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

Christoph Schulz kristov at arcor.de
Wed Nov 2 08:26:10 CET 2005


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
cannot be used in such a case?

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?

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?

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!)

The information about my card printed by the driver is:

saa7146: register extension 'dvb'.
PCI: Enabling device 0000:00:14.0 (0044 -> 0046)
PCI: Found IRQ 9 for device 0000:00:14.0
PCI: Sharing IRQ 9 with 0000:00:07.2
saa7146: found saa7146 @ mem c88fac00 (revision 1, irq 9) (0x13c2,0x000a).
DVB: registering new adapter (Technotrend/Hauppauge WinTV Nexus-CA rev1.X).
saa7115 2-0021: saa7115 found @ 0x42 (Technotrend/Hauppauge WinTV
Nexus-CA rev1.X)
adapter has MAC addr = 00:d0:5c:04:48:47
dvb-ttpci: gpioirq unknown type=0 len=0
dvb-ttpci: info @ card 0: firm f0240009, rtsl b0250018, vid 71010068,
app 8000261d
dvb-ttpci: firmware @ card 0 supports CI link layer interface
dvb-ttpci: adac type set to 0 @ card 0
saa7146_vv: saa7146 (0): registered device video1 [v4l2]
DVB: registering frontend 0 (ST STV0297 DVB-C)...
dvb-ttpci: found av7110-0.


It would be very helpful if anyone could answer some of my questions or
put me in the right direction to search for further information. Also,
don't hesitate to ask if you need any further information I missed to
provide.

Regards,
  Christoph




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