[Rats] Requesting a Nonce from a Verifier

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Hi all,

 

Hendrik and I have been working on an update of the CMP/EST extensions, which allow an Attester to request a nonce via the Relying Party (in the background check model). This “nonce draft”, see draft-tschofenig-lamps-nonce-cmp-est, aims to provide freshness for the CSR attestation draft (see draft-ietf-lamps-csr-attestation).

 

We have been wondering about the design of this protocol interface. At a minimum, the attester needs to indicate the length of the nonce being requested from the verifier. EAT, however, supports also an array of nonces in the nonce claim. Should such a protocol interface allow a request for multiple nonces? 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. Should the request for a nonce also include information about the attestation technology supported by the attester?

 

We thought that this type of foundational feature is described in detail in one of the RATS working group documents and the draft-ietf-rats-reference-interaction-models seemed like a good starting point for such details. Unfortunately, this document falls short in explaining these types of aspects because it is heavily focused on a specific TPM deployment.

 

Has someone in the group thought about this aspect already or has otherwise gained experience with this aspect?

 

Ciao

Hannes