The Agentity Protocol implements defense-in-depth across six security mechanisms:

Every agent has an Ed25519 keypair. All identity documents (AIDs) are self-signed. Each HTTP request carries:

Agentity-Token: <base64url(AID_json)>.<base64url(signature)>
Agentity-Nonce: <uuid-v4>
Agentity-Timestamp: <ISO-8601>

The signature covers:

SHA-256(did + nonce + timestamp + method + path + body_hash)

Verification steps:

1. Decode token → AID JSON + signature
2. Extract public key from AID
3. Verify Ed25519 signature on the signed payload
4. Check AID not expired
5. Check status via registry (active)
6. Validate scopes against provider manifest

• Each request includes a UUID v4 nonce
• Timestamps must be within ±300 seconds of server time
• Nonces are tracked server-side (in-memory Set or Redis) with TTL matching the tolerance window
• Replayed nonces: HTTP 403

When a key is rotated:

agentity_sdk/
  AgentKeyPair.rotate(previous_aid, ttl_days=90)

• New Ed25519 keypair generated
• New AID gets version = previous.version + 1
• previousAid field links to old AID
• Old AID status → expired
• Audit log records the rotation

Rotate proactively on a schedule or when a compromise is suspected.

Root owner (human)         delegationDepth: 0
  └─ Agent A               delegationDepth: 1, parent: root
       └─ Agent B          delegationDepth: 2, parent: A
            └─ Agent C     delegationDepth: 3, parent: B

Rules:

• Max 10 levels of delegation
• Child scopes must be a subset of parent scopes (no scope escalation)
• Revoking a parent cascades to all descendants
• Each AID's parent field contains the parent's DID

Human ownership is verified via OAuth2:

1. User logs in via Google/GitHub
2. Agentity creates a did:agentity:human:{fingerprint} from the provider's user ID
3. Session token binds the owner DID
4. Registry accepts registration only with verified owner_did
5. API: GET /auth/login/google, GET /auth/callback/google, POST /register

Apple and Microsoft providers are also supported but require client credentials.

• Redis-backed per-DID
• Default: 100 requests / 60 second window
• Response header: X-RateLimit-Remaining
• HTTP 429 when exhausted

Every registry event (create, revoke, rotate) is logged with:

• HMAC-SHA256 signature
• DID, event type, timestamp, actor, reason
• Verifiable via GET /audit/{did}/verify