eap Mailing List: Re: Re: Eap keying review: use of MSK/ EMSK for AMSK creation

[Yoshihiro Ohba (yohba]

On Tue, Nov 08, 2005 at 04:57:29PM -0500, Nakhjiri Madjid-MNAKHJI1 wrote:
> I think at least for handover or for MIP type applications we can work
> with this comfortably, i.e. have an HO-AMSK and a PMIP-AMSK and so on.
> And for HO, I will derive all the keys that are needed for HO-AMSK.
> 
> However, as we discussed during HOKEY meeting last night, this makes the
> assumption that the AAA nows at the time authentication, about all the
> applications for which it needs AMSKs for. 

I think this assumption has a limitation for MIPv6 bootstrapping.  In
some case, the AAA server may not know which HA is to be chosen by the
MN until an explicit request comes from HA x chosen by the MN.  In
this case, a key for HA x should be generated on-demand basis (but I
am not sure whether use of AMSK or MSK is appropriate for this case).

Yoshihiro Ohba


> This works for now, since we
> can say that a well designed system should make all AAA decisions
> (especially authorization ones) at once. Still it would be nice if do
> not add the limitation that prevents the AAA layer/ server to later ask
> for another keys, to be exact, if we do not require deletion of EMSK
> immediately after AMSK creation. I cannot come of a specific example
> right now.
> 
> Madjid
> 
> 
> >So this prohibits the AAA server to take EMSK and create new keys
> >  
> >
> We may have discussed this already, but this is I believe correct. The
> EMSK should not be handed to the lower layer. But see below:
> 
> >(AMSKs) for new applications or services.  This means the EAP layer 
> >must itself authorize each service application and calculate any AMSK 
> >that are needed for that application. Not only we are including a role 
> >of authorization into an EAP server, but also we are saying the EAP 
> >layer must anticipate all applications that need to derive their keys 
> >based on the EAP keying process. Should not be the AAA server to make
> >  
> >
> I think we can easily arrange things so that the AAA layer asks for
> AMSKs 1, 2, and 3, which fulfils security requirements (EMSK is not
> exposed) and does not require application knowledge from EAP layer. Does
> this work for you?
> 
> --Jari
> 
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