Paper 2004/253

Design Principles for Iterated Hash Functions

Stefan Lucks

Abstract

This paper deals with the security of iterated hash functions against generic attacks, such as, e.g., Joux' multicollision attacks from Crypto 04. The core idea is to increase the size of the internal state of an n-bit hash function to w > n bit. Variations of this core idea allow the use of a compression function with n output bits, even if the compression function itself is based on a block cipher. In a formal model, it is shown that these modifications quantifiably improve the security of iterated hash functions against generic attacks.