Re: [Rats] Requesting a Nonce from a Verifier

["Smith, Ned" <[e-mail]>]

@hannes.tschofenig=[e-mail]<mailto:hannes.tschofenig=[e-mail]> – did you get your questions answered?

  1.  At a minimum, the attester needs to indicate the length of the nonce being requested from the verifier.
  2.  EAT, however, supports also an array of nonces in the nonce claim. Should such a protocol interface allow a request for multiple nonces?
  3.  Furthermore, the Attester may also need to provide information about the Verifier. This is necessary when there are many Verifiers in the system and not everyone of them might be able to successfully verify the Evidence.
  4.  Should the request for a nonce also include information about the attestation technology supported by the attester?

Note that I-D. csr-attestation describes a PKIX deployment where the RA is the RATS relying party and interacts with at least one RATS verifier.

The RATS roles, possibly confusingly, aren’t entities, nevertheless nonces (freshness / recentness) apply to entities in some deployment context. RATS Arch may be insufficient to resolve the freshness recentness architectures.

I think it’s reasonable that the entity requesting Evidence could be integrated with multiple Verifier entities, each expecting some sort of freshness indication. If multiple verifiers supply multiple nonces, then the context for which nonce belongs to which Verifier needs to be preserved.

Question (4) could be a bit tricky since trust in the attester may be understood in terms of Attester composition where one component may depend on another component such as in DICE layering or TPM trust chains. Presumably, Evidence has enough context for Verifiers to decipher Attester composition such that the trust dependencies can be walked to some logically meaningful description of the Attester as a protocol end point. It may be necessary for nonces to have Attesting Environment context too such that freshness of each AE in an Attester composition is knowable.

-Ned

From: Carl Wallace <[e-mail]>
Date: Thursday, March 7, 2024 at 07:51
To: Thomas Fossati <[e-mail]>, Smith, Ned <[e-mail]>
Cc: Henk Birkholz <[e-mail]>, hannes.tschofenig=[e-mail] <hannes.tschofenig=[e-mail]>, [e-mail] <[e-mail]>
Subject: Re: [Rats] Requesting a Nonce from a Verifier
Inline...

On 3/6/24, 11:36 PM, "RATS on behalf of Thomas Fossati" <[e-mail] <mailto:[e-mail]> on behalf of [e-mail] <mailto:[e-mail]>> wrote:


On Wed, Mar 6, 2024 at 5:54 PM Smith, Ned <[e-mail] <mailto:[e-mail]>> wrote:
> I'm not sure I understand Hanne's use case. Is the CA doubling as the RATS Verifier?


No, the CA is the RP. The CA trusts one or more verifiers.


>If not, why does one CA need attestation results from multiple Verifiers


I guess it is to support devices that produce composite evidence.

[CW] Or just different types of devices, i.e., iOS devices, TPMs, Android devices, etc.

<snip>