Re: [IPsec] [ipsecme] #112: Truncation of SHA-1 ICVs

[Scott C Moonen <[e-mail]>]

Hi Sheila,

1) I don't think we can expand the registry to include non-truncated 
versions of HMAC-SHA2-*.  RFC 4868 stipulates for IKE and IPsec in general 
that the authenticator length "is always half the output length of the 
underlying hash algorithm."

2) RFCs 3566, 4494 are worded a bit more permissively for AES-XCBC and 
AES-CMAC, so perhaps there's some wiggle room there.

3) I'm not sure if HMAC-RIPEMD is defined for use in IKE (there is not 
even an algorithm identifier for IKEv2), but its use for AH and ESP (RFC 
2857) currently only defines a truncated form of the algorithm.


Scott Moonen ([e-mail])
z/OS Communications Server TCP/IP Development
http://www.linkedin.com/in/smoonen



From:
"Frankel, Sheila E." <[e-mail]>
To:
"[e-mail]" <[e-mail]>
Cc:
Tero Kivinen <[e-mail]>, Paul Hoffman <[e-mail]>, 
"[e-mail]" <[e-mail]>
Date:
10/27/2009 11:46 AM
Subject:
Re: [IPsec] [ipsecme] #112: Truncation of SHA-1 ICVs




#112: Truncation of SHA-1 ICVs

Proposed change to Roadmap doc:

Add text to Section 5.3 (Integrity-Protection Algorithms)

Current text:
   The integrity-protection algorithm RFCs describe how to use these
   algorithms to authenticate IKE and/or IPsec traffic, providing
   integrity protection to the traffic.  This protection is provided by
   computing an Integrity Check Value (ICV), which is sent in the
   packet.  The RFCs describe any special constraints, requirements, or
   changes to packet format appropriate for the specific algorithm.  In
   general, they do not describe the detailed algorithmic computations;
   the reference section of each RFC includes pointers to documents that
   define the inner workings of the algorithm.  Some of the RFCs include
   sample test data, to enable implementors to compare their results
   with standardized output.

Additional text:
   Some of these algorithms generate a fixed-length ICV, which is 
truncated 
   when it is included in an IPsec-protected packet. For example, standard 

   HMAC-SHA-1 generates a 160-bit ICV, which is truncated to 96 bits when 
it 
   is used to provide integrity-protection to an ESP or AH packet. The 
   individual RFC descriptions mention those algorithms that are 
truncated. 
   When these algorithms are used to protect IKEv1 SAs, they are not 
   truncated. For HMAC-SHA-1 and HMAC-MD5, the IKEv2 IANA registry 
contains 
   values for both the truncated version and the standard non-truncated 
   version; thus, IKEv2 has the capability to negotiate either version to 
   protect IKEv2 and/or IPsec-v3 SAs.  For the other algorithms (AES-XCBC, 

   HMAC-SHA-256/384/512, AES-CMAC and HMAC-RIPEMD), only the truncated 
   version can be used for both IKEv2 and IPsec-v3 SAs.
 
NOTE to Tero, Paul, Yaron: do we want to expand the IKEv2 IANA registry to 
include non-truncated AES-XCBC-MAC, HMAC-SHA-256/384/512, AES-CMAC and 
HMAC-RIPEMD?


________________________________________
From: ipsecme issue tracker [[e-mail]]
Sent: Friday, October 16, 2009 8:25 PM
To: [e-mail]; Frankel, Sheila E.
Subject: [ipsecme] #112: Truncation of SHA-1 ICVs

#112: Truncation of SHA-1 ICVs
-----------------------------------+----------------------------------------
 Reporter:  paul.hoffman@…         |       Owner:  sheila.frankel@…
     Type:  defect                 |      Status:  new
 Priority:  normal                 |   Milestone:
Component:  roadmap                |    Severity:  -
 Keywords:                         |
-----------------------------------+----------------------------------------
 In RFC 2404, it mentions that SHA-1 ICVs are truncated to 96 bits for
 IPsec.  We should also mention in Section 5.3 that this truncation is 
done
 for IKEv2 as well. Same for RFC 2403. Text is needed.

--
Ticket URL: <http://trac.tools.ietf.org/wg/ipsecme/trac/ticket/112>
ipsecme <http://tools.ietf.org/ipsecme/>

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