Re: Ticket and SA lifetime (Re: kink-09)

What I'd appreciate here is some insight as to what other
Kerberized applications do, especially ones that have their
own session timers. If they all mimimize their lifetimes to
the extant of the kerberos ticket lifetime, then that pretty
much tells us we should too. If some are independant, then I
think it's probably a local policy decision of the receiver
assuming that the ISAKMP negotiation allows a longer proposed
lifetime to be shortened by the receiver. If that's the case,
then I don't think that the spec needs to recommend anything,
and if it does it should at most be a SHOULD.

		Mike

Kazunori Miyazawa wrote:
> 
> KAMADA Ken'ichi wrote:
> 
>> At Wed, 7 Sep 2005 15:08:29 -0400,
>> Ken Raeburn <[email protected]> wrote:
>>
>>> Relatively minor stuff:
>>
>>
>>
>>> - Section 3.6: One case that might be worth mentioning is when the  
>>> user's tickets are going to expire at the end of the "hard lifetime  
>>> by time" of the SA.  In that case, unless there's some other reason  
>>> (lifetime by byte count?), there's no purpose in attempting to 
>>> rekey,  because the new SA will have the same expiration time.  (This 
>>> sort of  applies also in renewable-TGT or PKINIT or keytab cases when 
>>> the KDC  isn't available to issue a new TGT, but that could be seen 
>>> as  starting the rekey process and then failing.)  In some 
>>> environments,  it may make sense to prompt the user to re-enter their 
>>> password, but  until the new tickets are actually acquired (or the 
>>> byte count gets  high enough), it makes no sense to continue.
>>
>>
>>
>> Do you assume that the SA lifetime is truncated to the ticket endtime?
>>
>> Is the lifetime of application session limited to the service ticket
>> in usual Kerberized applications?
>> I.e., if I (kerberized-)telnet to a remote host with a service ticket,
>> what will happen when the ticket expires?  Is the telnet session
>> disconnected?
>> # I can't find something on this in RFC 4120 or RFC 2942.
>>
>>
>> Sidenote: at least when Key Exchange payloads are used,
>> a ticket and an SA will have independent lifetimes.
>>
> 
> I think Mr. Raeburn might point that KINK should obtain new ticket 
> before rekey
> if the ticket is going to expire.
> 
> I accordingly thought we needed to change the 2nd paragraph in the 
> section 3.6 to
> 
>    There are no special semantics for rekeying SAs in KINK.  That is, in
>    order to rekey an existing SA, the initiator must CREATE a new SA
>    followed by either deleting the old SA with the DELETE flow or
>    letting it timeout (If the initiator needs a new service ticket
>    it should obtain it in advance).  When identical flow selectors are
>    available on different SAs, KINK implementations SHOULD choose the SA 
> most
>    recently created.  It should be noted that KINK avoids most of the
>    problems of [IKE] rekeying by having a reliable delete mechanism.
> 
> But, I found in the section 3
> 
>    KINK uses Kerberos as the authentication mechanism, therefore a KINK
>    host needs to get a service ticket for each peer before actual key
>    negotiations.  This is basically a pure Kerberos exchange and the
>    actual KDC traffic here is for illustrative purposes only.  In
>    practice, when a principal obtains various tickets is a subject of
>    Kerberos and local policy consideration.
> 
> I think when and how getting a servcice ticket is a local matter and
> it does not cause interoperability issues so that we don't need the change.
>