Paper 2010/524

Combining properties of cryptographic hash functions

Michal Rjaško

Abstract

A ``strong'' cryptographic hash function suitable for practical applications should simultaneously satisfy many security properties, like pseudo-randomness, collision resistance and unforgeability. This paper shows how to combine two hash function families each satisfying different security property into one hash function family, which satisfies both properties. In particular, given two hash function families $H_1$ and $H_2$, where $H_1$ is pseudo-random and $H_2$ is collision resistant, we construct a combiner which satisfies pseudo-randomness and collision resistance. We also present a combiner for collision resistance and everywhere preimage resistance. When designing a new hash function family for some particular application, we can use such combiners with existing primitives and thus combine a hash function family satisfying all needed properties.