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RE: [Cfrg] Fwd: Hash-Based Key Derivation

"Tom Shrimpton" <teshrim@cs.pdx.edu> Tue, 25 October 2005 21:08 UTC

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From: Tom Shrimpton <teshrim@cs.pdx.edu>
To: "'Blumenthal, Uri'" <uri.blumenthal@intel.com>, cfrg@ietf.org
Subject: RE: [Cfrg] Fwd: Hash-Based Key Derivation
Date: Tue, 25 Oct 2005 14:07:34 -0700
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> Is it proven that hash function output is uniformly distributed?

Proven?  No, except of course in the random oracle model :)
You might like to look at Bellare and Kohno's paper "Hash Function Balance
and it's Impact on Birthday Attacks."


> Are most cryptographers OK with modelling hash functions as 
> random oracles?

For the purpose of proofs, (sometimes) yes, but not in practice.
The problem is that all of our existing hash functions are based on the 
Merkle-Damgard paradigm, but plain MD doesn't preserve random-oracle-ness.
There's a nice new paper by Coron, Dodis, Malinaud and Puniya 
"Merkle-Damgard Revisited: How to Construct a Hash Function" that addresses 
this issue.

-Tom


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