Mode of Operation
A DVB receiver may have one or two slots implementing the Common Interface (CI). The CI uses the conditional access module(PCMCIA) connector and conforms to the Common Scrambling Algorithm (CSA), the normative that specifies that such a receiver must be able to accept DES (Data Encryption Standard) keys in intervals of some milliseconds, and use them to decode private channels according to a specific algorithm.
Those algorithms are proprietary to individual suppliers. Each one uses their own algorithms and there is no defined standard for them.
As the full MPEG-2 transport data stream comes out of the demodulator, and error correction units, the DTV Receiver sends it through the card plugged into the Common Interface, before it is processed by the MPEG demultiplexer in the receiver. If several CI cards are present, the MPEG transport data stream will be passed sequentially through all these cards.
An embedded CAM may not physically exist, as it may be in CPU software. In such a case, only the ISO card reader normally in the CAM is fitted and not the PCMCIA type CI slots.
Even if the Common Interface has been created to resolve cryptography issues, it can have other functions using other types of modules such as Web Browser, iDTV (Interactive Television), and so forth.
In Europe, DVB-CI is obligatory in all iDTV terminals.
Read more about this topic: Common Interface
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