Lair Of The Multimedia Guru


Decrypting (old analog) PayTv

A really long time ago, 1997 or maybe it was even a little earlier i wrote a program to decrypt the at that time used analog pay tv systems videocrypt and nagravision sadly i was too afraid of legal issues at that time so i never released either source or binary, well both systems are AFAIK dead nowadays, the old code hasnt been touched since 2000, doesnt compile with any compiler i have, so i thought its the perfect time for finally releasing that trash

When was the first working version born?

well i dont know, the oldest file i could find was a 2do list from 1997 which contains notes about improving videcrypt and nagravision decoding so these must have been working already …

Does it contain any cryptografically new knowlegde about the systems

no, before the nagra PRNG was reverse engeneered i belived that the PRNGs both systems used would be very secure and there would be no point in “looking” at their output, afterwards besides feeling silly as even a blind man would have noticed how the nagra PRNG works (its just permutating 256 5bit values in trivial 32768 ways, 127 only if we ignore new[x]= old[x+C])
i tried to look at the videocrypt PRNG output but failed to find anything, 2 cutpoint sequences where either different and their difference random or there where exactly equal, which happened either commonly (repeating after an hour or so) or never, depending upon when you recorded them, i also failed to find any other relations in the sequences …

Is this clean ANSI C code?

its ultra messy DJGPP-GCC-DOS-C code, i started to clean it but gave up, a patch with my unfinished cleanup work is included for the insane. with the patch a few files compile under current gcc-linux

what else does it do? could it make coffee?

Theres some teletext decoding code, some half working sync suppression decoder (with unmodified hardware) and probably a few other things i dont remember, after all it doesnt compile and i dont have my matrox meteor card here (which was the only card it supported, as that was what i had)

did you port it to java?

yes, i ported part of it to java a really long time ago, why i did that iam not sure anymore, was i seriously beliving the sun propaganda that java was a useable general propose programming language?i guess my excuse is that my previous java code at that time where just tiny applets & applications where the java-effect isnt so noticeable
the java version was even with hand coded mmx over jni about 3 times slower, there where ~1sec garbage collector pauses every 30secs or so and after 15min the computer needed a hard reset (yeah that was even without any mmx/jni)

download this crap\h\h\h\hmasterpiece



GPL but what do you want to do with it?!

Filed under: Cryptanalysis — Michael @ 14:37


  1. AFAIK nagra is still used on a french secam channel named canal +.

    I you are still interested in the subject, there are some code for Linux (taztv, xawdecode) and windows (ktv) on

    Comment by anonyme — 2006-04-08 @ 18:16

  2. Sky TV in New Zealand still uses videocrypt on its uhf stream.
    I would be keen to give your software a go to see if it can decode it.
    What does it require to run?



    Comment by Sam — 2006-12-15 @ 23:07

  3. from the HW side a matrox meteor card (it will not work with BT* cards but porting it should be easy, actually it should work better with the BT8x8 cards as their combfilter can be disabled …) and some VESA2 VGA card (=any grafic card)

    from the SW side well i used it under windows 95 or so, plain dos might have worked too (latest and greatest windows xp,nt,2000 will likely not work as 2010 accesses the hardware pretty directly)

    from the compiler side djgpp-gcc and nasm was used

    all IIRC, this is from memory and probably not 100% correct as its long ago

    PS: if you do get it working again iam certainly interrested to hear about it, also iam certainly interrested in any patches/improvements/fixes anyone makes …
    PS2: recording some of the encrypted videocrypt/nagra stuff into a lossless format (huffyuv/ffv1) might be funny so geeks could play with decrypting it even if these old analog encryptions disapear entirely …

    Comment by Michael — 2006-12-16 @ 01:17

  4. Hi, I am looking for a novice guide to decrypting Nagravision analouge.
    CANAL+ still transmit on 5W, but won’t sell the cards anymore making it impossible to buy one so one has no choice other than to resort to other methods. (OK, one could go digital but this involves buying a new receiver and loosing the other analouge SECAM channels :(

    Comment by none — 2008-01-04 @ 15:54

  5. Hi. Could anybody send me a program to decrypt Videoguard channels on Amos 1/2 with my Season Interface?
    I’m using Win XP, Humax Va-Fox, Season Interface from WedzBoyZ
    Thanks a lot
    Best regards

    Comment by Alex — 2008-01-23 @ 00:27

  6. In years past , you would have had only a few basic alternatives when choosing Television cable, Satellite or old fashioned over the air . But a fourth choice is worth thinking about . It’s know as , IPTV . So I advise you get rid of that bt8x8 tv software and break free from monthly bills as soon as possible .

    Comment by James — 2012-01-13 @ 17:27

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