Re: [kitten] I-D Action: draft-ietf-kitten-pkinit-freshness-01.txt

Benjamin Kaduk <kaduk@MIT.EDU> Wed, 29 April 2015 20:25 UTC

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Date: Wed, 29 Apr 2015 16:25:00 -0400 (EDT)
From: Benjamin Kaduk <kaduk@MIT.EDU>
To: Michiko Short <michikos@microsoft.com>
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Cc: "kitten@ietf.org" <kitten@ietf.org>, Sam Hartman <hartmans-ietf@MIT.EDU>
Subject: Re: [kitten] I-D Action: draft-ietf-kitten-pkinit-freshness-01.txt
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On Mon, 27 Apr 2015, Michiko Short wrote:

> Time for me to publish a new draft since this one is expiring.
>
> We found a use case in our implementation of PKInit where the client
> must request a freshness token or else they will get a principal not
> found error, so we need to keep the client behavior. I would prefer to
> not make that MS-PKCA Microsoft extension. It there any problem with
> keeping the client language as is? Also we would prefer to keep token
> generation limited to the public key case. Yes, we are hoping to expand
> the number of customers who use PKInit, but there will still be
> customers for a while who do not, have old servers, etc.

I think I've lost track of which client behavior is in question -- is this
just the part where the client sends an empty PA_AS_FRESHNESS padata to
indicate support of freshness tokens and prompt the KDC to send one (in
contrast to having the KDC always send a freshness token on all requests
or all requests being offered PKINIT)?

It does not seem like a bad scheme to me in the abstract, but it seems
that if we permit it, than all clients wishing to use freshness tokens
must be prepared to implement it, in case they encounter a KDC which does
not proactively provide freshness tokens.  That's probably fine, but we
should consciously take that choice instead of just falling into it.

-Ben