Re: hash function

From: Aldar C-F. Chan (aldar_at_comm.utoronto.ca)
Date: 02/21/05 

Date: Mon, 21 Feb 2005 22:03:09 GMT

> In effect, you want F_k(x) = hash(x||a) to be a PRF. Any chance you can
> use a standard PRF instead of a hash-based construction? For instance,
> something like AES-OMAC, SHA1-HMAC, etc.?

I need the hash function be public, so PRF does not fit. If I relax the
requirement
to just keeping x secret (instead of guarding against a collision to x), I
am
wondering if hash(x||a) = E_{f(x)}(a) works (with f(x) being another hash
function).

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