Re: [STDS-802-16-MOBILE] [security] Summary of issues and requirements for PKMv2
Hi Jeff, all,
I have some concern with the issue of security for the multimedia broadcast
content. Please keep in mind the following facts:
1. In order to fully utilize the possible macro-diversity effect for
broadcast, we have to ensure that the exact same data is transmitted at the
exact same time from all the BS. It could be that this requirement by itself
rules IP out as the convergence layer suitable for such content.
2. It is desired that the broadcast content will be available to MSS in Idle
mode as well.
Given these two issues, I think we want to make sure that when using the
word 'broadcast', everybody means the same thing.
Yigal
-----Original Message-----
From: owner-stds-802-16-mobile@listserv.ieee.org
[mailto:owner-stds-802-16-mobile@listserv.ieee.org]On Behalf Of Jeff Mandin
Sent: Tuesday, May 25, 2004 5:12 PM
To: STDS-802-16-MOBILE@listserv.ieee.org
Subject: Re: [STDS-802-16-MOBILE] [security] Summary of issues and
requirements for PKMv2
DJ,
Our points of contention here seem to be what belongs inside the MAC and
what doesn't....
1. Preauthentication: As I stated earlier, nothing in the preauth
message exchange affects the MAC state of any entity; and byzantine
message forwarding is not properly the job of the MAC layer.
Accordingly, if we add a primitive to the MAC Layer Management Entity's
external interface, we can easily accomodate preauthentication as well
as other Master Key approaches such as the AAA-Server-based ones that
have been discussed in 802.11i .. ie.
InstallMasterKey(MasterKey, MasterKeyId)
[ This assumes the Key caching mechanism from
http://grouper.ieee.org/groups/802/16/tge/contrib/C80216e-04_46r2.pdf ]
2. Support for Key Management by External Server - I agree with what you
wrote, so I'm not sure I understand your objection. Are you stating
that distribution of MAC-layer keys by an external MBS should in fact an
objective for PKMv2? My point is that if the MBS is to control data
access, then it is by definition doing it at L3 and hence way out of our
scope.
3. "Push" for Multicast TEK - Thanks for the observations. Asymmetric
signature is obviously the better approach, but would seem to
necessitate a CA infrastructure or something similar.
- Jeff
>
> Some thought edited in below.. DJ
>
>
> -----Original Message-----
> *From:* owner-stds-802-16-mobile@LISTSERV.IEEE.ORG
> [mailto:owner-stds-802-16-mobile@LISTSERV.IEEE.ORG] *On Behalf Of
> *Jeff Mandin
> *Sent:* Monday, May 24, 2004 11:33 AM
> *To:* STDS-802-16-MOBILE@LISTSERV.IEEE.ORG
> *Subject:* [STDS-802-16-MOBILE] [security] Summary of issues and
> requirements for PKMv2
>
> To the Security Adhoc group,
>
> [snip]
> 4. It's been considered desirable to support a model where a
> backend server (eg. multimedia broadcast content distribution
> server) is responsbile for key management.
>
> [ I think that the best way to support such a broadcast
> distribution model would be with IP-layer security/key management
> and IP multicasting. Then the MAC layer (ie.BS-to-multiple-SS)
> security/key mgt. would be entirely transparent to the content
> broadcast service.]
>
> I have a problem with defining an IP distribution mechanism since
> it is not layer 2. Certainly a management procedure or recommended
> practice could map IP distibution to a well defined L2
> distributions. However at the least we need to provide a L2
> distribution mechanism within the MAC. We cannot assume IP to be
> present, particularly with the ethernet, 802.1Q and ATM
> convergence sublayers.
>
> [snip]
> 6. The PKM-KeyReq/Key-Rsp is inefficient for distributing TEKs of
> Security Associations that are actually used by multiple SS. ie.
> as things stand now, each individual SS sends a KeyReq and
> receives the key in KeyRsp. A more efficient "push mode" TEK
> distribution is desirable.
>
> For this to be possible, without enabling forgery by members of
> the multicast group, it seems that the 'pushed' key needs to be
> signed with the BS private key, using an asymmetric key digest
> mechanism (RSA? DSA?).
>
> There is a lesser level improvement, which is BS initiated key
> transfer. This allows the BS to preempt the key transfer time and
> spread the load of key transfers.
>
> [snip]
> 8. Support for Pre-authentication is desirable - ie. enabling an
> SS to authenticate with a potential target BS via the backbone
> (and establish a shared Master Key) before doing the HO.
>
> [Preauth is an important feature, and can coexist with schemes
> that receive freshly-derived Master Key material from a trusted
> peer BS or ASA server.. However there seems to be no particular
> motivation for running preauthentication inside the MAC - instead:
> preauthentication via a higher-layer mechanism (eg. PANA) using
> the ordinary packet transport is appropriate. Note also that
> running preauthentication inside MAC mgt messages leads to clumsy
> multiple-step proxying, as the BS security sublayers would
> sometimes need to forward messages between subnets or to different
> providers]
>
> Same L2-L3 argument as for key distribution above.
> Pre-auth and cunning key derivation schemes could indeed co-exist.
> I'm not sure if the world will thank us for picking 2 solutions
> though. It seems that effective pre-auth needs to be tied into the
> handover decision making entity (in the NMS?) since it is that
> that knows where it might want to pre-auth to. I suspect a similar
> line of reasoning applies to key derivation schemes. Either way,
> its an argument for putting the fast handover security messaging
> in the right place in the architecture.
>
>
> - Jeff Mandin
> Security Adhoc Chair
>
> DJ
>
>