Linkability and issuer involvement as a protocol requirement #279
Description
This issue is filed as a follow-up to feedback in #260 from @martinthomson and @simoneonofri, highlighting that we have not clearly defined which linkability properties the specification wants to require from protocols.
From my perspective, I believe that we want the API to be generally agnostic to selective disclosure and linkability and support the exchange of inherently linkable and/or identifiable attributes, attributes with verifier-verifier unlinkability, and e.g. ZKPs for verifier-issuer unlinkability.
Protocol requirements should allow for all of these things to happen.
I would apply the same principle to issuer involvement: Verifier - issuer unlinkability might not be practical or needed for the majority of use cases, but that doesn't mean we shouldn't encourage adoption of technologies that reduce issuer exposure to information and "phone home" in general, as there should be a difference between the hypothetical capability for a verifier to communicate a user's credential back to the issuer and whether it happens in practice.