Subject: Re: [MOBILE-IP] challenge / response; MN auth timeout

From: "Karim El-Malki (ERA)" <[email-masked]>
Date: Tue, 25 Jan 2000 19:04:31 +0100

Hi Yoshi

>   But, there is a new problem to this solution:
>   If an MN receives an SA lifetime, the MN must keep the SA
>  until the lifetime
>   is expired.  This means in some cases an MN must keep too
>  many SAs.  If an MN
>   visits many subnets, and if their SA lifetimes are long,
>  SAs to be kept will
>   soon grow more than an MN's ability.

The MN does not necessarily keep an MN-FA SA if it leaves the
relative FA. My understanding is that normally the MN keeps one
MN-FA SA unless it has simultaneous bindings (COAs) at the HA.

>   I will appreciate, if there is a method about re-getting or
>  re-newing
>   keying information with its lifetime.  If there is such a
>  method, an MN can
>   abandon some old SAs before being expired.  Winthout such a
>  method, if an
>   MN abandons an SA between the MN and an FA, an MN cannot
>  anymore register the
>   FA whose SA the MN had abandon before, because the FA knows
>  there is an SA
>   between the FA and the MN.

Are you considering the case in which an MN returns to an FA which
has maintained the MN-FA SA even though it no longer has a binding for
the MN? (unless there are simultaneous bindings)
Can an FA maintain SAs for some time after the expiry of the
relative binding (reg. lifetime)? If so the MN should be aware of
this time period and cache SAs. Anyone have any comments?

Regards,
Karim

---

From: Yoshiyuki Tsuda <[email-masked]>
Date: Wed, 26 Jan 2000 14:56:45 +0900

Hello, Pat and Karim,

 My comments are embedded in the followings:

On Tue, 25 Jan 2000 07:09:07 -0800,  Patrice Calhoun wrote:
>>
>> Yes, the fact that the Mobile Node can simply request new keying material
>> by including the MN-AAA Authentication Extension in the Registration
>> Request. This needs to be supported since we do not know that a Mobile Node
>> no longer has an SA because of laziness, or due to a host reboot.
>>
>> PatC

 Thanks Pat; I'm happy to hear the above.

 You know, according to rfc2002 and rfc2002bis in the 3.7.2.1 section,
 if an FA and an MN share an SA, and if the Mobile-Foreign authentication
 extension doesn't exist in a request, the FA will silently discard the
 request.  And, I couldn't find any related descriptions in the challenge
 draft and an expired keying draft.  So, I assumed an FA would discard
 such a request.
 I'm looking forward to seeing something like the above in a coming keying
 draft.

>> MN-FA SA unless it has simultaneous bindings (COAs) at the HA.

 As for binding information, you are right.  But, as for SAs,
 I don't think so according to the current drafts.

>> this time period and cache SAs. Anyone have any comments?

 Yes, I was saying about this.  From my understanding, an FA will
 maintain SAs for their lifetimes, even if there are no binding.  An
 MN will try to cache SAs.  In case of current laptop PCs, it may be
 OK, because there are plenty of memory and hard disk.  But, in case
 of poor MNs, resources may be restricted, I'm afraid.

 But, Pat mentioned about requesting new keying material.  This will
 enable an MN to discard old SAs before their lifetimes.

Thanks.
-Yoshi

---

From: "Charles E. Perkins" <[email-masked]>
Date: Thu, 27 Jan 2000 13:28:54 -0800

Hello folks,

Excuse my late reply, but I wanted to raise a little more discussion
about the lifetime for the keys generated for the mobile node during
registration.

I think there are two cases.

Clearly, the key generated for use between the mobile node and the
home agent has to have a lifetime.  The key could be used for quite
a few registrations, and should not have to be regenerated every
time the mobile node moves to a new foreign agent.

However, I do not think the same considerations apply for a key
generated for use between the mobile node and the foreign agent.

For instance, I would say that the same key should be used by the
mobile node for as long as it stays at the same foreign agent.
New registrations at the same foreign agent should be able to
use the same key; since the home agent verifies each registration,
and especially if the home agent has a security association with
the foreign agent, there is no need to distrust the mobile node.
And, unless the key is use for bulk data encryption, there is so
little traffic that cryptanalysis is unlikely to succeed in
compromising the key.

Bottom line:
- I think the key generated between mobile node and home agent
  should have a lifetime.  This lifetime _may_ correspond to the
  amount of time that the AAAF is willing to "trust" the home agent.
- I think the key generated between the mobile node and the
  foreign agent should last until the mobile node moves to a
  new care-of address and carries out the protocol operations
  for a smooth handover.

This is the philosophy that is currently reflected in the newly
revised AAA keys draft, which is finally done.

Regards,
Charlie P.