The Conditional Access System (CAS) technology is applied in pay TV systems to help the service providers to control users' authorization. So service providers charge subscribing fee by scrambling the program with conditional access system as well as control the illegal receiving the charged program in digital television (DTV) broadcasting. In this paper, we proposed a based on cryptosystem secure communication between set-top box and smart card in DTV broadcasting. Our proposed protocol has following merits: security, dynamic session key, mutual authentication and users could freely chosen password. Moreover, the proposed scheme could prevent smart card clone and MacCormac Hack problems which are serious problems in DTV broadcasting.