Subject: [mobile-ip] Issue 49 (rfc 3041 or new prefixes and manual SAs)

From: Jari Arkko <[email-masked]>
Date: Fri, 28 Jun 2002 00:32:00 +0300

Hi,

I'm trying to write the text relating to solution #2 in this
issue, i.e. to describe the limitations. In doing so have
run into a new problem. (Or perhaps it's just too late evening...)

I'm not sure I see how this works even when automatic keying
is used.

Normally, IKE-based SAs work well even if you change addresses.
However, in this particular application we have the additional
problem that we have to keep track of which SAs are
allowed to send BUs regarding which IP addresses. A naive way
to organize automatic keying is to setup one CA who signs everyone's
certs and then anyone who can present the right kind of cert
gets in and gets a new SA. This SA will have selectors that correspond
to the particular IP addresses from whereever the IKE connection
came from.

However, with this setup any other legal mobile node could claim
they are the node that has my home address, get an SA, and send
an authenticated BU.

So it seems that whatever we do, the certs have to have IP addresses
that tie them to a specific address. Alternatively there has to be
specific SPD entries for each mobile node in the HA. But if we use
either of these two schemes, it's not going to be easy to change
the address.

Essentially, this prevents RFC 3041 home addresses or new prefix
assignment without manual intervention.

Any ideas?

Jari

---

From: Jari Arkko <[email-masked]>
Date: Sat, 29 Jun 2002 01:22:51 +0300

And more issues to close...

I've had a discussion about this issue with a couple of people.
The general feeling seems to be that making mobility work with
privacy in a seamless and secure way may not be achievable
right now. Or rather, it shouldn't be a requirement for the
first version of the MIPv6 RFC.

Let me highlight some of the issues involved in this:

* On manually keyed IPsec SAs we have the problem of binding
   the SAs to the IP addresses, leading to a need for manual
   intervention when addresses change.

* Security schemes that are not directly bound to addresses
   could also be used. But even these schemes have to deal
   with a few non-trivial questions, such as who has the
   authority to send a BU for a specific address to the HA?
   The very first authenticated MN to come up with that address?
   But then we'd have to store all addresses that have ever
   been used. Or perhaps we could allow the address to be
   used if no one else has a binding for it at the moment, or
   DAD succeeds? But what if I hijack everyone else's addresses
   after the HA reboots?

* On certificate-based IPsec, one can use addresses in the
   Subject AltName field to force the HA to allow only the
   given address for the owner of that certificate. This
   would minimize configuration at the HA, but would bind
   every MN to their given addresses.

* For renumbering, it is conceivable that the HA/CA
   could make new certificates for the same MN/public key
   but with the new address. But isn't clear how these
   are pushed to the MNs in the easiest manner.

* For RFC 3041, the problem is harder because the MN
   has the initiative. Perhaps the MN could request
   a new SA/cert using its old address/SA/cert.

Solving all of the above may not be possible in the immediate
future and definately not before Monday 9 AM.

So, I have the following proposal:

- We keep on allowing RFC 3041 home addresses and new prefixes.
- We point out that in order to use these, one must have e.g.
   manually configured SAs suitable for the new addresses.
- We point out that future specifications will deal with this
   problem in a more complete manner.

Does this work for everyone?

Jari