Issuer control of granularity and decomposability of claims

[stonematt]

In use case E.1 Digital Transcript (https://opencreds.github.io/vc-use-cases/#education), Joleen is spearheading the concept of a 'extended transcript' - My question is about the "basic transcript" - and how it's a model for any issuer tracking collections of evidence that may or may not be in a hierarchy.

In the simple university case, there is a hierarchy of achievements from coursework -> exams (grade) -> course completion -> degree. In general, issues decide how their claims can be represented in the marketplace. Focusing on the top 2 levels for a moment.

A university issuers, issues a VC for the "degree" with course completion as evidence, as a result:

1. Holder can share all data in the claim
2. Holder can share only the degree w/out evidence (is this a new claim w/out evidence?)
3. Holder cannot decompose the VC and share only 1 of the courses

-- Is Item 2 above the sort of thing we envision in 4.2 Assert Claim (https://opencreds.github.io/vc-use-cases/#assert-claim) where the holder can restrict the amount of information exposed?
-- Can the university require the full detail of the evidence anytime the claim is used?
-- If the exam was a distinct VC that included both score and grade as attributes, would we expect the issuer to be a able to mandate one as optional (like score) and one required (like grade)? This implies that issuer could mandate both attributes as required, thus restricting what the Holder can withhold.

[stonematt]

Supported if Issuer uses a ZKP or selective disclosure technology

[dlongley]

Also supported if the issuer constructs more than one credential (atomizes them as needed) to enable the holder to selectively disclose (where the selection choices are up to the options provided by the issuer via multiple VCs).

[jandrieu]

Update at least one use case to show the issuer explicitly making a credential with selective disclosure.

[jandrieu]

@dlongley or @stonematt Any interest in drafting a quick selective disclosure use case?

Our call for input is at https://lists.w3.org/Archives/Public/public-vc-wg/2023Apr/0000.html

Selective disclosure definitely would be a useful edition.

[jandrieu]

Turns out we have a selective disclosure use case in H.4 Traveling illness.

It might also make sense to add additional language for other existing use cases, e.g., E.1 Digital Transcript could be updated to explicitly state that the transcript could be used in different contexts with the individual revealing different bundles of school information, e.g., (1) graduated (2) graduated with GPA, (3) graduated with GPA with course list (4) graduated with GPA, course list and course grades.

We are open to PRs that might add such elements.

Given that we do have at least one selective disclosure use case, we're marking this pending closed, but other PRs in this direction would be welcomed.