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Actors

MPCP defines several actor types that participate in machine payment flows.

Fleet Operator

Owns and manages the autonomous fleet (vehicles, robots, agents).

Responsibilities:

  • Defines vehicle payment policies
  • Sets spending limits
  • Restricts allowed vendors and locations
  • Issues PolicyGrant artifacts

Examples: Robotaxi fleet, delivery fleet, autonomous logistics fleet.

Vehicle Wallet (Machine Wallet)

Resides in each machine (EV, robot, IoT device) and enforces MPCP constraints.

Responsibilities:

  • Enforces policy constraints
  • Manages charging/payment budgets
  • Issues SignedBudgetAuthorization and SignedPaymentAuthorization
  • Executes settlement transactions

The wallet is the MPCP actor that signs SignedBudgetAuthorization and SignedPaymentAuthorization.

Note on Actor Identity: The actorId field in SBA artifacts is self-reported by the wallet. Production deployments SHOULD establish actor attestation via device key binding (e.g., a hardware-backed key whose public key is registered with the fleet operator). Without attestation, actorId cannot be cryptographically verified and is informational only.

AI Agent

An AI agent acting under human authorization, using MPCP to bound its spending authority.

Receives: PolicyGrant signed by a human principal (DID key)

Responsibilities:

  • Receives a PolicyGrant from a human principal (DID-signed) and acts as its spending subject
  • Acts as session authority — creates and signs SBAs (typically with TRIP scope)
  • Acts as payment decision service — enforces allowedPurposes and signs SPAs
  • Maintains cumulative spend counter across all sessions in the trip/project
  • SHOULD check revocationEndpoint before signing each SPA (agents are online by design)

Contrast with Vehicle Wallet:

Vehicle Wallet AI Agent
Policy authority Fleet operator Human (DID)
Connectivity Offline-capable Online by design
Revocation Not applicable SHOULD check before each payment
Budget scope SESSION / DAY TRIP (multi-day)

Examples: Travel booking agent, subscription manager, event budget agent.

The actorId field in SBA artifacts is used for agent identity (e.g. "ai-trip-planner-v2"). Agent attestation follows the same key binding recommendations as vehicle wallets.

Service Provider

The entity that receives payment for a service (parking, charging, tolls).

Responsibilities:

  • Requests payment authorization
  • Verifies MPCP artifact chain
  • Provides or denies service based on verification

Examples: Charging network operator, parking operator, toll system.

Route / Dispatch System

(Optional) Determines routing and service requirements.

Responsibilities:

  • Determines charging/parking locations along route
  • Identifies approved service networks
  • Provides trip metadata to the vehicle

May influence PolicyGrant constraints.

MPCP Verifier

Validates the full authorization chain.

Verification may occur:

  • Inside the service provider backend
  • Inside a dedicated MPCP verification service
  • During post-transaction auditing

Settlement Rail

Executes the actual payment.

Examples: XRPL + RLUSD, EVM stablecoins, Stripe, hosted providers.

MPCP does not replace settlement systems—it controls authorization above them.

See Also