Conditional Access(CA) is a procedure for access authorization to encrypted television, video and radio broadcasts. A combination of scrambling and encryption of the message protects it from unauthorized reception. The scrambled video and audio signals can only be displayed with the correct key.
Scrambling can be basic encryption, which ensures that only those recipients who have paid for the cable connection can access it. However, encryption can also go beyond basic encryption and include additional program encryption and encryption for young people. These tasks are performed by the provider using the Subscriber Management System( SMS) and the Subscriber Authorization System( SAS).
In terms of reception, decryption takes place in the set-top box with a CA module and the Common Interface( CI); in the case of Digital Video Broadcast( DVB), it is the DVB Common Interface( DVB-CI). The process is also suitable for Internet broadcast services via satellite such as DVB-S and can also be used in other terminal devices such as multimedia PCs, PDAs or cell phones.