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SECURITY.md

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IntentFence security model

Trust boundaries

  • IntentFence treats all caller-provided identity, proofs, prices, and constraints as declarations unless an explicit external verifier is named.
  • The receipt signing key is separate from the USDC recipient wallet and is stored only as a production secret.
  • IntentFence never requests or receives a payer wallet seed phrase or private key.
  • x402 payment settlement and IntentFence receipt signing are independent signals.

Controls in 0.7

  • Bounded request sizes for preflight, MCP, A2A, and quote-assessment inputs.
  • Strict field bounds and finite-number validation.
  • MCP Origin validation, protocol-version handling, and stateless transport.
  • ES256 algorithm and key-id pinning; five-minute quote-assessment receipts and 24-hour declared-policy receipts.
  • Public offline-verifiable JWKS plus a bounded verification endpoint.
  • Failed validation or signing returns an HTTP error before x402 settlement.
  • x402 quote assessments accept a base64 payment_required value no larger than 16 KiB and validate it as the exact caller-observed x402 v2 challenge.
  • The official x402 schema is applied before classification. Canonical Base USDC must declare the expected USD Coin / 2 EIP-712 domain; Permit2, unknown transfer metadata, and active or unknown extensions cannot receive safe_to_proceed without review.
  • A safe_to_proceed result requires an explicit allowed_payees entry that matches the quote. If the list is omitted, the result is needs_review.
  • Every advertised payment option must pass every automatic check. Mixed compliant and unsafe option sets fail closed.
  • After facilitator verification, D1 atomically reserves each EIP-3009 payer + nonce authorization before assessment signing. Concurrent replay is rejected and failed or unsettled attempts release the reservation.
  • The service never fetches or pays the target. It signs SHA-256 bindings for the full target URL and exact supplied payment requirement, then settles the 0.005 USDC IntentFence assessment fee.

Not yet provided

The service does not verify real-world identity, independently validate authorization grants, prove target ownership or delivery, establish that the caller received the challenge from the claimed target, or guarantee that a downstream service enforced a decision. A quote assessment is a signed evaluation of caller-supplied challenge bytes, not a merchant certification. Callers should obtain the challenge immediately before assessment and compare the current target challenge before signing a downstream payment. Those are separate high-assurance integrations.