Subject: [Cfrg] Question on key size reduction for Cipher-based PRFs and MACs

From: "Narayanan, Vidya" <[email-masked]>
Date: Wed, 11 Jul 2007 17:38:12 -0700

Hi,
RFC4615 defines a mechanism to construct a key for AES-CMAC-PRF-128 from
a smaller or bigger key using the following mechanism: 

K := AES-CMAC(0^128, VK, VKlen) 

Can that approach be generalized for all cipher-based PRFs in the
following manner:

K := Cipher-based-PRF(0^block-size, VK, VKlen)? 

If not, what are the issues with doing so and how else could we handle
key size reductions for cipher-based PRFs? 

Also, does this approach equally apply to Cipher-based MACs as well
(i.e., K := Cipher-based-MAC(0^block-size, VK, VKlen))? 

Thanks,
Vidya

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