Subject: Re: Last Call: 'Kerberos Cryptosystem Negotiation Extension' to Proposed Standard

From: Jeffrey Hutzelman <[email-masked]>
Date: Mon, 06 Feb 2006 18:00:06 -0500

On Friday, January 13, 2006 06:12:33 PM -0500 The IESG 
<[email-masked]> wrote:

> The IESG has received a request from the Kerberos WG WG to consider the
> following document:
>
> - 'Kerberos Cryptosystem Negotiation Extension '
>    <draft-zhu-kerb-enctype-nego-04.txt> as a Proposed Standard
>
> The IESG plans to make a decision in the next few weeks, and solicits
> final comments on this action.  Please send any comments to the
> [email-masked] or [email-masked] mailing lists by 2006-01-27.
>
> The file can be obtained via
> http://www.ietf.org/internet-drafts/draft-zhu-kerb-enctype-nego-04.txt

No comments were received during the IETF Last Call for this document.  The 
document was approved by the IESG last week; complete details can be found 
in the I-D tracker at <https://datatracker.ietf.org/public/pidtracker.cgi>.

There were three comments raised during IESG evaluation.  Two of these were 
relatively straightforward, and can/will be handled in an RFC-Editor note. 
The third comment is one I'd like the WG to look at.

Brian Carpenter writes:

> At the end of section 3:
>    The server MAY ignore the preference order indicated by the client.
>    The policy by which the client or the server chooses an enctype
>    (i.e., how the preference order for the supported enctypes is
>    selected) is a local matter.
>
> Would it be useful to observe that this would actually allow
> a local decision to prefer weaker security than chosen by the KDC?

This is a comment, not a discuss, so it doesn't block progress.
However, I'd like to ask the WG to consider Brian's question, and whether
it would be useful to add a sentence to this effect.  Note that no one is 
suggesting a change to the protocol, just adding an observation to the 
text.  If we decide we want to do this, it can be done in an RFC-Editor 
note.  I'd like to come to some conclusion on this by the end of the week.

-- Jeff

---

From: Sam Hartman <[email-masked]>
Date: Mon, 06 Feb 2006 23:10:56 -0500

>>>>> "Jeffrey" == Jeffrey Hutzelman <[email-masked]> writes:

    Jeffrey> There were three comments raised during IESG evaluation.
    Jeffrey> Two of these were relatively straightforward, and
    Jeffrey> can/will be handled in an RFC-Editor note. The third
    Jeffrey> comment is one I'd like the WG to look at.

    Jeffrey> Brian Carpenter writes:

    >> At the end of section 3: The server MAY ignore the preference
    >> order indicated by the client.  The policy by which the client
    >> or the server chooses an enctype (i.e., how the preference
    >> order for the supported enctypes is selected) is a local
    >> matter.
    >> 
    >> Would it be useful to observe that this would actually allow a
    >> local decision to prefer weaker security than chosen by the
    >> KDC?

I don't think this is actually true.  Or at least it is only true if
the client offers enctypes weaker than the KDC session key.  The
client SHOULD NOT do this according to the protocol, so it is rarely
the case that the server can choose a weaker key.

As such I don't think this requires mention.

--Sam

---

From: Jeffrey Hutzelman <[email-masked]>
Date: Tue, 07 Feb 2006 16:15:13 -0500

> As such I don't think this requires mention.

Anyone else?  I said I'd let this go until the end of the week, but if I 
don't hear any further comments by then, we'll move the document forward 
without any changes related to this comment.

-- Jeff

---

From: Nicolas Williams <[email-masked]>
Date: Tue, 7 Feb 2006 15:32:02 -0600

> without any changes related to this comment.

The initiator and acceptor can use this to negotiate a weaker key than
the KDC might have liked, that's true, but it has always been possible
for those parties to ignore the KDC's wishes, particularly now that we
have GSS_Pseudo_random().  As such I don't think this needs to be
mentioned -- it's elementary that after the TGS exchanges the client and
server can shoot their feet off if they want to.

Nico
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