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

[Nakhjiri Madjid-MNAKHJI1 (Madjid.Nakhjiri]

> 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?
> 
[Joe] I understand that there may be need for caching of certain
quantities.  I think Jari explained it well in a separate message.  In
my opinion you should try to identify the applications in use and the
keys needed as early as possible.  If this is not possible then caching
of the MSK may be necessary.  Do we have examples where the caching of
the EMSK is necessary.  In the case where key caching is used the cache
needs to be managed.  If we are caching EMSKs then the document that
describes EMSK usage must describe how key cache can be managed. 

Madjid>>I like to consider myself as an EAP keying consumer. I don't
really know what the cryptographic requirements for MSK or EMSK are? All
I know is that EMSK is recommended for creation of AMSK. Hence the need
for caching EMSK for future AMSK generation instances. I don't really
care about MSK at this point, because it is not used for AMSKs.

> Finally I have an slight issue with the statement that a KEY should be

> deleted so that it wont be used for other purposes.  I find that 
> statements like that are an over specification.  What makes anyone 
> think that making a statement that "X should/must be deleted" is going

> to be taken more seriously then "X should/must only be used for 
> purpose X and should/must not be transported out of Y"?
> 
> I think that whether it gets deleted or not is an implementation 
> issue.
> 

[Joe] The goal of the architecture is to prevent the re-use of keys for
multiple different purposes.  I agree that this is not necessarily the
same a deletion.  It is very important that keys derived from the EMSK
don't collide purposes across applications.  What happens in a
particular AMSK branch of the key hierarchy is not necessarily as
important since this branch is cryptographically separated from the rest
of the system through the AMSK derivation.  I think the current text
could probably do better in motivating why it is good practice to delete
keys.  

Madjid>>Are you saying EAP keying architecture is incapable of
supportring various keying needs? I like to have a tree with EMSK as a
root and one per application AMSK as each branch and hopefully
independent of other AMSKs, is that wrong?