Suspended Credential

A Suspended Credential is a status flag applied to a Verifiable Credential (VC) or attestation, indicating it is no longer valid. This is a critical feature of decentralized identity (DID) systems, allowing the issuer to revoke trust without needing to modify the underlying credential data on-chain. Its primary purposes are:

• Maintain Issuer Sovereignty: The entity that issued the credential retains control over its lifecycle.
• Ensure Data Freshness: Signals to verifiers that the information may be outdated or incorrect.
• Compliance & Security: Allows for rapid response to credential compromise, user request, or regulatory requirement.

Suspension is typically implemented via a revocation registry, a dedicated on-chain or off-chain data structure that tracks the status of issued credentials. Key standards defining this pattern include:

• W3C Verifiable Credentials Data Model: The foundational standard, with recommendations for status mechanisms like revocation lists.
• Hyperledger AnonCreds: Uses cryptographic accumulators and revocation registries for efficient, privacy-preserving status checks.
• W3C Verifiable Credential Status List 2021: A specific, interoperable standard for encoding a bitstring status list (a revocation list) within a credential itself.

While often used interchangeably, suspension and revocation can have nuanced differences in implementation:

• Suspension: Often implies a temporary invalidation. The credential may be reinstated later, making it a reversible action.
• Revocation: Typically implies a permanent invalidation. The credential is considered permanently untrustworthy. In practice, most systems use a single status mechanism (a revocation registry) to handle both states, with the permanence determined by issuer policy rather than technical implementation.

For a verifier, checking credential status is a mandatory step. The process involves:

1. Parse Credential: Extract the status method (e.g., a URL to a revocation list) from the credential's credentialStatus field.
2. Query Registry: Fetch the current status information from the specified revocation registry.
3. Verify Proof: Cryptographically verify that the credential's unique identifier (e.g., credential index) is not present on the suspension/revocation list. This check ensures the credential is currently valid at the time of verification, which is essential for real-world trust.

Suspended credentials are vital for dynamic, real-world attestations:

• Employment & Licensing: A university suspends a diploma credential if a degree is rescinded.
• Financial KYC/AML: A bank suspends a Proof-of-Address credential if the customer moves.
• Access Control: A DAO suspends a membership credential for a member who violated governance rules.
• Supply Chain: A certification body suspends an organic produce attestation for a farm failing an audit. Each case demonstrates the need for issuers to update the trustworthiness of claims over time.

Designing a suspension system involves key trade-offs:

• Privacy: Naive implementations can leak information. Zero-Knowledge Proofs (ZKPs) and cryptographic accumulators allow verifiers to check status without revealing which specific credential is being verified.
• Performance & Cost: On-chain updates to a revocation registry incur gas fees. Off-chain registries with on-chain anchoring (e.g., using IPFS or Ceramic Network) are common compromises.
• Availability: The revocation registry must be highly available for verifiers to query. Decentralized storage or issuer-hosted endpoints with high uptime are critical.

Suspension is a trust-minimized revocation mechanism. Instead of deleting a key, a smart contract or protocol governance places it on a denylist. The credential's public key remains on the blockchain, but any transaction signed by its corresponding private key is rejected by network validators. This is often implemented via an access control list (ACL) or a suspension registry.

Suspension is critical for responding to security incidents and enforcing compliance.

• Incident Response: Immediately block a compromised private key from authorizing malicious transactions.
• Regulatory Compliance: Enforce sanctions or legal orders by freezing assets associated with a specific address.
• Key Rotation: Gracefully deprecate old administrative keys during a multi-sig wallet upgrade.
• DAO Governance: Temporarily suspend a member's voting power pending an investigation.

Implementation varies by protocol:

• Smart Contract Logic: Functions like suspend(address _account) update a mapping (mapping(address => bool) public isSuspended). A modifier checks this state before executing sensitive functions.
• Validator Enforcement: In some systems, validators or relayers check a centralized or decentralized registry before including a transaction in a block.
• Signature Verification: The verification algorithm itself can be designed to fail for signatures from keys on a known suspension Merkle tree.

Suspension mechanisms introduce a centralization vector. The authority with suspension power (e.g., a multi-sig council, DAO, or off-chain entity) becomes a single point of failure/censorship. The trade-off is between security agility and permissionlessness. Overuse can undermine the credibly neutral properties of the system. Designs aim to make suspension transparent, auditable, and governed by clear rules.

Suspension is distinct from deletion or key invalidation.

• Suspension: The public key/address remains immutably on-chain in a suspended state. History is preserved.
• Deletion/Invalidation: The cryptographic key material is rendered permanently unusable (e.g., destroying a private key). On-chain, this might involve migrating assets to a new address, making the old one dormant.

Suspension is reversible; deletion is typically not.

Consider an ERC-20 token with snapshot capabilities for voting. The contract owner (or a DAO) can call function suspendVoter(address voter) to add them to a suspendedVoters mapping. The snapshot() or delegate() function would then include a require statement: require(!suspendedVoters[msg.sender], "Voter suspended");. This prevents the suspended address from participating in governance without affecting its token balance.