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

[Nakhjiri Madjid-MNAKHJI1 (Madjid.Nakhjiri]

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)


In both cases we require deletion of EMSK after generation of AMSK, why?

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. 

> _________________________________________________________________
> To unsubscribe or modify your subscription options, please visit:
> http://lists.frascone.com/mailman/listinfo/eap
> 
> Arhives: http://lists.frascone.com/pipermail/eap
>