Analogue Nagravision (Syster) encoder

Captain Jack

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Splitting off from the MAC resurrection thread where there was a short of Videocrypt and Nagravision encryption, I thought it would be a good idea to actually decrypt the transmission!

Having tried various software Nagravision descramblers, I found that none at all were even thinking about decoding it. This is because the line shuffling that I was doing was completely random, whereas software decoders relied on a real known substitution table along with initial trial-and-error line comparison to find two randomly generated values at the encoder end.

Following the document here, along with some source codes available elsewhere, I managed to recreate a semi-working encoder, which follows the steps of the real one - using the substitution table. Ran the encrypted (in real time) stream through HackRF and captured it with a capture card through the likes of MoreTV and ... it worked! It's not 100% decryption (or rather encryption) as I am only encrypting a single frame at a time, whereas in a real encoder, the top 32 lines (or 64 counting odd and even fields) from the previous frame are shifted to the bottom of the existing frame. The decoder then rearranges that into a single frame through the use of buffers. As a result, the top part of the image is still encrypted but is still very watchable.

Getting close for Sats UK's own channel - subscription only £99.99 per month :D

Here's the result. Top image is the encrypted transmission from HackRF and bottom is the decrypted one.

Screenshot 2017-06-29 06.56.13.jpg

Would be great to actually have it working on a real decoder but without access to one, it will be tricky.

Hoping to potentially recreate it with Videocrypt though...
 
Captain Jack

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Been working some more on the 'encoder' (yes, bored...). Have now managed to get the encoded image to display near perfect (ignoring the colour). Still have one or two stray lines from somewhere but it would be very watchable :)

nagra.jpg
 
Analoguesat

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Excellent.

5 years after analogue satellite closed down we still have interesting threads popping up in the section! :D
 
2cvbloke

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Analogue never dies, it just becomes an amateur entertainment medium... :D
 
Analoguesat

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Analoguesat

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I was looking at the tp lists for 70W Star C2 om Lyngsat earlier - shes still carrying quite a few analogue C-band tps!
 
Captain Jack

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Yep, sadly pointing nowhere near the UK. Even though I can "see" it...
 
Captain Jack

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Been playing some more over the weekend to get the colour encoded correctly, or rather not touch it at all. The burst signals are not affected by Nagravision, only visible lines, which become out of phase with colour information and hence looking black and white. Restoring the lines to their original order restores colour.

Also had to get the 32 line buffer working correctly (the bit that's seen at the bottom of the encrypted video) else it was looking all out. Still a couple of stray lines but nothing major.

The decoder used is one of many software ones, which were used to decrypt real transmissions back in the day (hence the need to use Windows XP!):

 
Captain Jack

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There we go... almost perfect.

 
Dave5118

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Have you tried this on the C+ channel on the 5w multistream, or do you need info int was encrypted with? I believe cryptimage is supposed to try all the permutations to rearrange the picture, but I've never tried it, plus I doubt it would work quick enough on Live TV.

Only just realised where you got your avatar from now :D
 
Captain Jack

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Cryptimage still relies on a real known permutation table, which cuts down the guesswork significantly. The 5w stream is difficult to decode as only half of the screen is visible and it's too overcompressed. And they probably use an unknown permutation table (there were two known ones in existence).
 
Captain Jack

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Thanks to @fsphil, there's now a partially working encoder that works with real hardware decoders. Code hasn't been committed yet but I expect it will happen fairly soon.

 
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