Ursa CL-Signatures Revocation allows verifiers to generate unique identifiers for holders

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

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.