Verifiable Data Registry

The core function of a VDR is to resolve a DID to its corresponding DID Document. This document contains the public keys, service endpoints, and verification methods necessary to establish cryptographic trust. Unlike a traditional DNS lookup, this resolution does not rely on a single centralized authority.

• Method-Specific Identifiers: DIDs are prefixed with a method (e.g., did:web:, did:key:) that defines how resolution occurs.
• DID Document: A JSON-LD file containing cryptographic material, such as Ed25519VerificationKey2020.
• Trust Anchor: The VDR acts as the source of truth for binding a DID to its current keys.

A VDR maintains a revocation registry or status list to signal whether a previously issued Verifiable Credential (VC) is still valid. This is critical for audit trails, as it allows a verifier to instantly check if an auditor's certification has been revoked without contacting the issuer directly.

• StatusList2021: A bitstring-based mechanism for publishing credential statuses efficiently.
• Revocation vs. Suspension: The registry must distinguish between permanently revoked and temporarily suspended credentials.
• Privacy Preservation: Status checks should not leak which specific credential is being verified.

To achieve non-repudiation, a VDR often anchors a Merkle root of its transaction log to a public blockchain. This process, known as blockchain anchoring, provides an external, globally verifiable timestamp that proves the registry data existed in a specific state at a specific time.

• Merkle Tree Accumulator: Aggregates multiple registry operations into a single root hash.
• External Witness: The public blockchain acts as an impartial witness to the registry's history.
• Tamper-Evident: Any alteration to the registry history invalidates the anchored hash.

A robust VDR supports cryptographic agility by allowing controllers to rotate signing keys without losing their identifier. The registry must securely manage the transition from a compromised or expired key to a new one, maintaining the continuity of the audit trail.

• Forward Secrecy: Compromise of a current key does not expose past signed logs.
• Recovery Mechanisms: Social recovery or multi-signature schemes can be registered to regain control of a DID.
• verificationMethod Update: The DID Document is updated to list the new active public key.

The VDR must support multiple DID Methods to ensure interoperability across different ecosystems. Whether resolving a did:web for a corporate identity or a did:key for an ephemeral agent, the registry provides a unified interface for verification.

• DID Core Architecture: Conforms to the W3C DID Core specification for universal resolvability.
• Method Drivers: Pluggable modules that handle the specific read/write logic for each DID method.
• Cross-Registry Communication: Enables verification of credentials issued by entities on different underlying networks.

Advanced VDRs support cryptographic schemes like BBS+ Signatures that enable selective disclosure. A holder can derive a proof from a VC that reveals only the specific claims required by a verifier (e.g., proving age > 18 without revealing birth date), while the VDR still validates the signature's integrity.

• Zero-Knowledge Proofs (ZKPs): Allows verification of a statement without revealing the underlying data.
• Unlinkability: Prevents verifiers from correlating presentation proofs.
• Schema Validation: The registry can enforce the structure of claims without seeing the raw data.