Re: [Emu] Review of draft-ietf-emu-eap-gpsk-08 (1st round of comments)

["Dan Harkins" <dharkins at lounge.org>]

  Hi Charles,

On Fri, June 27, 2008 8:05 am, Charles Clancy wrote:
[snip]
>> S6 and elsewhere: Several places in the document assume that KS (key
>> size of the ciphersuite) is always the same as the MAC output length.
>> This would make it difficult to define ciphersuites based on
>> e.g. AES-CMAC-256. If this restriction is intentional (and WG is happy
>> with it), at the very least it needs to be emphasized much more.
>
> I'm not sure what AES-CMAC-256 means.  RFC 4493 defines CMAC
> specifically for 128 length AES, so if you wanted to something involving
> 256, you'd need to define exactly what AES-CMAC-256 was, and I imagine
> it would have a 256-bit input and a 256-bit output.  Regardless, I added
> a statement in the key derivation section saying the input and output
> lengths of your ciphersuite must be equal.

  CMAC is defined in NIST SP 800-38B and section D.3 deals with the
instance of CMAC-AES-256 (with test vectors!). It takes a 256-bit key
and, like all AES-based MACs, produces a 128-bit digest.

  regards,

  Dan.



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