Subject: [Ipsec] Integrity key size

From: Alejandro Pérez Méndez<[email-masked]>
Date: Thu, 28 Jul 2005 17:51:00 +0200

Hi,

I'm implementating IKEv2 protocol and I'm confused about the key size to
be used in integrity protection when using AUTH_MD5_96 and AUTH_SHA1_96
algorithms.
The section 2.13 in the IKEv2 draft says: 

        << ... For integrity protection functions based on HMAC, the
        fixed key size is the size of the output of the underlying hash
        function. ... >>

So, whats the SK_ai (and SK_ar) key correct size that must be used, 128
bits for MD5 and 192 for SHA-1 or 96 bits for both? Note I'm referring
to the key size, not the digest size that is clearly 96 bits.

Another thing: Linux IPsec stack has SHA1 and MD5 integrity algorithms,
but they use all bytes, not only the first 96 bits as SHA1_96 and MD5_96
do. What is the Transform id that must be included in the PAYLOAD_SA on
the CREATE_CHILD_SA exchange to negociate them?

Thanks.

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---

From: Michael Bowler <[email-masked]>
Date: Thu, 28 Jul 2005 12:04:41 -0400

> to the key size, not the digest size that is clearly 96 bits.

Based on the output size of underlying hash function, the key sizes 
would be:
   MD5   = 128 bits
   SHA-1 = 160 bits

Cheers,

Michael

-- 
Michael Bowler                                [email-masked]
IC Design Engineer                                  (613) 254-5456x107
Elliptic Semiconductor                            www.ellipticsemi.com