Subject: RE: [mobile-ip] Dynamic Home Agent Address Discovery mechanism

From: "Hesham Soliman (ERA)" <[email-masked]>
Date: Thu, 19 Jul 2001 15:58:21 +0200

> As Mobile IPv6 defines its own built-in security mechanism (please see
> the Binding Update format of the last version of the draft - section
> 5.1), we do not have to use IPsec but, in the same way, the ICMP Home
> Agent address Discovery Request message could embed some own specific
> security mechanism.
> 
	=> I believe IPsec is needed and will work for the HA. 
	 The problems highlighted for MIPv6 / IPsec are not really
	applicable for the HA. In particular the key exchange mechanism.
	This can be preconfigured in the MN. Strong authentication 
	to the HA should be supprted IMHO. 

	Hesham

---

From: [email-masked]
Date: Thu, 19 Jul 2001 13:21:35 -0500

I completely agree with you and am not against the use of IPsec; on the
contrary I agree that IPsec should be possible. 

But it seems that in the last version of the MIPv6  specifiaction, the
authentication data is embedded in the BU; using AH will therefore be
redundant.

To come back to the Home agent discovery, that is true that IPsec with
anycast had not yet been defined, but in that case we do not have to use
IPsec to secure the ICMP Home Agent address discovery messages: as you
said, MN and HA can have a pre-established key they will use for
authentication. Instead of using AH, an authentication data field will
carry the authentication information.

-----Original Message-----
From: ext Hesham Soliman (ERA) [mailto:[email-masked]]
Sent: 19 July, 2001 8:58 AM
To: [email-masked]'
Subject: RE: [mobile-ip] Dynamic Home Agent Address Discovery mechanism 

	Hesham

---

From: "Hesham Soliman (ERA)" <[email-masked]>
Date: Thu, 19 Jul 2001 20:46:06 +0200

> contrary I agree that IPsec should be possible. 
	=> Great !

> authentication data is embedded in the BU; using AH will therefore be
	=> I have NO idea why this was done. I haven't had time to review
	it carefully but I never saw a consensus call on this or any recommendation
	made by the MIPv6 security design team. Even the requirements have 
	not yet been agreed on by the WG.

> carry the authentication information.
	=> You mean define something new in the RS/ RA ?
	Everything is possible but I don't see a benefit here.
	Everyone will certainly know your home prefix, address and 
	you HA's address if they want to. So is it really worth it ?

	Cheers,
	Hesham

---

From: [email-masked]
Date: Thu, 19 Jul 2001 16:14:51 -0500

Hello Hesham,

I completely agree with you on the BU format and for the proposal we
made, some enhancements were suggested in order to improve the Dynamic
Home Agent assignment procedure: the ICMP Home Agent Address Discovery
Request messages were suggested to be optionally authenticated and the
Home Agent Discovery reply messages optionally encrypted.

As described in a previous e-mail, "the reason for authenticating a
Discovery request is to ensure that only valid MNs obtain the list of
HAs serving a subnet or network. Obviously
there are other ways that an attacker can learn about the HAs in a
network, but this approach at least puts in some barriers to having
information about HAs in a network being publicly available (via the
ICMP discovery request). We believe that operators would like to some
extent protect the identity of the HAs in their network. So the
mechanism suggested helps such cases. If a network wants to be open,
then yes you do not need to have the authentication of the discovery
message."

"But as we mentioned, it's an option that needs to be supported in the
spec."

Using the Binding Update messages, "an attacker only learns about a
single HA being used by some user as opposed to getting information
about all HAs in a network via the current ICMP Home Agent address
discovery messages. I guess it's a matter of making it harder for the
attackers to discover information on HAs. Many different kinds of
attacks could be launched targeting HAs in a network and this could be
at least to some extent made harder if the info about HAs was not
readily available.
Only the attackers on the MN-HA paths would be able to get the serving
HA address which reduces the potential number of attackers
significantly."  

Best Regards,

Franck

---

From: "Hesham Soliman (ERA)" <[email-masked]>
Date: Fri, 20 Jul 2001 00:37:25 +0200

Hi Franck, 

> HA address which reduces the potential number of attackers
	=> Understood, but I was wondering whether there is 
	a great advantage in hiding one HA vs many. 
	Anyway, when you talk about your proposal are you 
	referring to the DIAMETER extensions draft ?
	I have some comments on it. I suppose I can send 
	them to the list after the draft deadline. 
	If you're referring to another proposal I'd appreciate a pointer. 

	Regards,
	Hesham

---

From: [email-masked]
Date: Fri, 20 Jul 2001 09:37:46 -0500

If you're referring to another proposal I'd appreciate a
pointer. 

Hello Hesham,

Well the question is "Can you really hide the identity of your HAs?" And
from the current spec, that is not totally possible. But it should also
be made more difficult to obtain the identity of the HAs in a network.
The current discovery mechanism allows just about anyone to send the
ICMP discovery request and obtain a list of all HAs in the network. 
So it really boils down to making it a little more difficult to learn
the identity of HAs.

And again to emphasize, the suggestion is to have security parameters in
the discovery message be optional.

The suggestion above does not have anything to do with the Diameter for
MIPv6 draft. The proposal being discussed here is to include this option
in the MIPv6 spec.

Best Regards,
Franck

---

From: "Hesham Soliman (ERA)" <[email-masked]>
Date: Fri, 20 Jul 2001 18:07:37 +0200

> So it really boils down to making it a little more difficult to learn
	=> I understand your concern and appreciate the aim, but my 
	point is that you will never by able to hide the home subnet's
	prefix. Granted that you can make it more difficult to find all
	the HAs on the link, for a price. Until we see a proposal 
	for securing the HA discovery mechanism it is difficult 
	to know what that price is.

> the discovery message be optional.
	=> Understood, but since IPsec is not really an option here 
	we need to evaluate the method for securing the discovery. 
	That's why I asked if you had a proposal. Simply adding text 
	to say it should be secure is not enough. Perhaps when the final solution 
	comes out for securing BUs we could see if it can be 
	reused.  
	But so far, the solutions proposed for key exchange don't 
	seem to work for an anycast address either, unless I
	missed something.

	Regs,
	Hesham

---

From: Vijay Devarapalli <[email-masked]>
Date: Mon, 23 Jul 2001 13:41:42 -0700

Hesham and Franck,

take a look at threat H.1 in section 6.8 of 
draft-team-mobileip-mipv6-seq-reqts-00.txt 

the requirement H.1 that follows it, states that 

"An HA which responds to an ICMP home agent discovery message
MUST only do so after authenticating the MN's identity".

Vijay