Subject: Re: Using TLS with Kerberos 5

From: Jeffrey Hutzelman <[email-masked]>
Date: Fri, 03 Dec 2004 18:53:21 -0500

On Thursday, November 11, 2004 01:06:53 +0100 Simon Josefsson 
<[email-masked]> wrote:

> Here is a description of a protocol extension I'm using.  If people
> are interested in seeing this pursued within IETF, let me know.  For
> more information, see <http://josefsson.org/krb5starttls/>.

I've not done a detailed review of this document, so I'm not going to
comment on whether your use of TLS fits well with the Kerberos protocol
or on any potential security issues.  However, in my role as Kerberos
WG chair I need to point out a couple of things...

- Rather than simply formatting your document as an internet-draft, you
  should actually submit it to [email-masked] so it can be
  published in the I-D repository.  Anyone can submit an internet-draft,
  even if it does not relate to work currently being done in the IETF.

- I don't believe anyone has previously expressed an interest in working
  on something like this in the IETF.  I do think this falls within the
  scope of krb-wg's charter, if we want to take on the work.  I would
  like to see some discussion as to whether people think this is a good
  idea, and as to whether people are interested in doing this work in
  the IETF.

- Your document defines an extension mechansim which relies on assigning
  special meaning to the reserved high-order bit in the length field
  which precedes each request and response when Kerberos is run over TCP
  transport (see draft-ietf-krb-wg-kerberos-clarifications-07.txt,
  section 7.2.2).  This is a problem.

  According to the specification, this bit is reserved for future
  expansion of the protocol and MUST be set to zero by all compliant
  implementations.  Further, a KDC which sees a nonzero value here
  MUST return KRB_ERR_FIELD_TOOLONG and close the stream.

  In the context of an IETF standards-track specification such as
  Kerberos, a field or value labelled as "reserved" are intended for
  potential use in future versions of the standard, and are _not_
  available for non-IETF extensions.  Please be aware that any
  implementation which treats this bit other than as described in
  the Kerberos specification may fail to interoperate with compliant
  implementations of future versions of Kerberos.

-- Jeffrey T. Hutzelman (N3NHS) <[email-masked]>
   Chair, IETF Kerberos Working Group
   Carnegie Mellon University - Pittsburgh, PA

---

From: "Matt Hur" <[email-masked]>
Date: Mon, 6 Dec 2004 10:46:58 -0800

Simon,
I have not read your document, but I have attached some related work.
There is RFC 2712.  There was also a draft to update 2712, but we let
the draft expire.

-----Original Message-----
From: [email-masked]
[mailto:[email-masked]] On Behalf Of Simon
Josefsson
Sent: Wednesday, November 10, 2004 4:07 PM
To: [email-masked]
Subject: Using TLS with Kerberos 5

Here is a description of a protocol extension I'm using.  If people are
interested in seeing this pursued within IETF, let me know.  For more
information, see <http://josefsson.org/krb5starttls/>.

Thanks,
Simon