| ]]Encryption (Scrambling)[[
The television and radio programmes which can be watched by anyone with a basic receiver are known as Free-to-Air (FTA).
Many broadcasters charge a subscription for their programmes, and to prevent unauthorized viewing the signals are scrambled (encrypted). There are several digital encryption systems - for example Cryptoworks, Conax, Irdeto, Mediaguard, Viaccess, etc. In Europe the majority of the few remaining analogue encrypted channels are beamed towards Scandinavia. These services use the MAC TV standard, and the scrambling system is Eurocrypt.
To unlock a channel the viewer needs a Receiver with a Conditional Access Module (CAM) that matches the encryption system being used. On payment of a fee the programme provider will supply the viewer with a viewing card containing special codes (called keys) to unlock only the subscribed channels. Copyright and other legislation normally does not allow the purchase and viewing of programmes in one country which are intended for another country (for example: it is not permitted for viewers in Spain to watch encrypted programmes 'aimed' at the UK by SkyTV).
Some Receivers are dedicated to one television network and one encryption system (for instance in the UK, SkyTV can only be picked-up on a receiver with an embedded (built-in) Videoguard CAM). In this case the subscriber's viewing card is linked electronically to one specific receiver.
Many Receivers are available with a common interface (CI). This is a single or double 'slot' into which one or more CAM's can be inserted. Once the CAM is in the receiver the necessary viewing card is inserted into the CAM.
The CAM has been designed to have the same physical format as a PCMCIA Card (which are extensively used in lap-top computers (Modems, etc)).
For the satellite enthusiast a wide range of experimental CAM's are available (Magic Module, Reality, Dragon, Matrix, etc). Many operate on several of the encryption systems.
There are a few Receivers on the market which have an embedded programmable CAM (so-called UCAS - Universal Conditional Access System). These Receivers usually have at least one additional slot for another CAM.
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