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2023-05-08 AnonCreds Specification Working Group Meeting

2023-05-08 AnonCreds Specification Working Group Meeting

May 08, 2023

Summary

  • Update on the AnonCreds V2.0 Working Group

  • Unrevealed attributes

  • Checkin: anoncreds-rs implementation progress, requests

  • Open Discussion

Recording of Call: dummyfile.txt



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Meeting Attendees

@Stephen Curran (BC Gov / Cloud Compass Computing Inc.) <swcurran@cloudcompass.ca>

@Steve McCown (Anonyome Labs) <smccown@anonyome.com> 



Related Repositories:

Meeting Preliminaries:

  • Welcome and Introductions

  • Announcements

    • Presentation at VC-API Working Group

  • Any updates to the Agenda?

Agenda

Open Issue

  • Update on the AnonCreds V2.0 Working Group

    • Previous Meeting: Revisiting the Issuance data models – do we need an extra "attributes repository" object?

      • Same objects as AnonCreds 1 – Schema, Credential Definition, Credential

      • Schema adds types information on attributes – cryptographic types (string, numeric, scalar, enumeration, range)

      • Proposed addition of new "Schema Claims" object that is effectively a "repository of claims" to be shared across schemas

        • Name, type, validators defined at either the Schema Claims level or at the Schema level

    • Next week: Presentation Data Models

  • PRs for review and merging

  • Issues to Discuss – None.

  • Unrevealed Attributes, cryptographic vs. business-level verification, and related issues:

    • Core issue – cryptographic verification vs. business purpose verification. 

      • Where does the AnonCreds specification end, and the Present Proof protocol take over?

    • Clarification of the behaviour of unrevealed attributes. Based on recent message on Discord – gmulhearn

      • Unrevealed attributes are the same as selective disclosure controlled by the holder.

      • Unrevealed attributes are not (as I had thought) a way to choose to disclose/not disclose an entire referent (group of claims from a credential).

        • This is a desirable feature: Being asked for multiple types of credentials (ORs), any of which are suitable, with the expectation the holder holds (will respond with) only one of them.

          • Referents for "Person" Credential from three different jurisdictions (3 credential types), where any one person would ever only have 1 of the 3.

          • The AnonCreds Presentation Request syntax has no mechanism to make this kind of request.

            • Note: DIF Presentation Exchange does support this kind of syntax.

    • In the "Ask for 3 when I only have 1" issue, the holder is (evidently) able act unilaterally, assuming what the verifier intended:

      • A holder may respond to a presentation request with only a subset of the referents (claim groups) and the presentation will verify.

      • The verifier must then decide what to do – accept the presentation as meeting the business need or not.

        • E.g., ACA-Py was been coded to detect what the developer called a "bait and switch" by the holder – being very firm on the presentation matching the presentation request.

          • However, this approach rejects both the use of "unrevealed attributes", and the "one of many" use case.

    • Another example:

      • Verifier presentation request asks for a "Proof of Degree" based on a common schema.

      • The presentation may verify.

      • Is the credential that was used for the presentation from a trusted source?

      • Being able to scale requires this capability.

    • Issue:

      • AnonCreds stops at the cryptographic verification.

        • The verification wrapper around AnonCreds verification may go further.  Should that be part of the spec or not?

      • The protocol around AnonCreds may or may not have a "business verification" response.

      • How do we combine the two?

      • For AnonCreds v1.0 we clarify what is possible.

      • For AnonCreds v2.0 we adjust the design.

    • To Do:

      • Issue to talking about what AnonCreds verifies and what is left to the issuer to verify.

  • Dynamic Accumulator Revocation scheme

    • Proposal: To be presented two weeks from today.

  • Checkin: anoncreds-rs implementation progress, requests

    • Seems to be pretty stable right now – most effort is in using the implementation in various frameworks.

  • Open Discussion:

Future Calls

To Dos:

  • Issue #137 added regarding further investigation into what happens to the issuance data flow nonce(s) by Belsy – definition completed, to be added to the spec. @Stephen Curran 

  • Issue #140 should WQL be allowed in a Presentation Request?

    • WQL is supported currently in the Indy SDK, but not in the Aries Frameworks

    • Should it be in the specification?

    • If so, in what form. From @Sam Curren — don't call it WQL if we do include it – just describe it.

    • Not used and it is not clear there is a good reason to support it.

    • Complicates the specification and the implementation.

    • Decision:

      • Not supported in the specification – let's keep it out in this version

  • Revocation Interval

    • Approach to determine if the holder used an acceptable RevRegistry – see this Issue comment

    • Who calls the AnonCreds method to get the Revocation Registry from the ledger for verification

      • Verifier or AnonCreds?

    • To set "validation" to true/false based on the RevRegEntry timestamp in relation to the revocation interval?  Presentation 

    • Key points:

      • 1. an RevRegEntry is “current” from the time it is written, to the time of the next RevRegEntry

      • 2. “within the interval” is based on when a RevRegEntry is “current” (see 1.), not its timestamp.

      • 3. AnonCreds or the Verifier (calling AnonCreds) should calculate “within interval” (using 2.) and mark verification true if the RevRegEntry used by the Prover is within the interval, else false.

        • Dangers:

          • False-Negatives: If a strict "timestamp used is between from, to" and not based on when a RevReg is "current" (per 2.), we will get "not verified" incorrectly.

          • False-Positives: If we don't do any checking of the timestamp and the interval, the holder could incorrectly use an old RevRegEntry.

      • 4. General point: AnonCreds should return both a summary (true/false) and if false, additional data about why it was false.

    • Decision – add an optional `at_from_ts` set of entries, one per NRP, that AnonCreds can use for determining if the holder_ts is within the Presentation Request interval.

  • Backwards Compatibility

    • PRs in (#82, #105) that seem to change public data structures – ones that are handled outside of AnonCreds and/or by two or more participants (issuer, holder, verifier)

    • We want to retain compatibility with existing data – credentials that have been issued and the published AnonCreds objects on which they rely.

    • That extends to business logic – e.g. the handling of the objects not just by AnonCreds, AnonCreds Methods and Aries Frameworks, but also by business applications built on Aries.

    • Suggestion:

      • Include in the specification a statement about backward compatibility

        • Perhaps this is what Ankur had planned to do?

      • Formalize what data structures will be expected by AnonCreds

        • This is being done throughout the specification and verified against the current implementation.

      • As needed support sending and receiving data in "old" and "new" formats, but (for now) always sending "old" formats.

        • TBD if there are any such cases.

Action items