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

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Eric Rescorla wrote:
> At Mon, 02 Feb 2009 21:07:28 -0800,
> Joe Touch wrote:
>>
>>
>> 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
> 
> Well, Joe, since you brought it up, this whole architecture
> you've invented for the internal structure (TSAD, etc.) is the
> source of the clumsiness, not the need for variable parsing.

OK, let's call the place where the connection info is stored the STORE.
Then the steps still become:

- - get the keyID from the packet
- - go to the STORE to find out how long the MAC is
- - pass the keyID and (optionstart + len - maclen)

Still three steps, vs one:

- - pass the keyID and (optionstart + 2)

Note that the second way doesn't need to go to a separate table of
information to figure out how to finish parsing the packet. Regardless
of what you call it or where you put it, this takes multiple steps and
consulting the STORE before you can pass the required information to the
verification algorithm.

Joe
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