Original text:
Signed Statement is returned with the corresponding Registration Receipt embedded in the COSE unprotected header. <del> 2.1.3.2. </del>  One of the following:

Reviewer comments:
Strawman proposal for: URL PoC implementation here URL
Definite start in the right direction - I would say it is enough to get in and build on
general thumbs upLGTM After a chat with Richard Barnes, I think there are a few things happening with and key binding, that we should probably consider independently for scitt: Registration Policies that require fresh signatures from issuers. Registration Policies that require issuer's to commit to a recent tree head. Registration Policies that require additional context binding and a fresh signature from the issuer bound to special context. 1 and 2 are basically both about "time". If the Transparency Service does not trust the issuer to be honest about time, the transparency service can force the issuer to include a time commitment from the transparency service in their registration with binding to their confirmation public key. In the case the "nonce" is a timestamp, the TS rejects key binding tokens that are outside some window. In the case the "nonce" is a recent tree head, the TS rejects key binding tokens that are not to a tree head inside some window. In the case the "nonce" is a "challenge token", the nonce is some special context, the TS rejects key binding tokens that lack this special context. There is an opportunity to make the registration none interactive and one shot, assuming the following is acceptable: The key binding token nonce is a "recent timestamp / tree head" The transparency service rejects key binding tokens with nonces that are not "recent" There is an opportunity to make the registration interactive and context binding, assuming the following is acceptable: The transparency service includes specific context the issuer must commit to in their "challenge token". The issuer uses the challenge token as the nonce in their key binding token. The transparency service rejects key binding tokens with nonces that omit required context In this second case, imagine a "dynamic registration policy" Holder (Issuer) asks Verifier (Transparency Service) for a challenge token for a Customs Entry for 16056100. The transparency service knows that animal products require certificates to be imported, and issues a challenge token that looks like this: iss: "https://transparency.example" aud: "https://transparency.example" iat: ${now} exp: ${now + 7 day} currenttreehead: ... (not all TS are trees) currentpolicyhash: ... (not all policies are stored in trees) entrynumber: 42 htscodes: [ 16056100 ] The holder starts registering signed statements, each is bound to the same "challenge token". The first signed statement covers a phytosanitary certificate for the sea cucumber processing facility. The regulatory requirements change. The second signed statement covers the (now required) export certificate for sea cucumbers. The transparency service would normally have rejected the second signed statement, but because of the context in the challenge token, the transparency service knows that the second signed statement is now actually required. The holder did not need to request a "new challenge token" when the regulatory changes happened, and the holder still had to prove possession of the public key bound to both certificates ( and these public keys are different ). I chose to make this context scenario about sea cucumbers, but it could easily have been about network capable hardware devices that need to comply with regulations specific to Radio Antennas and GPUs... In those cases there would be firmware certifications required, and compliance requirements might change inside the transaction window. This also solves the problem of forcing the issuer to commit to the registration policies as they exist at the time the "challenge token" is issued. The TS can reject registrations that are committing to stale policies, or accept registrations that are commiting to stale policies, because the TS will know which policies the issuer is committing to by checking the challenge token. In the case that proof of possession is not required, and there is no need to commit to policies, the challenge token can be omitted, and the registration can proceed exactly as it is specified today. OS ORIE STEELE Chief Technology Officer www.transmute.industries

Revised text:
Signed Statement is returned with the corresponding Registration Receipt embedded in the COSE unprotected header.  <ins> 2.2.3.2. </ins> One of the following: