Anonymous Credentials is about protecting information that gets unrevealed for questionable reasons.
Due to that the Issues and the Verifier have to share a common understanding of what the Holder will declare e.g., “My age is above 21”. The Verifier and the Issuer may share the question “Is the age above 21?”. The Issues give this credential to the Holder. The Verifier gets this credential presented (on its age-request).
Technically multiple implementations exist. One naive one is
- Verifier sends question to Issuer
- Holder reveals information to Issuer
- Issuer check information against Verifier question
- Issuer encrypts result with the public key of the Verifier
- Issuer sends claimed proof credentials to the Holder
- Holder presents claimed credentials to the Verifier
For Ethereum one implementation is https://zokrates.github.io/