🚀 go-pugleaf

In article <C0B6Fx.74D@cantua.canterbury.ac.nz> geoffrey@cosc.canterbury.ac.nz (Geoff Thomas) writes:
>
>Anybody know how the VIDEOCRYPT encryption system works?
>It is manufacted by in the UK by Fergusson Ltd. The
>decoder has a smart card which needs to be inserted into
>it for it to decode the video signals (audio is unscrambled).
>

Videocrypt uses a method of scrambling known as "cut and rotate". All the sync
pulses are left intact. Each line of video has what is known as a cut point.
The line of video is transmitted with the video portion from the cut point to
the normal end of line first, followed by the normal start of line to cut
point next. The cut point varies from line to line and may be in 1 of 256
possible locations (I may be confusing a similar system here). When viewed
all that is seen is an unintelligle mess. The audio is not scrambled and
sits on a carrier of 6.5MHz (and possibly 7.02/7.20MHz for stereo 
sub-carriers).

The receiver digitises each line of video and stores the result in a memory 
chip. A special secure processor tells another chip where the cut point is, 
and the data is extracted from the memory in a different order from which it 
went in. The data is then passed through a DAC to restore the original video 
line.

Access is controlled by a "smart card" inserted in a slot in front of the
receiver. The smart card is believed to be based around a microprocessor
itself. Some decoders can suffer from black streaks across the picture
under some conditions. This encryption is used by BSkyB and other UK program
material providers on the Astra satellite. A number of UK satellite
manufacturers build videocrypt decoders into their receivers. Both Pace
and Ferguson manufacture stand alone decoders - although the Ferguson is
now a little old in the teeth.

--Gary
+---------------------------( Gary Morton )-----------------------------+
|Disclaimer: The opinions above are my own personal views etc.          |
|Inmos Ltd, 1000 Aztec West, Bristol, UK         Email : gary@inmos.com |
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