Do multiple token exchanges ever happen?

Shawn M Emery Shawn.Emery at
Thu Dec 17 16:26:00 EST 2009

Nicolas Williams wrote:
> On Thu, Dec 17, 2009 at 03:49:01PM -0500, Greg Hudson wrote:
>> On Thu, 2009-12-17 at 15:27 -0500, Matthew M. DeLoera wrote:
>>> I do recall seeing it when playing around with NTLM and SSPI once upon a 
>>> time. How about with Kerberos-only?
>> It may happen with SPNEGO and krb5, though I'm not certain.
>> It can definitely happen with IAKERB and krb5, but that feature won't be
>> in MIT krb5 until 1.9.
>> For a basic krb5 exchange, I believe gss_init_sec_context will return
>> GSS_S_CONTINUE_NEEDED for mutual authentication, but that's still only
>> one token exchange from each side.
> One could also see it happening with user-to-user auth.

In Windows using SPNEGO; continue needed is used in cases when acceptors 
send error tokens (viz Kerberos) back to initiators.  The security 
context should be preserved by the application, with the expectation 
that a second request is sent by the initiator w/o encapsulating the GSS 


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