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Re: [tcpm] I-D Action:draft-ietf-tcpm-tcp-auth-opt-01.txt

"Adam Langley" <agl@imperialviolet.org> Wed, 16 July 2008 17:39 UTC

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Date: Wed, 16 Jul 2008 10:40:06 -0700
From: Adam Langley <agl@imperialviolet.org>
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Subject: Re: [tcpm] I-D Action:draft-ietf-tcpm-tcp-auth-opt-01.txt
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On Tue, Jul 15, 2008 at 5:36 PM, Adam Langley <agl@imperialviolet.org> wrote:
> 2008/7/14  <Internet-Drafts@ietf.org>:
>>        Title           : The TCP Authentication Option
>>        Author(s)       : J. Touch, et al.
>>        Filename        : draft-ietf-tcpm-tcp-auth-opt-01.txt

Another thought: the keyid should be at the beginning of the MAC. We
want the options to be 4-byte aligned if at all possible and we want
the MAC to also be 4 byte aligned because CPUs have an easier time the
aligned data.

Currently (with the key ID at the end) the option, on the wire, looks like:
  NOP OPT 15 <12 bytes of MAC> KeyID   (16 bytes, 96-bit MAC)
or
  NOP OPT 19 <16 bytes of MAC> KeyID   (20 bytes, 128-bit MAC)

Both MACs are unaligned. Moving the KeyID to the beginning means that
the MACs would be 4-byte aligned:
  NOP OPT 15 KeyID <12 bytes of MAC> etc


Cheers,


AGL

-- 
Adam Langley agl@imperialviolet.org http://www.imperialviolet.org
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