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Re: [kitten] Finding Kerberos Realm Descriptors in secure DNS

Watson Ladd <watsonbladd@gmail.com> Wed, 16 September 2015 15:11 UTC

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Date: Wed, 16 Sep 2015 11:11:16 -0400
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From: Watson Ladd <watsonbladd@gmail.com>
To: mrex@sap.com
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Cc: kitten@ietf.org
Subject: Re: [kitten] Finding Kerberos Realm Descriptors in secure DNS
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On Sep 16, 2015 10:43 AM, "Martin Rex" <mrex@sap.com> wrote:
>
> Greg Hudson wrote:
> > On 09/15/2015 03:09 AM, Rick van Rein wrote:
> >>
> >> So... it may be reasonable to assume that any KREALM client could
> >> work with multiple realms, because they will normally be KDCs.
> >> And that'd mean we wouldn't need this priority or go-for-this-one flag.
> >> Agreed?
> >
> > A KDC can only return one referral, so I'm not sure what it would do
> > with multiple realms, with or without priorities.  Perhaps I'm missing
> > something.
>
> KDCs and client may have substantially different requirements/purposes.
>
> With traditional Kerberos, a service can only have one unique
> Kerberos principal name (in exactly one Kerberos Realm).
>
> So for users from different locations, which locally authenticate
> via Kerberos, accessing a central (cross-location or cross-organization)
> service traditionally requires Kerberos realm to trust each other
> and transparent cross-location / cross-organization access for some
> very dangerous network protocols.
>
> (dns: upd/53, ldap: udp/389, kerberos: udp/88 and tcp/88)

And these are dangerous because what? Certainly Kerberos is ment to deal
with untrusted hostile things on the network.

>
> Conceptually, setting up a central service with seperate/distinct
> service principals from each remote location/organization totally
> obviates creating long-distance kerberos realm trust relationships
> along with the dangerous network protocols.

This is not a good idea. Suppose I have users with multiple principals from
different realms and server principals from different realms. How do I know
what the access policy applied actually is? That's the advantage of cross
realm trust, if I understand it correctly.

>
>
> In our own Single Sign-On solution, with our own implementation of the
> relevant server-side AP_REQ processing we currently support the concurrent
> use of kerberos service principals from seperate/independent Kerberos
Realms,
> and it is actively being used by customers.
>
>
> -Martin
>
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