[mythtv-users] CableCard Chain.

Chuck Peters cp at ccil.org
Wed Jul 25 01:53:09 UTC 2012

On Tue, Jul 24, 2012 at 9:05 PM, Devin Heitmueller <
dheitmueller at kernellabs.com> wrote:

> On Tue, Jul 24, 2012 at 8:37 PM, Chuck Peters <cp at ccil.org> wrote:
> > Tivo was, and probably still is, running Linux, so why is it technically
> > insurmountable for MythTV to get certified by CableLabs?
> The way most of these hardware designs work is the encryption is done
> in hardware and the operating system never has access to the
> unencrypted stream.  It comes in on the cable card, gets reencrypted
> in silicon using keys built into the chip, and the encrypted stream is
> stored on disk.  Then when playback is needed the encrypted stream is
> read off disk, fed into the on-chip decryption engine and the
> resulting stream is funneled out the video output.  The point is that
> the operating system can never actually see the unencrypted stream.

OK, except that it doesn't seem possible that this is just hardware based
because WMC (Windows Media Center and Windows 7) will record and play (on
the machine it was recorded on) video streams with the CCI flag set as
protected-copyonce.  In other words WMC is storing the recording encrypted
and can only be played by that machine, or a so called media extender.  And
it seems the only media extender currently being manufactured is Xbox 360.

I am trying to get a better understanding of why after running mythtv since
1996 and being forced by our local cable company to convert to digital,
they will force me to pay for channels I can't watch, and upgrading to
their so called "Digital Basic" they will allow me to watch 2 of 48
channels.  The lowest tier of this digital transition "Expanded Basic" has
26 channels set so we can't watch them.  We are getting screwed.

I haven't found anything that will allow Windows XP to record or
play protected-copyonce streams.  Was it the 1996 Telecommunications Act
that supposed to allow a proliferation of consumer devices, or some other
federal law...  And in 2011 the FCC added some rules regarding cable
companies and cable cards after threatening to make them get rid of cable
cards completely.  The only options for viewing protected-copyonce streams
are WMC, Tivo and cable company DVR's.  I think this cable card mess
started in the year 2000 or earlier and given that much time I don't see
how it can be a technical barrier, I think the cable companies via
CableLabs have gamed the system to create artificial barriers to prevent
this proliferation of consumer devices in large part because they rent and
sell more DVR's etc.


> The other approach is to allow the operating system access to the
> unencrypted stream, but use code signing to ensure that only the
> kernel that was provided by the vendor can access it (enforced in
> hardware or the boot loader).   In this case they can make the kernel
> source available, but without the code signing key you cannot run an
> unsigned kernel on the hardware platform.
> Most people don't realize it, but many of the settop boxes provided by
> the cable companies themselves run Linux.  Of course they are under no
> obligation to give you the GPL source, since the cable company is
> technically the owner of the hardware and you just lease it.
> Devin
> --
> Devin J. Heitmueller - Kernel Labs
> http://www.kernellabs.com
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