The invention provides an improved conditional access system with efficient bandwidth usage on the interface between a receiver and a conditional access module. The conditional access system has a receiver, a selection module, a conditional access module and possibly a terminal. The conditional access module has a first memory for storing service identifiers of services and transmits one or more service identifiers to the selection module. The selection module receives an input signal from,the receiver and selects from the input signal those sub-signals as identified by the service identifiers and transmits the sub-signals to the conditional access module.