[Rats] Hint Discussion in CSR Attestation Draft

["Tschofenig, Hannes" <[e-mail]>]

Hi all,

I would like to come back to the hint discussion.

As Mike mentioned, we want to support use cases where the relying party and the verifier are separate roles. Note that two roles does not imply separate physical devices nor does it imply the verifier and the relying party to be operated by different operators. We also want to prevent the relying party from understanding the details of the evidence since this is what the verifier is supposed to do.

If there is only a single verifier that handles all evidence types from all vendors then it is trivial for the relying party to make a routing decision. Even if two or more vendors implement TPM-based attestation there is no problem with routing the evidence to the verifier. (Note that OIDs are typically assigned to evidence formats and not to vendors unless they are vendor-proprietary evidence formats.)

If there is more than one verifier then the story gets more interesting. If remote attestation will become more common, then we need to have a story of how to deploy such a system in a scalable way. The question is: how is going to work?

Unfortunately, the RATS working group has not provided an answer in their architecture document.

In the CSR attestation draft we suggested to use a hint, i.e. information that helps the relying party to select a verifier that can help process the evidence. Since this hint will not be used in all deployments, for example in deployments that only have a single verifier, this hint is optional. As such, those who do not want to use the optional hint do not need to look at it. For the other use cases it provides value.

Hence, I don’t really understand the objections and I don’t want to remove the hint!

Ciao
Hannes