[CI] Re: Finding collision resistant hash functions

[Major Variola (ret)]

At 11:18 PM 7/7/03 -0700, Sarad AV wrote:
>Lets say we are using SHA-1 and i hash 2^80
>messages.What I am looking for is a compression
>function such that the chances of collision in the
>message digest obtained by hashing these 2^80 messages
>is collision free or very low probability of
>collision.How do we make such a compression function?

You don't need one with a good hash function.

Consider a hash made out of a block cipher digesting
the input.  A block cipher has the property that any
one bit difference in input will change half the output
bits on average.  There's nothing gained by increasing
the input entropy (compressing).