Chain of Provenance for Authority (Delegation)

The following use case is framed in terms of verifiable credentials. It's possible that we could use a different container for ACDC. Therefore, read "verifiable credential" as "whatever container mechanism we settle on for ACDC."

The national headquarters of Ur Wheelz (a car rental company) issues a verifiable credential, C1, to its regional office in Houston, authorizing Ur Wheelz Houston to rent, maintain, sell, drive, and delegate driving privileges to customers, for certain cars owned by the national company.

Alice rents a car from Ur Wheelz Houston. Ur Wheelz Houston issues a driving privileges credential, C2, to Alice. C2 gives Alice the privilege to drive the car on a particular week, within the state of Texas, and to further delegate that privilege. Alice uses her C2 credential to prove to the car (which is a fancy future car that acts as verifier) that she is an authorized driver; this is what unlocks the door.

Alice gets pulled over for speeding on Wednesday and uses C2 to prove to the police that she is the authorized driver of the car.

On Thursday night Alice goes to a fancy restaurant. She uses valet parking. She issues credential C3 to the valet, allowing him to drive the car within 100 meters of the restaurant, for the next 2 hours while she is at the restaurant. Alice chooses to constrain C3 so the valet cannot further delegate. The valet uses C3 to unlock and drive the car to the parking garage.

Revocation

While Alice eats, law enforcement officers go to Ur Wheelz Houston with a search warrant for the car. They have discovered that the previous driver of the car was a criminal. They ask Ur Wheelz to revoke C2, because they don’t want the car to be driven any more, in case evidence is accidentally destroyed.

At the end of dinner, Alice goes to the valet and asks for her car to be returned. The valet goes to the car and attempts to open the door using C3. The car tests the validity of the delegation chain of C3, and discovers that C2 has been revoked, making C3 invalid. The car refuses to open the door. Alice has to take Uber to get home. Law enforcement takes possession of the car.