Captain Jack
Retired human
- Joined
- Oct 21, 2006
- Messages
- 11,850
- Reaction score
- 8,035
- Points
- 113
- My Satellite Setup
- See signature
- My Location
- North Somerset
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
Here's the result. Top image is the encrypted transmission from HackRF and bottom is the decrypted one.
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...
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
Here's the result. Top image is the encrypted transmission from HackRF and bottom is the decrypted one.
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...