Native library reference. Extended CLI examples use jacs-compat. This source reference can include unreleased changes; see the package guide for installation and MCP profiles for available tools.

DNS Trust Anchoring

DNS can associate a public-key fingerprint with a domain. It does not by itself prove the identity of a person or organization, authorize an action, or enroll an agent in your trust store. The current native resolver's configuration and verifier coverage are distinct from portable CLI/MCP explicit-key verification and A2A card policy.

Fingerprints and routing

Records at _v1.agent.jacs.<domain> use:

v=jacs; jacs_agent_id=<agent-uuid>; alg=SHA-256; enc=base64; jac_public_key_hash=<raw-key-digest>

jac_public_key_hash encodes SHA-256 of raw public-key bytes. It is not the signed envelope's historical publicKeyHash string or a hash of its PEM armor. An optional HTTPS uri points to supported discovery JSON; otherwise the resolver uses https://<domain>/.well-known/jacs-pubkey.json.

A signed v2 agentDomain is authenticated only after the envelope verifies. Before then it is a routing hint. Network requests require explicit capability opt-in, bounded secure transport and key/reference checks. Existing identity conflicts or distrust are not overridden by discovering a new key.

DNSSEC and local trust

Strict lookup requires the validating resolver to return a Secure DNSSEC proof. A remote server's AD bit is not accepted as proof on its own. The zone must be signed and its DS delegation correctly published. Non-strict lookup has no equivalent cryptographic DNS authentication.

DNSSEC protects records in transit; it does not prevent a compromised or authorized DNS administrator from publishing a new key. Short TTLs do not fix that threat. Keep application identity pins, authorization and revocation policy separate from discovery. HTTPS and DNSSEC support also do not make the entire channel post-quantum secure.

Rotation limits

Agent-specific lookup selects the relevant agent's records and matches a candidate's raw digest. Multiple agents and overlapping keys can coexist; conflicting locations for the same agent and fingerprint are rejected. Publishing an old key does not certify that it remains authorized. JACS does not automatically publish DNS changes, maintain a transparency history, or provide a DNS revocation feed. Plan overlap around actual caches and retained signed documents, and retain exact historical-version key endpoints as needed.

See DNS publication, key rotation, and the current key-discovery guide.