Subject: Re: Kerberos WG: draft-brezak-spnego-http-00.txt

From: "Tim Bass" <[email-masked]>
Date: Mon, 1 Oct 2001 10:12:51 -0400

----- Original Message -----
From: "Paul B. Hill" <[email-masked]>
Sent: Tuesday, September 25, 2001 5:20 PM
Subject: RE: Kerberos WG: draft-brezak-spnego-http-00.txt

> Paul Hill asks:  Does the informational draft provide sufficient
> information for other developers to create and interoperable client
>  or server?
>
> <http://www.ietf.org/internet-drafts/draft-brezak-spnego-http-00.txt>
>

Paul,

I spent a few hours with the brezak-spnego draft last week.  I pulled down
the referenced RFCs on HTTP, digest,  GSS-API, etc. and tried to look for
gaping holes or inconsistences.   The complexity of the GSS-APIs combined
with only limited analysis time did not permit a full evaluation; however,
on the surface, it looked like 'the draft'  covered-the-bases on their
implementation
of KV5 over HTTP and provided enough information for vendors to build
interoperable systems.    Granted,  I did not drill down as deeply as
required
in all the specs; the proof is in the implementation (and the stability!).

In a few sidebar discussions, people have voiced some concerns about the
GSS-API and the willinging of the large vendor community to use GSS-AFIs.
Other have voiced concerns that MSIE uses the GSS-API in their SPNEGO
implementation, but will other browsers like Netscape follow?    These
are the flavor of the comments we are hearing on this end.  One of our
clients, BTW, plan to  test   KV5 using  MS SPNEGO  (in the months
ahead) between W2K and "another vendors"  security framework,
in a cross-realm environment.

Other comments we are getting are about SAML and how the future
of SAML 'may-or-may-not' effect the long term viability of this draft.

All the Best, Tim

www.silkroad.com

---

From: "John Brezak" <[email-masked]>
Date: Fri, 5 Oct 2001 16:24:17 -0700

I will be posting an updated I-D that address the HTTP use of SPNEGO
based on some of the questions and comments on the list.

A preview:
- HTTP/SPNEGO as implemented in Win2000 is limited to those mech-types
that complete in 1 or 1.5 round trips - such as Kerberos and NTLM. The
updated draft contains the details.
- The client can preemptively send an Authorization header with a
Negotiate+gssapi-data when it "knows" that a particular server can
accept this Authentication mechanism.
- Fix typos and truncation.

Specifc questions about implementation of SPNEGO will not be addressed
in this Internet-Draft.

-----Original Message-----
From: Nicolas Williams [mailto:[email-masked]] 
Sent: Tuesday, October 02, 2001 12:24 PM
To: [email-masked]
Cc: [email-masked]
Subject: Re: Kerberos WG: draft-brezak-spnego-http-00.txt

On Tue, Oct 02, 2001 at 09:03:18PM +0200, Martin Rex wrote:
> 
> Nicolas Williams wrote:
> > 
> > Questions:
> > 
> >  - Can initiators start an HTTP exchange using GSS/SPNEGO for
> >    authentication, knowing, perhaps from a previous successful
> >    connection, that GSS/SPNEGO is required or preferred?
> 
> Good question!
> 
> For basic-authentication, which uses a cleartext username/password, 
> all Web-Browsers perform automatic replay attacks for successive 
> requests so that an additional roundtrip for authentication is only 
> required on the first access.
> 
> GSS-API mechanisms on the other hand *MUST* implement a replay 
> protection on the authentication, so that a simple "cached replay" by 
> the browser
> *MUST* fail.  But when caching the knowledge that authentication
> is required, inclusion of newly created initial context tokens with
> every successive request would also save a roundtrip per request.

Whoa. The GSS Kerberos mech takes care of (or should take care of)
replays -- I expect the same of others. And I'm not talking about
replaying GSS tokens anyways, I'm talking about skipping the null
authentication http connect when the client knows that the server wants
GSS authentication, thus saving a round-trip.

> > 
> >  - As Martin Rex asked, how are GSS tokens other than the first two
> >    exchanged?
> 
> That is really the most interesting question.

I'd like the MS folk to answer it :)

> It would be a total abuse of SPNEGO if an (arbitrary) number of 
> additional roundtrips would not be supported.

Indeed.

> If actually only one roundtrip is supported, then just sending the 
> optimistic initial context token with no SPNEGO would have just been 
> just as good and so much simpler.

Who's to say that there will never be a mechanism that requires several
roundtrips (IAKERB seems to require 1 1/2 roundtrips...).

[...]

> My original example with IAKERB may have been lame, since IAKERB 
> always requires multiple roundtrips (AFAIK at least on the initial 
> context establishment with a new target).
> 
> > 
> >  - Is there, could there be, or, even, should there be a way for the
> >    acceptor to indicate to the initiator what their GSS name(s) is
> >    (are)?
> > 
> >    I'm thinking that http/fqdn@REALM is too hardwired into this 
> > draft.
> > 
> >    What about web services running on ports other than 80?
> > 
> >    Why not support Kerberos names other than http/fqdn@REALM?
> > 
> >    E.g., http-8000/fqdn@REALM, or http/fqdn/8000@REALM, or
> >    funkyweb/fqdn@REALM?
> > 
> >    Can SPNEGO be used to support such naming? Or is SPNEGO incapable
of
> >    "negotiating" the acceptor's GSS mechanism-specific name(s)?
> 
> 
> NOPE.
> 
> The major drawback about SPNEGO is that there is only a negotiation of

> gssapi mechanisms, and it precludes a common namespace for the 
> mechanisms that are being negotiated.

Well, could this proposal be altered so that the http server can include
a possibly null list of exported GSS mech names it responds to? The
default list should be as the draft suggests.

I don't see how this draft can work well without assuming out-of-band
mechanisms for determining a server's GSS names. Since GSS is a general
security service I don't think that assumption can be silently made.

[...]

> > 
> > Pardon my ignorance of SPNEGO.
> 
> That's ok -- as long as you don't author protocol specs that use (or 
> even require) SPNEGO.

Heh.

> -Martin

Nico
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