Send cinematic cards
from any AI agent

ABT-C as an orthogonal layer

ABT-C v2 is not a replacement for AP2, UCP MCP, or the ACP REST API. It is a cryptographic layer that sits beneath them — activating conditionally when both parties support it.

Standard path — AP2 IntentMandate, UCP MCP create_checkout_session, and ACP REST /checkout all route to the standard Stripe checkout by default. No ABT overhead.

ABT-C path — When the consumer's device includes abt_consumer_pubkey or the request carries abt_origin, the same endpoints route to /api/agent/v2/checkout. The consumer's PII never crosses the network in plaintext.

What it adds — Per-tier key derivation, registry witness mode, retention-enforced PII destruction. The three structural properties described at sidratnam.com/abt-c.

Verification

After receiving an ABT response, verify the envelope signature against the JWKS public key. The signature is permanent (it does not expire). Decryption of the envelope contents requires calling decrypt_envelope before the retention period expires; after expiry, decryption fails with error code -32005 and the data is unrecoverable.

Discovery files for ABT

CinematicCard is live on ABT-C v2 with 50 verified production scenarios. Last verified: 2026-05-11. Covered by US Provisional Application No. 64/056,353.

ABT-C v2 — Consumer-Side Key Escrow

The correct architecture for privacy-preserving agent commerce. PII never leaves the consumer's device in plaintext — not even to reach the merchant API.

In earlier ABT versions, the consumer co-signed an envelope after the merchant had already received their data. ABT-C v2 inverts this: the consumer generates the encryption key before making the request, encrypts all PII client-side via HKDF, and deposits the key in a neutral escrow at sidratnam.com. The merchant only ever receives ciphertext. To fulfil the order, the merchant proves its identity via a short-lived JWT and collects the key — the escrow logs the handoff permanently.

How it works (5 steps)

Request — ABT-C v2 checkout

{
  "abt_version": "2",
  "tx_id": "<uuid — generated by consumer>",
  "callback_url": "https://sidratnam.com/api/txn/<tx_id>/key",
  "encrypted_fields": {
    /* each field independently AES-256-GCM encrypted with per-tx key */
    "recipient_email": { "ciphertext": "...", "iv": "...", "tag": "..." },
    "sender_email":    { "ciphertext": "...", "iv": "...", "tag": "..." },
    "recipient_name":  { "ciphertext": "...", "iv": "...", "tag": "..." },
    "message":         { "ciphertext": "...", "iv": "...", "tag": "..." }
  },
  "plaintext_fields": {
    "theme": "elegant",
    "music": "piano",
    "promo_code": "..."
  },
  "retention_context": { "retention_seconds": 2592000, "policy_version": "20260502-001" }
}

Response — encrypted back to consumer

/* outer wrapper */
{ "encrypted_response": { "ciphertext": "...", "iv": "...", "tag": "..." } }

/* decrypted payload */
{
  "ok": true,
  "order_id": "a1b2c3",
  "card_url": "https://cinematiccard.com/c/a1b2c3.html",
  "status": "generated",          // or "pending_payment"
  "abt_origin": "abt-c",
  "schema_version": "abt-c-v2",
  "envelope_id": "<uuid>"          // 18-tier envelope stored in vault
}

Privacy guarantees

Key derivation (consumer side)

// Node.js
const perTxKey = crypto.hkdfSync(
  'sha256',
  masterKeyBytes,   // 32-byte consumer master secret
  txId,             // UUID — unique per transaction
  JSON.stringify({ merchant_domain: 'cinematiccard.com', expiry_ts, policy_version }),
  32
);
// Re-derive with same inputs to re-decrypt any response

Discovery: /.well-known/ucp — UCP manifest with abt_checkout_url pointing to this endpoint. Compliance: GET https://sidratnam.com/api/abt/v1/registry/compliance/cinematiccard.com

No key required to start

All GET endpoints and POST /quote have no auth requirement. POST /checkout works without a key but has stricter rate limits.

X-Agent-Key — optional, recommended

Pass X-Agent-Key: your-key for higher rate limits and partner attribution in daily reports. Request: [email protected]

# Safe retries — same key returns original response for 24h
-H "Idempotency-Key: your-stable-order-ref"
# or in body:
"agent": { "orderReference": "your-stable-order-ref" }