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

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Eric Rescorla wrote:
> At Tue, 03 Feb 2009 08:34:53 -0800,
>> 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.
> 
> Again, I wouldn't construct the system this way.
> 
> Rather, you hang the information required to process each connection
> off the connection itself. This is how pretty much every SSL/TLS stack
> works.

I don't think you're seeing the extra work; you're focusing too much on
the assumption that the STORE is in a single place. OK, so let's call
the place where the properties of a connection are in TCB++ (note that
the TSAD isn't the place you go for every packet; you can easily keep
connection info in the TCB++, and an implementation probably will, and
we already note that in the ID).

So the steps are still:

- - get the keyID from the packet
- - check the TCB++ to figure out where the MAC is
- - pass the keyID and (optionstart + len - maclen) to the algorithm

The point is that you can't parse the option without extra info that is
stored elsewhere - i.e., not in the packet. Whether it's central or in
the TCB++ is not the point.

Joe
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