DISCRET 11: Canal+ Encryption 1984
The circuit is based on a pirate decoder from french Radio Plans magazine published in 1984.
The encoding was made by delaying image lines according to an algorithm that repeats every 6 frames, resulting in an horizontal displacement of those lines in a pseudo-random way. Each line can be displayed ether normally, delayed one time or delayed two times. A better explanation is available (in French) on Wikipedia
(translated from French)
Discret11 is the name of a former analog video encryption system or conditional access , designed for pay television. It has been used by french TV channel Canal+ since it’s release on 4th November, 1984 until 1995.
Discret 11 was used by different pay television channel to protect their broadcast. This name also describes the decoder using this standard. In France, Canal + used it as its first encoding system before replacing it by the Syster decoder in 1995 (after the Discret11 hacking had been made to easy).
Discret 11 was an encryption system based on image lines. Lines on the screen were affected by a pseudo random delay of 0, 902 and1804 nanoseconds to the right, with the help of 2 delay lines.
The name Discret11 had been chosen cause the encryption system used 2^11 combinations, which makes 2048 possibles codes. In fact, there was only 2047 cause the “clear” (non-encrypted) mode was part of those combinations.
Each first monday of the month, the code used to decrypt was changed. At broadcast, the encoder delayed the lines of 0, 902 et 1804 nanoseconds, and upon reception, the decoder “canceled” those delays by making sure every lines had 1804 nanoseconds delay.
The decoding was now valid and the image was displayed “clear”. If a wrong code was entered, the delays weren’t canceled and lines were delayed again in superposition of the coding already broadcasted, resulting in a double-coding . In this case, only sound was decrypted.
Sound was only transposed and its frequency spectrum reversed around 12,8kHz. To activate sound decoding, the decoder had to detect the white and black level of line 310 and 622. The signal processing was entirely analog and monophonic. Using satellite television , which permitted stereophony, sound wasn’t encrypted, but the satellite receiver needed to be configured in a particular way to avoid re-encrypting the sound again while the video signal was decrypted.
NOTE : There was also a Discret12 system, which used 2^12 combination, so 4096 possible codes. Sound was not encrypted and it has been used in analog by Italian RAI TV channel in June/July 2002 with Hotbird 13° satellite and during the 2002 Football World Cup, to protect their broadcasting rights.
This image line encryption system has been abandoned since pirating it had been made to easy.
Here’s an exemple of the original encryption:
I had in mind to reproduce this effect, so I looked for official decoders schematics, and I finally found a schematic from Radio Plans magazine for an all analog decoder, perfect for using it with modified video circuits.
Now, still to find how to crypt instead of decrypting. The original decoder circuit used some logic circuitry to detect which line were delayed or not, and then delayed every line accordingly so they all have a 1804ns delay in the end.
In my circuit, each line is delayed (or not) according to the horizontal sync pulse or subdivisions of it (each image line, 2 lines, 4 lines, etc..), resulting in periodic and quite harmonious displacements, as opposed to the original coding which is periodic (because pseudo random) but also chaotic.
Some exemples without random:
I managed to get something similar to the original coding by using the hsync pulse with a Yusynth Random Gate , and using only half of the outputed gates.
Pictures of the random feature:
Here with a modified video enhancer before the Discret11:
First test on veroboard (pardon the mess):
More info soon.