Verifier Algorithm

This page restates the APP v0.4.0 verifier flow as implementation-oriented pseudocode. The whitepaper remains authoritative.

Inputs

sealed_policy: signed and encrypted APP permission policy
execution_context: runtime identity, audience, trusted clock, requested capability, requested operation, request correlation ID, and replay state
approval_receipt: optional signed APP-Approval-1 receipt
capability_registry: verifier-controlled capability-to-operation mapping

Fail-Closed Flow

function verify_app_execution(sealed_policy, execution_context, approval_receipt):
  plaintext_policy = decrypt(sealed_policy)
  if decrypt failed:
    deny("policy_decryption_failed")

  if signature_invalid(plaintext_policy):
    deny("policy_signature_invalid")

  policy = parse_and_validate_required_fields(plaintext_policy)
  if invalid:
    deny("policy_invalid")

  if unsupported_policy_version(policy.policy_version):
    deny("policy_version_unsupported")

  if trusted_clock < policy.not_before:
    deny("policy_not_yet_valid")

  if trusted_clock > policy.expires_at:
    deny("policy_expired")

  if replay_protection_present(policy) and replay_seen(policy.nonce):
    deny("policy_replay")

  if policy.audience != execution_context.audience:
    deny("audience_mismatch")

  revocation = check_revocation(policy)
  if revocation is revoked or indeterminate:
    deny("policy_revoked_or_revocation_indeterminate")

  if policy.derivation_chain is present:
    if derivation_chain_invalid(policy):
      deny("derivation_chain_invalid")

  if approval_gate_applies(policy.approval_gate, execution_context):
    if approval_receipt is missing:
      if policy.approval_gate.mode == "async":
        suspend("approval_required")
      deny("approval_required")

    if approval_receipt_signature_invalid(approval_receipt):
      deny("approval_receipt_signature_invalid")

    if approval_receipt.policy_id != policy.policy_id:
      deny("approval_receipt_policy_mismatch")

    if challenge_binding_invalid(approval_receipt, execution_context):
      deny("approval_receipt_challenge_mismatch")

    if approval_receipt.decision != "approved":
      deny("approval_receipt_denied")

    if trusted_clock > approval_receipt.expires_at:
      deny("approval_receipt_expired")

    if replay_seen(approval_receipt.nonce):
      deny("approval_receipt_replay")

    if approver_not_trusted(policy.approval_gate, approval_receipt.approver_authority):
      deny("approval_receipt_untrusted_authority")

    if not subset(approval_receipt.approved_scope, policy.scope):
      deny("approval_receipt_scope_expansion")

  capabilities = resolve_capabilities(policy.scope, capability_registry)
  if resolution_failed:
    deny("capability_resolution_failed")

  execution_surface = construct_execution_surface(capabilities)
  if execution_surface_invalid:
    deny("execution_surface_invalid")

  if limits_invalid_or_exceeded(policy.limits, execution_context):
    deny("limits_invalid_or_exceeded")

  audit_decision(policy, execution_context, approval_receipt, "allow")
  allow(execution_surface)

Required Denial Behavior

Verifiers must deny when any required field is absent, cryptographic checks fail, trust roots are unavailable, revocation is indeterminate under the selected mode, derivation expands authority, approval receipts are invalid, or runtime context is missing.

Approval receipts do not create authority. They only unlock gated authority already declared in the sealed policy. Expanded authority requires a newly issued sealed policy.

Assets

Policy schema: schemas/app-permission-policy.schema.json
Approval challenge schema: schemas/approval-challenge.schema.json
Approval receipt schema: schemas/approval-receipt.schema.json
Approval receipt vectors: conformance/v0.4.0/approval-receipts.json