[Rats] Should we remove submods from EAT? (was Re: EAT Review Comments)

[Laurence Lundblade <[e-mail]>]

Lots discussion on EAT. :-)

Chunking through it...

> On Dec 9, 2021, at 2:45 AM, Hannes Tschofenig <[e-mail]> wrote:
>> Laurence wrote:
>> There’s strong logic here:
>> — RATS architecture explicitly calls out composite attestation — A submodule can be a nested EAT to implement composite attestation — A nested EAT can be a CWT, UCCS  or DEB — The CDDL that specifies a nested EAT submodule thus must mention UCCS
>> 
>> So a UCCS is a claim that goes into a CWT. I think UCCS, particularly CDDL for UCCS, must be included because of this.
> 
> [Hannes] I wonder whether everything in the RATS architecture should be covered in the EAT specification for several reasons:
> - First, the EAT spec becomes complex and harder to read.
> - Second, the RATS architecture enumerates everything that came into someone's mind or, as we later learned, can be patented.
> - Given the status of the industry with attestation I believe it will take a while to even get the basic functionality deployed. For more complex use cases it can easily take several years.

In the above, I said that RATS architecture has composite attestation and therefor we need EAT submods. Hannes is maybe suggesting we don’t need submods because they add too much complexity.

Here’s a few more reasons for submods:

- Complex devices like phones, routers and cars have a large number of subsystems. For the router case, you may have individual attestation from cards in the router and one for the chassis. A mobile phone has like 10 major compute environments (TEE, camera, modem, low power audio, CPU/GPU…) We need a way to express and organize claims for all sorts of complex devices.

- submods give EAT a very substantial expressive power for all sorts of use cases. Not having them would result in people inventing ad hoc schemes for their use cases.


- I recall a few conversations with various folks that see important for submods in their use cases


I have a strong conviction that submods, including nested tokens, are necessary for EAT now and are worth the complexity they add. 

LL

(Happy to consider improvements to the submods design)
(Submods != UCCS/UJCS; UCCS and UJCS are related, but can be a separate decision)