of hash functions

Abstract

In this chapter we reviewed the basic definitions of hash functions. We presented several classifications for hash functions. The first classification divides the proposed hashed functions according to their level of security. In this classification they are divided into weak and strong one-way hash functions. The second classification was more concerned with the technical issue of whether a private key was involved in the scheme or not. The third classification was concerned with the structure of the hashing algorithm itself, and it considered whether a block cipher had been applied as the underlying one-way function. We reviewed various proposals, and divided them according to the third classification.

Although this chapter does not cover all the proposals, whether based on a block cipher or on other one-way functions, it gives a representative overview of the type of proposals and the problems associated with them. At the end, we remark that our aim is to develop some design rules for the construction of hash functions where they are considered as block-cipher-based and non block-cipher-based.