It should be possible to submit evidence for verification without having to open a session first, i.e. without challenge-response. The verifier-provided challenge/nonce is not needed for freshness in all scenarios. In such cases, having to open a session first creates unnecessary network traffic and round trips. For example, the challenge included in attestation evidence may be channel bindings for a secure channel where the attester and the relying party are the endpoints. In this case, verifying freshness is the task of the relying party instead of the verifier.
It should be possible to submit evidence for verification without having to open a session first, i.e. without challenge-response. The verifier-provided challenge/nonce is not needed for freshness in all scenarios. In such cases, having to open a session first creates unnecessary network traffic and round trips. For example, the challenge included in attestation evidence may be channel bindings for a secure channel where the attester and the relying party are the endpoints. In this case, verifying freshness is the task of the relying party instead of the verifier.