# Introduction to Hash Functions

From The ECRYPT Hash Function Website

Revision as of 17:27, 10 March 2008 by Crechberger (talk | contribs)

### Security Requirements

The security properties that hash functions are expected to provide, are summarized in the following three basic requirements:

- **Collision resistance**: it is infeasible in practice to find two messages m and m^* != m such that h(m) = h(m^*).

- **Second preimage resistance**: for a given message m, it is infeasible in practice to find a second message m^* != m such that h(m) = h(m^*).

- **Preimage resistance**: it is infeasible in practice to find, for a given hash value y, a message m such that h(m) = y.

In practice there are several other requirements, but for sake of simplicity we stick to them.