Re: [Emu] EAP-GPSK: Ciphersuites

Hi Hannes,

a few comments inline:

> -----Original Message-----
> From: Hannes Tschofenig [mailto:Hannes.Tschofenig@gmx.net]
> Sent: Tuesday, August 22, 2006 2:20 AM
> To: M. Vanderveen
> Cc: emu@ietf.org
> Subject: Re: [Emu] EAP-GPSK: Ciphersuites
>
> Hi
>
> let us for a moment assume that RFC 4307 makes some
> reasonable algorithm choices (we are talking about IKEv2
> here). If we take the text and apply it to EAP-GPSK then we
> would produce something like:
>
> Conservative Choice:
> -----------------------
>
> (Integrity)
>        AUTH_HMAC_SHA1_96        2            [RFC2404]            MUST
>
> (Encryption)
>        ENCR_3DES                3         [RFC2451]       MUST-

I agree with Joe that AES is preferable to 3DES, barring some strong  
legacy considerations.

>
> (Key Derivation)
>        PRF_HMAC_SHA1       2          [RFC2104]    MUST

If it is a goal to conform to FIPS-140-2, that goal will probably  
drive the key derivation function choice in the direction of http:// 
www.ietf.org/internet-drafts/draft-dang-nistkdf-01.txt.    (I like  
HMAC as a KDF, but I am not confident that it is going to be approved  
for that purpose within FIPS-140-2.)

>
> (Note that there is no MUST for encryption algorithms specified in RFC
> 4307.)
>
>
> Choice for the Future:
> -----------------------
>
> (Encryption)
>       ENCR_AES_CBC             12        [AES-CBC]       SHOULD+
>
> (Integrity)
>       AUTH_AES_XCBC_96         5         [AES-MAC]       SHOULD+

OMAC is a better choice than XCBC, since it is FIPS-140 approved, and  
has some minor advantages (it's a refinement of XCBC that is  
unfortunately not backwards compatible with it).

>
> (Key Derivation)
>        PRF_AES128_CBC      4          [AESPRF]     SHOULD+
>

Same KDF considerations as above.

David

> Does this sound like a terrible bad idea?
>
> Ciao
> Hannes
>
> M. Vanderveen schrieb:
>> Both are pretty popular. Why not list them both? As for
> which one to be
>> mandatory to implement, someone should to a search through
> other systems
>> (e.g. IEEE, IPSec) and see which one is most popular.
>>
>> */Hannes Tschofenig <Hannes.Tschofenig@gmx.net>/* wrote:
>>
>>     Hi all,
>>
>>     the current version of the document
>>
> http://tools.ietf.org/wg/emu/draft-clancy-emu-eap-shared-secret-01.txt
>>     still supports AES-EAX:
>>
>>
> +-----------+----+-------------+---------------+--------------------+
>>     | CSuite/ | KS | Encryption | Integrity | Key Derivation |
>>     | Specifier | | | | Function |
>>
> +-----------+----+-------------+---------------+--------------------+
>>     | 0x000001 | 16 | AES-EAX-128 | AES-CMAC-128 | GKDF-128 |
>>
> +-----------+----+-------------+---------------+--------------------+
>>
>>     At the IETF#66 EMU meeting AES CCM was suggested.
>>
>>     Later, it got the impression that AES-CBC was more
> appreciated. Should
>>     we update the draft with AES-CBC?
>>
>>     Ciao
>>     Hannes
>>
>>
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>>
>>
>>
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