Subject: [MSEC] MIKEY DH related doubts

From: "Ibrahim, Maideen" <[email-masked]>
Date: Tue, 13 Apr 2004 12:06:54 -0400

Hi,

I am trying to find out the answers for the following questions. I am
implementing MIKEY for key management for SIP.

1. MIKEY supports DH key exchange by having a separate payload and a value
in the common header. When Iooked into section 6.4
(ietf-draft-msec-mikey-08.txt) for DH payload, I don't see much explanations
for DH group and DH value. What is DH group? Does DH value denote the g^s *
p (g - generator, s - secret number, p - big prime number)?

2. DH needs p (prime) and g (generator) to be public. How these numbers are
exchanged using MIKEY? or Is it to be static, known to communicators by
other means??

Thanks,

Maideen

---

From: "Fredrik Lindholm (KI/EAB)" <[email-masked]>
Date: Thu, 15 Apr 2004 08:14:26 +0200

Hi Maideen,

see comments below.

> -----Original Message-----
> From: Ibrahim, Maideen [mailto:[email-masked]]
> Sent: den 13 april 2004 18:07
> To: [email-masked]'; Elisabetta Carrara (KI/EAB)
> Subject: MIKEY DH related doubts
> 
> 
> Hi,
> 
> I am trying to find out the answers for the following questions. 
> I am implementing MIKEY for key management for SIP.
> 
> 1. MIKEY supports DH key exchange by having a separate payload and 
> a value in the common header. When Iooked into section 6.4 (ietf-
> draft-msec-mikey-08.txt) for DH payload, I don't see much explanations 
> for DH group and DH value. What is DH group? Does DH value denote the 
> g^s * p (g - generator, s - secret number, p - big prime number)?

You generally denote the DH-value as "g^s mod p". The DH-value is defined 
in Section 3.3 but see also e.g. [HAC] for more info on the basics of DH 
exchanges. 

> 2. DH needs p (prime) and g (generator) to be public. How these 
> numbers are exchanged using MIKEY? or Is it to be static, known to 
> communicators by other means??

MIKEY uses currently the well known OAKLEY groups (see [OAKLEY]), which 
are signalled (see Section 6.4) by:

   * DH-Group (8 bits): identifies the DH group used.

     DH-Group      | Value | Comment       | DH Value length (bits)
     --------------------------------------|---------------------
     OAKLEY 5      |     0 | Mandatory     |  1536
     OAKLEY 1      |     1 |               |   768
     OAKLEY 2      |     2 |               |  1024

Please, see also Section 4.2.7 and 4.2.9 (for info on how to add new 
groups).

[OAKLEY] Orman, H., "The Oakley Key Determination Protocol", RFC
2412, November 1998.

[HAC] Menezes, A., van Oorschot, P., and Vanstone, S., "Handbook of
Applied Cryptography", CRC press, 1996.

/Fredrik
 
> Maideen

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