This document is the specification for an AV/C CA subunit. The CA subunit is a stand-alone piece of functionality that is used to descramble selected scrambled services. The model describes a generic functional block and command set that is compatible with multiple conditional access and broadcast systems. The CA Subunit provides the core functionality that is required to descramble selected services. The CA Subunit supports commands that allow the user to select a service or group of services to be descrambled, assuming that they have entitlement, and to query a future service for entitlement.