Re: [Gen-art] Gen-ART Review of draft-ietf-kitten-pkinit-freshness-07

Benjamin Kaduk <kaduk@mit.edu> Thu, 01 December 2016 02:59 UTC

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Date: Wed, 30 Nov 2016 20:59:12 -0600
From: Benjamin Kaduk <kaduk@mit.edu>
To: "Paul Miller (NT)" <paumil@microsoft.com>
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Cc: Michiko Short <michikos@microsoft.com>, IETF Gen-ART <gen-art@ietf.org>, "draft-ietf-kitten-pkinit-freshness.all@ietf.org" <draft-ietf-kitten-pkinit-freshness.all@ietf.org>
Subject: Re: [Gen-art] Gen-ART Review of draft-ietf-kitten-pkinit-freshness-07
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On Mon, Nov 28, 2016 at 09:53:35PM +0000, Paul Miller (NT) wrote:
> Minimum length is a problematic topic due to the fact that we intentionally did not specify the format of the freshness token.  Since the structure of the freshness token is left up to the KDC, there is no good way to determine a minimum size.  If the freshness token is a nonce then the size is determined by the birthday problem.  If it is based on symmetric cryptography, then there are different length considerations.  If it is based on asymmetric crypto then there is a third set of size considerations.

We could still mention in the security considerations that depending on the
construction of the token, the token should have some minimum size; essentially,
your text from above.

-Ben