Ursa is a cryptographic library for use with blockchains. The revocation schema 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, allowing a malicious holder of a revoked credential to generate a valid Non-Revocation Proof for that credential as part of an AnonCreds presentation. A verifier may verify a credential from a holder as being "not revoked" when in fact, the holder's credential has been revoked. Ursa has moved to end-of-life status and no fix is expected.
Affected: crates.io: ursa, crates.io: anoncreds-clsignatures
### Summary
The revocation schema 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, allowing a malicious holder of a revoked credential to generate a valid Non-Revocation Proof for that credential as part of an AnonCreds presentation.
### Details
The revocation schema that is part of the Ursa CL-Signatures implementation has a flaw that could impact the privacy guarantees defined by the AnonCreds verifiable credential model, allowing a malicious holder of a revoked credential to generate a valid Non-Revocation Proof for that credential as part of an AnonCreds presentation.
The flaw exists in all CL-Signature versions published from the [Hyperledger Ursa] repository to the [Ursa Rust Crate], and are fixed in all versions published from the [Hyperledger AnonCreds CL-Signatures] repository to the [AnonCreds CL-Signatures Rust Crate].
To exploit the flaw, a holder must update their wallet (agent) software, replacing the Hyperledger Ursa or AnonCreds CL-Signatures library that generates the proof of non-revocation. This may involve, for example, altering an iOS or Android application published in the respective app stores. A mitigation for this flaw is to use the application attestation capabilities (such as the Android "[SafetyNet Attestation API]") offered by the app store vendors to (for example) "help determine whether your servers are interacting with your genu…