Subject: Re: Comments on Larry's SPNEGO draft

From: Sam Hartman <[email-masked]>
Date: Mon, 08 Nov 2004 14:34:47 -0500

>>>>> "Ken" == Ken Raeburn <[email-masked]> writes:

    >>> What convincing problem do you have with MAY?
    >>  The following argument should justify a SHOULD (or even a
    >> MUST).
    >> 
    >> "The optimistic token SHOULD always be provided. This is
    >> because if you do not use the optimistic token, and
    >> gss_init_sec_context fails with a continue-able/non-fatal error
    >> after the two sides already agree upon a common mech, we can
    >> not renegotiate the next best available mechanism.  That is not
    >> acceptable."

    Ken> So even if generating the token for the preferred mech is an
    Ken> expensive operation or involves prompting the user for input,
    Ken> and is known only to be supported by a couple of servers out
    Ken> of the dozens that the client will use, you think the token
    Ken> should be generated before negotiating whether the mech will
    Ken> be used?

Yes absolutely.  You need to generate a initial token for any
mechanism you offer to guarantee that you can actually do so.

--Sam

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From: Martin Rex <[email-masked]>
Date: Mon, 8 Nov 2004 21:21:55 +0100 (MET)

> mechanism you offer to guarantee that you can actually do so.

I do not agree.

Although it might be a good in many environments if SPNEGO would check
each mechanism for credentials availability (i.e. gss_acquire_cred)
before listing it in the mechanism list, I don't think that it is
(or should be) a general requirement.

I don't think that doing the initial gss_init_sec_context() for every
mechanism in advance is a good idea.

There are too many "mechanisms" in widespread use that require entry
of either a longterm secret or a passphrase which protects the longterm
secret, and I think none of those should query the user for a secret
unless there is a high probability it is actually required for
succeeding.  The majority of authentication systems currently in use
is still password-based, unfortunately.

-Martin

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From: Sam Hartman <[email-masked]>
Date: Mon, 08 Nov 2004 15:32:18 -0500

>>>>> "Martin" == Martin Rex <[email-masked]> writes:

    Martin> I don't think that doing the initial
    Martin> gss_init_sec_context() for every mechanism in advance is a
    Martin> good idea.

Then we need to do something more complex.  For Kerberos you really
need to do the init_sec_ctx because until you do that you don't know
if the target has credentials.

BTW, are you going to be on jabber for this meeting? ([email-masked])