eap Mailing List: RE: Strawman -10/EMSK deletion requirement?

[Nakhjiri Madjid-MNAKHJI1 (Madjid.Nakhjiri]

Hi Avi, 

-----Original Message-----
From: Avi Lior [mailto:avi [at] bridgewatersystems.com] 
Sent: Thursday, March 02, 2006 2:16 PM
To: Salowey, Joe; Nakhjiri Madjid-MNAKHJI1; Rafa Marin Lopez; Bernard
Aboba
Cc: eap [at] frascone.com
Subject: RE: [eap] Strawman -10/EMSK deletion requirement?

Hi Joe and Madjid,

The only reason for caching the EMSK is if you have to generate an AMSK
for another application associated with the current session.

Madjid>> Thank you for clarification. Another example may be roaming to
another access technology!!

So the question is do you have to generate all possible AMSKs and then
delete the EMSK or can you generate the AMSKs as needed?

Madjid>>i.e. keep EMSK for future AMSK generation. The first option will
create the need for running EAP again.

> -----Original Message-----
> From: Salowey, Joe [mailto:jsalowey [at] cisco.com]
> Sent: Thursday, March 02, 2006 2:49 PM
> To: Nakhjiri Madjid-MNAKHJI1; Rafa Marin Lopez; Bernard Aboba
> Cc: eap [at] frascone.com
> Subject: RE: [eap] Strawman -10/EMSK deletion requirement?
> 
>  
> 
> > -----Original Message-----
> > From: Nakhjiri Madjid-MNAKHJI1 [mailto:Madjid.Nakhjiri [at] motorola.com]
> > Sent: Thursday, March 02, 2006 8:44 AM
> > To: Salowey, Joe; Rafa Marin Lopez; Bernard Aboba
> > Cc: eap [at] frascone.com
> > Subject: RE: [eap] Strawman -10/EMSK deletion requirement?
> > 
> > Hi Joe,
> > 
> > Thanks for the email. I think you responded to the old piece of the 
> > email from Rafa and I am to blame for causing that confusion, as I 
> > kept that part to provide context.
> > Again, my question was why an entity needs to delete EMSK after 
> > generating the first AMSK (or first set of AMSKs?)? This
> seems to be
> > the requirement regardless of two options:
> > 
> > 1) keep EMSK at EAP layer, create AMSK at EAP layer based
> request from
> > AAA layer, delete EMSK Immediately (this means EAP layer must have 
> > KDFs for AMSK=KDF(EMSK, etc)
> > 2) push EMSK down to AAA layer at backend server, create
> AMSK at AAA
> > layer and delete EMSK immediately (this means AAA layer must have
> > KDFs)
> >
> [Joe] If the AAA layer contains the AAA client and AAA server then the

> EMSK should not be available to this layer, if the AAA layer means 
> something else then I don't know about (1).
> The AMSK should be generated in the EAP and exported, option (2).
>  
> > 
> > In both cases we require deletion of EMSK after generation of AMSK, 
> > why?
> > 
> [Joe] To minimize the chance of exposure of the EMSK.  Why do you need

> to cache it? Could you generate and cache an AMSK instead?
> 
> 
> > Thanks,
> > 
> > Madjid
> > 
> > -----Original Message-----
> > From: Salowey, Joe [mailto:jsalowey [at] cisco.com]
> > Sent: Wednesday, March 01, 2006 5:17 PM
> > To: Nakhjiri Madjid-MNAKHJI1; Rafa Marin Lopez; Bernard Aboba
> > Cc: eap [at] frascone.com
> > Subject: RE: [eap] Strawman -10
> > 
> >  
> > 
> > > -----Original Message-----
> > > From: Nakhjiri Madjid-MNAKHJI1
> [mailto:Madjid.Nakhjiri [at] motorola.com]
> > > Sent: Wednesday, March 01, 2006 2:38 PM
> > > To: Rafa Marin Lopez; Bernard Aboba
> > > Cc: eap [at] frascone.com
> > > Subject: RE: [eap] Strawman -10
> > > 
> > > Madjid>>Again, why is deletion of EMSK after generation of
> > > one AMSK is a
> > > requirements. What if we need to create multiple AMSKs
> and that at
> > > multiple occassions?
> > > 
> > > 
> > > 
> > > Well, actually, lower layer authenticator implementation
> > should expect
> > > (MSK,EMSK) in the case EAP method is executed by the standalone 
> > > authenticator or (MSK,AMSK) in the case EAP method is executed by 
> > > backend authentication server. If it receives (MSK,EMSK)
> > should create
> > 
> > > AMSK and delete EMSK. If it receives (MSK,AMSK) , that's
> > all, correct?
> > 
> > [Joe] Not really, strictly speaking the lower layer
> shouldn't expect
> > to receive the EMSK as that would break mode independence.  An 
> > architectural description should not have the lower layer receiving 
> > the keys. From a supplicant perspective it must appear the same 
> > whether an external EAP-Server or a collocated EAP server is used.
> > Now I don't know what is going on inside your box, it could all be 
> > monolithic when a internal EAP server is used but that shouldn't be 
> > visible to the external world.  If I was interested in
> cryptographic
> > module separation I might not be too happy if you shared
> the EMSK with
> > the lower layer.
> > 
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