Subject: Re: [Emu] I-D Action:draft-ietf-emu-eap-gpsk-07.txt

From: Charles Clancy <[email-masked]>
Date: Tue, 04 Dec 2007 16:46:04 -0500

Jouni,

Thanks for your comments.  They have been addressed in v08.

http://www.ietf.org/internet-drafts/draft-ietf-emu-eap-gpsk-08.txt

--
t. charles clancy, ph.d.                 eng.umd.edu/~tcc
electrical & computer engineering, university of maryland

Jouni Malinen wrote:
> On Mon, Nov 19, 2007 at 03:50:02AM -0500, [email-masked] wrote:
> 
>> 	Title           : EAP Generalized Pre-Shared Key (EAP-GPSK)
>> 	Filename        : draft-ietf-emu-eap-gpsk-07.txt
> 
> Minor editorial comments:
> 
> It looks like the general description of MK derivation in '4. Key
> Derivation' was not updated to match with the ciphersuite specific
> changes in 7.1.3 and 7.2.3.
> 
> The following lines:
>    o  inputString = RAND_Peer || ID_Peer || RAND_Server || ID_Server
>    o  zero = 0x00 || 0x00 || ... || 0x00 (KS times)
> 
>    o  MK = KDF-KS(zero, PL || PSK || CSuite_Sel || inputString)[0..KS-1]
> 
> would need to be changed to:
>    o  inputString = RAND_Peer || ID_Peer || RAND_Server || ID_Server
> 
>    o  MK = KDF-KS(PSK[0..KS-1], PL || PSK || CSuite_Sel || inputString)[0..KS-1]
> 
> 
> 
> 
> 7.1.3 and 7.2.3:
> 
>    MK = GKDF-16 (PSK[0..127], PL || PSK || CSuite_Sel || inputString)
>    MK = GKDF-32 (PSK[0..255], PL || PSK || CSuite_Sel || inputString)
> 
> The 0..127 and 0..255 are clearly usings bits, but these should be bytes
> to be consistent with the 0..KS-1 style used elsewhere, i.e., these
> lines should be
> 
>    MK = GKDF-16 (PSK[0..15], PL || PSK || CSuite_Sel || inputString)
>    MK = GKDF-32 (PSK[0..31], PL || PSK || CSuite_Sel || inputString)
> 
> 
> Now that definition of 'zero' was removed from MK derivation, Method-ID
> derivation is using implicitly defined 'zero'. Even though it is
> relatively obvious what length will be used here, it would be better to
> state this explicitly:
> 
> Add following line to 7.1.3 before Method-ID derivation:
> zero = 0x00 || 0x00 || ... || 0x00 (16 times)
> 
> Add following line to 7.2.3 before Method-ID derivation:
> zero = 0x00 || 0x00 || ... || 0x00 (32 times)
> 
> 
> Especially the ciphersuite 2 case would benefit from explicit statement
> since HMAC-SHA256 could use any key length. I don't see any particular
> need for this to be 32 octets, but that would be consistent with other
> uses of GKDF and anyway, this matches with the KS-octet 'zero' used in
> Ch. 4.
> 

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