GSS-API and libkrb5 behavior for Anonymous tickets
hartmans at MIT.EDU
Wed Nov 4 16:13:25 EST 2009
>>>>> "Jeffrey" == Jeffrey Hutzelman <jhutz at cmu.edu> writes:
Jeffrey> --On Tuesday, November 03, 2009 11:41:55 AM -0600 Nicolas
Jeffrey> <Nicolas.Williams at sun.com> wrote:
> Just because the mechanism can do that doesn't mean it should. I'd
>> rather treat the anon req_flag as critical in the mechanism
>> implementations, even though from the application's p.o.v. it's
Jeffrey> Me too.
Jeffrey> Normally, we tell application implementors to check the
Jeffrey> return state and not use a context that doesn't meet the
Jeffrey> application's needs; this allows applications lots of
Jeffrey> flexibility in asking for the moon and using what they
Jeffrey> can get. However, anon_req is qualitatively different
Jeffrey> here, in that if you request an anonymous context,
Jeffrey> complete context establishment, and end up with a
Jeffrey> non-anonymous context, you've given away the farm even if
Jeffrey> you don't use the context. Now, we provide applications
Jeffrey> a way to prevent this by indicating anon_state early
Jeffrey> enough that they can decline to send a token along that
Jeffrey> would reveal the client's identity. But, I'm inclined to
Jeffrey> think it's better (safer) for mechanisms simply not to
Jeffrey> establish a context at all if anonymity is requested and
Jeffrey> cannot be provided.
If you're going to do the work to standardize this behavior, I wouldn't mind much, although I probably would mildly disagree.
However, I disagree fairly strongly unless this is going to be
accompanied by an update to 2743. My argument is that it breaks
conforming GSS-API applications. If I'd prefer anonymous but would be
willing to accept an authenticated context, then I would end up
failing with your mechanism. If I'm writing a portable application I
have to check the output flag anyway, even if some mechanisms do offer
So, with your approach, you complicate the life of every portable application.
That seems poor.
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