11 Encryption – DVB-CSA scrambling and Simulcrypt
Conditional Access System (CAS) general information
A conditional access system generally consists of two main subsystems:
■ A scrambling subsystem that a) scrambles the signal to prevent non-subscribers from receiving it and b)
descrambles the signal at the subscribers’ receivers.
■ An access control subsystem that processes access control messages to determine whether descrambling is to be
performed.
A Chameleon used in this context contains a Control Word Generator (CWG) generating Control Words (CW) for
the scrambling (DVB-CSA). To enable de-scrambling at the receiver side, the CW is transmitted in encrypted format
as ECMs. The ECMs are created by the CAS, based on the CW, and an Access Criteria (AC) supplied by the CAS.
The access control system is handled by EMMs. EMMs are received from the CAS, and included in the outgoing
transport streams.
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