2023-05-01 AnonCreds v2.0 Working Group Meeting

Summary

• Reviewing the proposed data models for AnonCreds v2.0 - https://hackmd.io/ZlsnLoclSveePJOZljgMfA
• Revocation using zk-SAM
• Open Discussion

Recording of Call:  

Notices: 

This specification creating group operates under the Linux Foundation Community Specification License v1.0.

Meeting Attendees

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

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

Related Repositories:

• Mike Lodder's proposed Data Models: https://hackmd.io/ZlsnLoclSveePJOZljgMfA
• AnonCreds v2.0 Specification Repository: https://github.com/hyperledger/anoncreds-spec-v2/
• AnonCreds v1.0 Specification: https://hyperledger.github.io/anoncreds-spec/
• AnonCreds Methods Registry: https://hyperledger.github.io/anoncreds-methods-registry
• AnonCreds Rust Open Source Code: https://github.com/hyperledger/anoncreds-rs

Goals of the Working Group:

The goal of AnonCreds v2.0 is to retain and extend the privacy-preserving features of AnonCreds v1.0, while improving capabilities, performance, extensibility, and security.

Meeting Preliminaries:

• Welcome and Introductions
• Announcements:
  • AnonCreds Workshop presented by Hyperledger is planned for May 31, 2023, 8:00 Pacific / 17:00 Central Europe. Details to be shared.
  • I'll be talking at the Linux Foundation Open Source Summit, Metaverse Conference about Hyperledger AnonCreds and ZKPs.
• Updates to the Agenda?

Agenda

• Proposed data models discussion given what Mike Lodder has presented and documented here: https://hackmd.io/ZlsnLoclSveePJOZljgMfA
  • Issuing AnonCreds v1.0:
    • Schema – simple list of attribute names, schema name, version
      • Attribute type is dynamically implied by the data in the credential – string or integer
    • Credential Definition – a signing key for each attribute, an extra field that is the link secret
    • Credential
      • Raw and encoded claims
      • Signature is added
  • Issuing v2.0
    • From document – items:
      • Claims – Schema, Validators, Data
      • Credential Schema, Credential Definition 
      • Credential
    • Proposal that types are defined in the AnonCreds specification 
    • Claims Schema Repository
      • Name, ID, type, validators
    • Credential Schema Object:
      • Name, Description (should also have version?) 
      • Blindly Signed Claims Schema
        • Attribute name/ID from Claims Schema
      • Ordered List: Claims Schema
        • Attribute name/ID from Claims Schema, or
        • Attribute Name, ID, type, validators
    • Credential Definition Object
      • Keys necessary to sign credentials
        • Parameters per attribute – could be derived when using some signature schemes
      • ID of Schema Object
      • Revocation Registry – keys
    • Credential:
      • Claims
      • Signature
      • Revocation Registry Handle
      • Credential Definition ID
  • Signature Schemes
    • CL
    • BLS - doesn't support selective disclosure
    • BBS+ - IETF submitted version can be used
      • PQ unlikely – none known at this time.
    • PS - Mike, et. al (potentially including "S" in "PS") is taking this to IETF
      • Has a post-quantum version, but slower and bigger
        • Calculation for 5 claims – in the Credential Definition: Public Key 912 bytes, PQ version: 6KB, increasing linearly (6x bigger)
          • Proof: 300-400 bytes, PQ version: 24kb (50x bigger)
        • Could be fixed size 192b and then derive the per claim data attributes (tradeoff size vs. time)

Future Calls

• Collect some use case specific examples and continue the discussions:
  • Applying the data structures to a real use case or two
    • Take an existing AnonCreds Schema (maybe this) and Credential Definition (maybe this) and define what it would be using Mike's proposed data models.
      • Where would the data models exist, such as on ledger, in the AnonCreds specification?
  • What concrete uses other than link-secret is there for blinded data in a credential?

To Dos:

Action items