The conditional access system in a single frequency network in a digital broadcasting system includes a main broadcasting system transmitting encoded broadcasting signals including a data stream and transmitter identification information (TII) through a main broadcasting network; a repeating system amplifying and transmitting encoded broadcasting signals of the main broadcasting network, or modulating and amplifying a stream input by the main broadcasting system through a cable, and repeating broadcasting signals of the main broadcasting system through a repeating network; a subscriber station decoding the encoded signals of the main broadcasting network included in the broadcasting signals received through the main broadcasting network or the repeating network, TII, and an encoding key according to a decoding method; and a decoding key provider receiving a decoding key from the main broadcasting or repeating system, authenticating a user, and transmitting the decoding key to a charged subscriber station through a mobile communication network.