Television encryption
The prevention of piracy on cable and satellite networks has been one of the main factors in the development of Pay TV encryption systems.
The early Pay TV systems for cable television were based on a number of simple measures.
As the number of television channels on these cable networks grew, the filter-based approach became increasingly impractical.
Other techniques, such as adding an interfering signal to the video or audio, began to be used as the simple filter solutions were easily bypassed.
As the technology evolved, addressable set-top boxes became common, and more complex scrambling techniques such as digital encryption of the audio or video cut and rotate (where a line of video is cut at a particular point and the two parts are then reordered around this point) were applied to signals.
Unfortunately for that company, an electronics magazine, "Radio Plans", published a design for a pirate decoder within a month of the channel launching.
The VideoCipher II system proved somewhat more difficult to hack, but it eventually fell prey to the pirates.
[citation needed] Analog and digital pay television have several conditional access systems that are used for pay-per-view (PPV) and other subscriber related services.
In some of these systems, the necessary sync signal was on a separate subcarrier though sometimes the sync polarity is simply inverted, in which case, if used in conjunction with PAL, a SECAM L TV with a cable tuner can be used to partially descramble the signal though only in black and white and with inverted luminance and thus a multi standard TV which supports PAL L is preferred to decode the color as well.
Other commercial digital encryption systems are, Nagravision (by Kudelski), Viaccess (by France Telecom), and Wegener.
In the US, both DirecTV and Dish Network direct-broadcast satellite systems use digital encryption standards for controlling access to programming.
[citation needed] In Canada, both Bell Satellite TV and Shaw Direct DBS systems use digital encryption standards.
Oak Orion was originally used for analog satellite television pay channel access in Canada.
Leitch Viewguard is an analog encryption standard used primarily by broadcast TV networks in North America.
RITC Discret 11 is a system based on horizontal video line delay and audio scrambling.
Used by German/Swiss channel Teleclub in the early 1990s, this system employed various methods such as video inversion, modification of synchronisation signals, and a pseudo line delay effect.
An older Nagravision system for scrambling analogue satellite and terrestrial television programs was used in the 1990s, for example by the German pay-TV broadcaster Premiere.
In this line-shuffling system, 32 lines of the PAL TV signal are temporarily stored in both the encoder and decoder and read out in permuted order under the control of a pseudorandom number generator.
The system also permitted the audio signal to be scrambled by inverting its spectrum at 12.8 kHz using a frequency mixer.
