Subject: [Emu] idraft-arkko-eap-aka-kdf-09 and AT_CHECKCODE

From: Jouni Malinen <[email-masked]>
Date: Wed, 12 Nov 2008 19:44:19 +0200

It looks like draft-arkko-eap-aka-kdf-09.txt updates the RFC 4187
definition of AT_CHECKCODE by changing the length of Checkcode field to
be "0 or 32 bytes". This does not look correct since EAP-AKA continues
to use 20-byte Checkcode value and the same definition of the attribute
is shared by both EAP-AKA and EAP-AKA' (assuming I understood the draft
correctly). The updated version should include 20 bytes as a valid
length of the Checkcode field (i.e., something like "0, 20, or 32
bytes"). In addition, the following paragraph ("Second, the checkcode is
a hash value ..") should be modified to apply only for EAP-AKA' and only
when using AT_KDF Key Derivation Function value 1.

-- 
Jouni Malinen                                            PGP id EFC895FA
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From: Jari Arkko <[email-masked]>
Date: Thu, 13 Nov 2008 15:27:46 +0200

Jouni,

> when using AT_KDF Key Derivation Function value 1.

Thanks for your review.

I have thought about this issue today and came to the following 
conclusion. The issue is about being clear where the new formats and 
rules apply. They only apply to EAP-AKA', not EAP-AKA or EAP-SIM. It 
would be possible to change the attribute type numbers and names as 
well, but personally I find that unnecessary. So here's what I'd suggest:

In Section 3.4.2, change

OLD:
The AT_MAC attribute is changed as follows.
NEW:
When used within EAP-AKA', the AT_MAC attribute is changed as follows.

In Section 3.4.3, change
OLD:
The AT_CHECKCODE attribute is changed as follows.
NEW:
When used within EAP-AKA', the AT_CHECKCODE attribute is changed as 
follows.

(We may get an OK from the 3GPP to approve this spec this week. However, 
I have this change and another one (picture reformatting to fit it in 
one page. The latter is hard to do in an RFC Editor note, so I guess 
I'll submit a new version of the draft next week in any case.)

Jari