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Re: [tcpm] TCP-AO: Text for New_Key Process

Joe Touch <touch@ISI.EDU> Tue, 03 February 2009 05:08 UTC

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From: Joe Touch <touch@ISI.EDU>
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To: Eric Rescorla <ekr@networkresonance.com>
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Cc: tcpm@ietf.org, Allison Mankin <mankin@psg.com>, skonduru@juniper.net
Subject: Re: [tcpm] TCP-AO: Text for New_Key Process
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Eric Rescorla wrote:
...
>>> Well, I don't really favor they ke flag approach, but it occurs to
>>> me that this is easily fixed by replacing the key flag with a 
>>> "ready to use" byte. Recall that the length of the MAC is tied
>>> to the key so if you know the key-id you know the length of the
>>> MAC. This makes the Length byte partly redundant. Accordingly,
>>> you could have the following format:
>>>
>>>  - Kind (1)
>>>  - Length (1)
>>>  - Key-ID (1)
>>>  - Ready-keys [variable]
>>>  - MAC
>> That is variable length, even when the active key has not changed; that means
>> conditional parsing is required, which is cumbersome.
> 
> s/cumbersome/trivial/

Well, if trivial means the following, sure:

1) get the keyID
2) go to the TSAD to get the MAC length
3) pass the KeyID and the MAC pointer = (option start + length - 
mac_length) to the verification alg

Compare that with the current option:

1) pass the keyID and the MAC (i.e., option start + 2) to the 
verification algorithm

Joe

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