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

"Tom Shrimpton" <teshrim@cs.pdx.edu> Tue, 25 October 2005 20:58 UTC

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From: Tom Shrimpton <teshrim@cs.pdx.edu>
To: 'Simon Blake-Wilson' <sblakewilson@bcisse.com>, cfrg@ietf.org
Subject: RE: [Cfrg] Fwd: Hash-Based Key Derivation
Date: Tue, 25 Oct 2005 13:58:15 -0700
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> But a PRF also assumes random or pseudorandom, rather than 
> merely unpredictable input, doesn't it?

Actually, a PRF makes no assumptions about the distribution of the inputs,
but it does assume that the key is random and secret.  In some
constructions,
like the one that David suggested F(S,X) = SHA256-HMAC(SHA256(S), X) the key
S
effectively is part of the "input", so maybe this is what you mean?

Cheers,
Tom


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