[linux-dvb] AV7110-based dvb-ttpci DVB card: Descramble an inadvertently scrambled recording?

Ralph Metzler rjkm at metzlerbros.de
Wed Nov 2 11:00:33 CET 2005

Christoph Schulz writes:
 > Hello,
 > please forgive me if this is the wrong mailing list to ask this question.
 > The problem: I made a TS recording with a Technotrend DVB-C card
 > (dvb-ttpci driver, AV7110 based) from a scrambled channel.
 > Unfortunately, the CAM was not properly initialized, so the recording
 > wasn't decrypted but saved scrambled on the disk. Now my question(s):
 > 1) Is it technically possible to replay the recorded TS stream through
 > the DVB card, using the CAM to decrypt it? I read somewhere that you can


 > feed an MPEG2 stream through the dvr device into the driver, but that
 > then the software decoder is used. Does this mean that the hardware CAM

No, but it is not passed through the CI interface.

 > cannot be used in such a case?

Yes, it cannot.

 > 2) Does the scrambled MPEG2 transport stream contain enough information
 > to allow a later descrambling to be performed successfully? I read
 > somewhere that a similar card does not record all the ECM/EMM
 > information needed for later decrypting. Is this true for my card?

You could record it with your card but you probably did not.

 > 3) If the stream does contain the required information but the hardware
 > is not capable of descrambling a recording, is it possible to use a
 > software-based approach? I mean, is it possible to use/write a program
 > that communicates with the hardware CAM directly to decrypt the
 > recording stream?

Not without extra hardware. E.g. a normal PCMCIA interface would not
work and I am not aware of any that would do that.

 > 4) If one cannot use the hardware CAM, is it possible to use a
 > software-emulated CAM? (I read about it in some Windows forums.) Does an
 > emulated CAM exist for Linux? And if so, does anyone know if it is legal
 > to use it with your own recordings provided you have a legal
 > subscription? (Of course I have a subscription!)

IANAL and I am certain there is some obscure interpretation of some 
law which will say either way ...


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