GHSA-6698-mhxx-r84g

### Summary

The revocation scheme that is part of the Ursa CL-Signatures implementations has a flaw that could impact the privacy guarantees defined by the AnonCreds verifiable credential model. Notably, a malicious verifier may be able to generate a unique identifier for a holder providing a verifiable presentation that includes a Non-Revocation proof.

### Details

The revocation scheme that is part of the Ursa CL-Signatures implementations has a flaw that could impact the privacy guarantees defined by the AnonCreds verifiable credential model, potentially allowing a malicious verifier to generate a unique identifier for a holder that provides a verifiable presentation that includes a Non-Revocation proof.

The flaws affects all CL-Signature versions published from the [Hyperledger Ursa] repository to the [Ursa Rust Crate], and is fixed in all versions published from the [Hyperledger AnonCreds CL-Signatures] repository to the [AnonCreds CL-Signatures Rust Crate].

The addressing the flaw requires updating AnonCreds holder software (such as mobile wallets) to a corrected CL-Signature implementation, such as the [AnonCreds CL Signatures Rust Crate]. Verifying presentations from corrected holders requires a updating the verifier software to a corrected CL-Signatures implementation. An updated verifier based on AnonCreds CL-Signatures can verify presentations from holders built on either the flawed Ursa CL-Signature implementation or a corrected CL-Signature implementation

[Hyperledger Ursa]: https://github.com/hyperledger-archives/ursa [Ursa Rust Crate]: https://crates.io/crates/ursa [Hyperledger AnonCreds CL-Signatures]: https://github.com/hyperledger/anoncreds-clsignatures-rs [AnonCreds CL-Signatures Rust Crate]: https://crates.io/crates/anoncreds-clsignatures

The flaw occurs as a result of generating a verifiable presentation that includes a Non-Revocation proof from a flawed implementation.

### Impact The impact of the flaw is that a malicious verifier may be able to determine a unique identifier for a holder presenting a Non-Revocation proof.

### Mitigation

Upgrade libraries/holder applications that generate AnonCreds verifiable presentations using the [Ursa Rust Crate] to any version of the [AnonCreds CL-Signatures Rust Crate].