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