Zero-Knowledge Proof of Non-Revocation

A core application where ZK-NR proves a credential (e.g., a government ID or membership) is valid and has not been revoked by the issuer, without revealing the credential's details. This is foundational for self-sovereign identity systems like W3C Verifiable Credentials.

• Example: Proving you are over 18 without showing your birth date.
• Protocols: Used in zk-SNARKs or zk-STARKs based identity frameworks.

Ensures a user can cast a single, valid vote without revealing their identity or voting history, while preventing double-spending of voting rights. ZK-NR proves membership in a voter roll and that the voting credential has not been revoked.

• Mechanism: Combines with anonymous credentials and nullifiers.
• Use Case: DAO governance, shareholder voting, and private elections.

Allows users to prove eligibility for financial services or token distributions based on undisclosed criteria, while ensuring revoked or sybil addresses are excluded. This prevents fraud and preserves user privacy.

• Application: Claiming an airdrop by proving ownership of a non-revoked credential from a specific blockchain snapshot.
• Benefit: Enables selective disclosure and compliance without full KYC exposure.

Grants access to physical or digital resources by proving possession of a valid, non-revoked access pass. The resource provider verifies the proof without learning the user's specific identity or pass details.

• Examples: Accessing a private club, subscribing to a premium service, or entering a token-gated online community.
• Technology: Often implemented using zk-SNARKs for efficient verification.

Facilitates secure asset or message transfer between blockchains by proving the sender holds a valid, non-revoked state on the source chain. This enhances security and privacy for cross-chain operations.

• Function: Acts as a light client proof, verifying membership in a Merkle tree of valid accounts.
• Benefit: Reduces trust assumptions in bridge validators and minimizes data leakage.

Enables entities to prove compliance with regulations (e.g., sanctions lists, accredited investor status) to a verifier or auditor using a zero-knowledge proof, without exposing the underlying sensitive data or the entire user base.

• Key Concept: Selective Auditability. A regulator can be given a key to verify proofs without seeing individual user data.
• Advantage: Balances regulatory requirements with user privacy.

ZKPoNRs typically rely on accumulator schemes like RSA accumulators or Merkle trees. A trusted issuer maintains a public accumulator representing all revoked credentials. To prove non-revocation, the prover generates a zero-knowledge proof demonstrating that their secret credential is not a member of this revocation set, using a witness (e.g., a non-membership proof for the accumulator) without revealing the credential.

This technology enables selective disclosure, allowing users to prove specific claims (e.g., 'I am over 18' or 'my diploma is valid') without exposing their full identity. It shifts the trust model from revealing raw data to verifying cryptographic assertions, balancing user privacy with a verifier's need for assurance. This is crucial for self-sovereign identity (SSI) and private credential systems.

A critical security consideration is the trust placed in the revocation authority (issuer). This entity has the power to revoke any credential. Systems must ensure:

• The authority cannot falsely prove non-revocation.
• Revocation updates are timely and propagated to verifiers.
• The authority's operations are transparent or decentralized to mitigate single points of failure and censorship.

Key implementation risks include:

• Witness Update Complexity: Users must frequently update their non-revocation witness, which can be computationally heavy for large revocation sets.
• Linkability: Poorly designed protocols may allow verifiers to link multiple proofs back to the same user, breaking privacy.
• Soundness Bugs: Flaws in the cryptographic circuit or proof system could allow a prover to falsely claim non-revocation.

ZKPoNR is the backbone of anonymous credential systems like Coconut or idemix. For example, a university issues a cryptographically signed credential. A graduate can later prove to an employer that they hold a valid, non-revoked degree from that university, without revealing their student ID number or the credential's unique signature, preserving privacy.

On-chain, ZKPoNRs enable private access to DeFi pools, DAO voting, or token-gated content. The proof is verified by a smart contract. Scalability challenges involve:

• Gas Costs: On-chain verification of complex ZK proofs can be expensive.
• Data Availability: Ensuring verifiers can access the current state of the revocation accumulator (e.g., via oracles or intermediate state roots).

A cryptographic method where one party (the prover) can prove to another party (the verifier) that a statement is true, without revealing any information beyond the validity of the statement itself. This is the foundational technology enabling proofs of non-revocation.

• Types: zk-SNARKs, zk-STARKs, Bulletproofs.
• Core Properties: Completeness, Soundness, Zero-Knowledge.

A cryptographically secured, append-only data structure (often a Merkle tree or accumulator) that maintains a list of revoked credential identifiers. To prove non-revocation, a prover demonstrates their credential's unique identifier is not present in this registry.

• On-Chain vs. Off-Chain: Can be stored on a blockchain for public auditability or managed by a trusted issuer.
• Efficiency: Sparse Merkle trees allow for efficient proofs of non-membership.

The ability to reveal only specific, necessary attributes from a credential while keeping all others hidden. Zero-Knowledge Proof of Non-Revocation is often combined with selective disclosure to prove a credential is both valid and unrevoked, without exposing its full contents.

• Example: Proving you are over 21 from a driver's license without revealing your birth date, name, or address, and simultaneously proving the license is not revoked.

A portable, verifiable identifier controlled by the user, not a central authority. DIDs are often the subject of verifiable credentials that require non-revocation proofs. The DID document contains public keys used for authentication and proof presentation.

• W3C Standard: A key component of the Self-Sovereign Identity (SSI) model.
• Linkage: A ZK proof of non-revocation can attest that the DID controlling a credential is still in good standing.

A tamper-evident digital credential whose issuer can be cryptographically verified. Non-revocation proofs are a critical mechanism for maintaining the ongoing validity of a VC after issuance.

• Structure: Contains claims, metadata, and proofs.
• Lifecycle: Issuance → Holding → Presentation → Verification (which includes revocation check).

A cryptographic primitive that can represent a large set of elements with a single, short value. Used in some revocation schemes as an alternative to Merkle trees. To prove non-revocation, one shows a witness that their credential is accumulated in the current set.

• Types: RSA Accumulators, Bilinear Map Accumulators.
• Advantage: Allows for constant-size witnesses and updates independent of set size.