There are two DVB protocols used by CA systems: SimulCrypt and MultiCrypt . SimulCrypt uses multiple set-top boxes, each using a different CA system, to authorize the programs for display. The different ECMs and EMMs required by each CA system are transmitted simultaneously. Each set-top box recognizes and uses the appropriate ECM and EMM needed for authorization. The ATSC standard uses SimulCrypt. MultiCrypt allows multiple CA systems to be used with one set-top box by using a PC card with an embedded smart card for each CA system used. Each card is then plugged into a slot in the set-top box. Each card recognizes the ECM and EMM needed for authorization.