Re: [STDS-802-16-MOBILE] [security] Summary of issues and requirements for PKMv2
Dear Loeke,
I think that starting with defining what is broadcast is a good direction,
and I fully accept your analysis. Regarding the 'multimedia broadcast', this
is a term that is defined at the network level, not at the cell level, and
is the same kind of broadcast that is used by your TV set and radio
(although both are analog) to receive data from a broadcaster.
You can of course claim that we can do such network level broadcast as
broadcast within each and every cell (or sector), but such type of broadcast
has very low efficiency (it has to use the most robust and hence least
efficient modulation, and combat against interference from neighbor cells).
The idea behind multimedia broadcast is to transmit the broadcast
information to all cells across the network in a synchronized manner such
that instead of destructive interference, signals from neighbor cell will
add and create a macro-diversity effect. Such an effect would enable use of
much more efficient modulation and coding for the broadcast multimedia
content.
Regards,
Yigal
-----Original Message-----
From: Brederveld, Loeke (loeke) [mailto:brederveld@agere.com]
Sent: Thursday, May 27, 2004 4:02 PM
To: Yigal Leiba; STDS-802-16-MOBILE@listserv.ieee.org
Subject: RE: [STDS-802-16-MOBILE] [security] Summary of issues and
requirements for PKMv2
Hi Yigal, all,
I agree fully with you last sentence, that we have to make sure
everybody means the same thing using the term "broadcast", and for me,
coming from the data world, I seen already problems there. May be this
is an open door, but let's try to define the variuos 'broadcasts'
MAC level Broadcast: those MAC level frames which are intended for all
stations in a subnet. In Ethernet / 802.11 network addressed with the
destination MAC address ff ff ff ff ff ff.
IP level Broadcast: those IP level frames which are intended for all IP
stations, usualy only in a single IP subnet (else you can have big
problems :-) ). IP broadcast (255.255.255.255) do use the MAC level
Broadcaat destination address also.
Furthermore, you have MAC and IP level Multicasts: frames which are
intended to a select group of stations within an subnet. The station
itself can decide it will receive certain multicasts. IP level
Mulicats/Broadcast normally uses also MAC level Multicast/Broadcats
addressing.
I assume the "Multimedia broadcast" is an application level broadcast
(video and/or audio broadcast). Usualy these applications are using IP
level multicast (not all stations are interested in the application
level broadcast). In a single cell of a wireless data system, certainly
for 802.11 but as I understand, it is the same for 802.16, a multicast
is only transmitted once, and is encrypted with a groupkey which is
available to all authenticated stations in the cell.
With this in mind, I don't understand your concern: all stations in the
cell do receive the applcation broadcast content at the same moment.
Only the latency of their internal processing will cause a slight
difference in the moment the content is made available to the enduser.
Different cells will transmit the multicast on different times depending
e.g. on the length of the output queues, but depending on the QOS
parameters set for the type of traffic, the difference will be within
the acceptable latency period for that type of traffic, e.g. 50 ms. I
can't imagine this will be problem?
Loeke
-----Original Message-----
From: owner-stds-802-16-mobile@listserv.ieee.org
[mailto:owner-stds-802-16-mobile@listserv.ieee.org] On Behalf Of Yigal
Leiba
Sent: Tuesday, May 25, 2004 22:16
To: STDS-802-16-MOBILE@listserv.ieee.org
Subject: 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
>
>