AnonCreds (Anonymous Credentials)

Holders can reveal only the minimum necessary information from a credential while keeping all other attributes hidden. Beyond simple attribute revelation, AnonCreds supports predicate proofs—cryptographic demonstrations that an attribute satisfies a condition (greater than, less than, within range) without disclosing the actual value.

• Attribute disclosure: Reveal only expiry_date while hiding name and address
• Zero-knowledge predicates: Prove age > 21 without revealing exact birthdate
• Interval proofs: Demonstrate a value falls within a specific range
• Set membership: Prove an attribute belongs to an allowed set without identifying which element

Every presentation generated from an AnonCred credential uses a freshly generated proof with a unique cryptographic nonce. This ensures that even if the same credential is presented to the same verifier multiple times, the presentations cannot be linked together. This property is known as multi-show unlinkability.

• Unique proofs per presentation: Each interaction produces cryptographically distinct evidence
• No common identifier: Unlike X.509 certificates, no serial number or fingerprint is exposed
• Verifier unlinkability: Two verifiers cannot collude to correlate a user's activity
• Protection against tracking: Prevents the creation of a behavioral profile across service providers

AnonCreds credentials are defined through a schema that specifies the list of attribute names and their types. An issuer then publishes a credential definition on a Verifiable Data Registry, which includes the cryptographic public key material and revocation registry reference. This layered architecture separates data modeling from cryptographic instantiation.

• Schema: Declares attribute names (e.g., given_name, family_name, date_of_birth)
• Credential Definition: Binds the schema to the issuer's public CL signing key
• Verifiable Data Registry: Stores schemas, credential definitions, and revocation registries immutably
• Versioning: Schemas can be versioned to support credential evolution without breaking existing holders

AnonCreds implements revocation using cryptographic accumulators rather than public certificate revocation lists. A holder proves their credential has not been revoked by demonstrating membership in the accumulator without revealing which specific credential they hold. This preserves unlinkability even during revocation checks.

• Accumulator-based: Uses dynamic accumulators that support efficient membership and non-membership proofs
• No correlation: Revocation check does not expose a unique credential identifier
• Revocation Registry: An append-only data structure published to the Verifiable Data Registry
• Witness updates: Holders periodically update their witness to reflect the latest accumulator state

Every AnonCred credential is cryptographically bound to a link secret—a blinding factor known only to the holder. This secret is embedded in the credential during issuance via a blind signing protocol and is proven during presentation without being revealed. The link secret prevents credential sharing and enables proving that multiple credentials belong to the same holder without identifying them.

• Anti-sharing mechanism: Makes credential transfer practically infeasible
• Cross-credential binding: Prove ownership of multiple credentials simultaneously
• Blind issuance: Issuer signs attributes without learning the link secret value
• Holder binding: Ensures only the original recipient can use the credential

A pairing-based, multi-message digital signature scheme that enables selective disclosure and zero-knowledge proofs. Unlike Camenisch-Lysyanskaya signatures used in AnonCreds v1, BBS+ allows a holder to derive a single proof that hides specific signed attributes while proving possession of others. This scheme is the cryptographic backbone of the W3C Verifiable Credential Data Integrity suite and is being integrated into AnonCreds v2 for broader interoperability.

The ability of a credential holder to reveal only specific attributes from a verifiable credential to a verifier. In AnonCreds, this is achieved through zero-knowledge proofs that cryptographically prove a subset of claims (e.g., 'age > 21') without exposing the raw data (e.g., exact birthdate). This minimizes unnecessary data exposure and is a core requirement of GDPR data minimization principles.

A cryptographically secure data structure that records the revocation status of verifiable credentials without revealing underlying data. AnonCreds uses cryptographic accumulators to allow a holder to generate a non-revocation proof demonstrating their credential has not been revoked, without the verifier needing to scan a list or contact the issuer. This preserves unlinkability even during status checks.

A signed aggregation of one or more verifiable credentials, assembled by a holder to share specific claims with a verifier. AnonCreds presentations are constructed using zero-knowledge proofs that combine multiple credentials into a single, tamper-proof proof. The verifier learns only what the holder explicitly discloses, with no correlatable identifier linking presentations across different sessions.

A cryptographic method allowing one party to prove to another that a statement is true without revealing any information beyond the validity of the statement itself. AnonCreds leverages ZKPs to enable predicate proofs (e.g., 'credit score > 700') and attribute hiding while maintaining cryptographic verifiability. This is the mechanism that prevents verifiers and issuers from colluding to correlate user activity.

A globally unique persistent identifier that does not require a centralized registration authority. AnonCreds are typically bound to a DID as the subject identifier, but the credential's schema and revocation registry are also anchored to DIDs on a Verifiable Data Registry. This decoupling from traditional PKI enables portable, self-sovereign identity architectures.