11.1 Introduction

In general, a CA system is a system that provides access to users when specific requirements are met. These requirements can, for example, refer to identification, authentication, authorization, registration, payment, or a combination. One of the technical means to prevent unauthorized users to get access to services is encryption. In the context of pay-TV, a CA system ensures that only authorized users (i.e., users with a valid contract) can watch a particular programming package ^[1]. In technical terms, a television program is broadcast in encrypted form and can only be decrypted by means of a set-top box. The set-top box incorporates the necessary hardware, software, and interfaces to select, receive, and decrypt the programs.

Chapter 3 discusses the interests of the several parties involved in CA. This chapter details the technical aspects of CA, explaining the basic elements of a CA system encryption, key management, subscriber authorization, and subscriber management and discussing the DVB specifications for the common scrambling algorithm (CSA) at a functional level. The CSA was developed to encrypt programs in a uniform way. This uniform encryption algorithm forms the basis of three different models of CA. In the Multicrypt model, a common interface allows a multitude of different service providers to make use of the same set-top box, in which the CSA is implemented. Within the Simulcrypt model, the CSA allows the same transponder channel to be shared by different service providers. This allows the same program to be received by both service providers ...