[mythtv-users] CableCard Chain.

Raymond Wagner raymond at wagnerrp.com
Wed Jul 25 02:37:04 UTC 2012


On 7/24/2012 21:53, Chuck Peters wrote:
> On Tue, Jul 24, 2012 at 9:05 PM, Devin Heitmueller
> <dheitmueller at kernellabs.com <mailto:dheitmueller at kernellabs.com>> wrote:
>
>     On Tue, Jul 24, 2012 at 8:37 PM, Chuck Peters <cp at ccil.org
>     <mailto: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.

Windows is a closed source platform.  You cannot simply modify the code, 
and add in a new interface to access the unencrypted video.  Even if it 
were open source, you would only be able to access the content on the 
original binary distribution, as that would be the only version known to 
maintain the DRM.  Additionally, Windows Vista and 7 implement a 
"protected video path" to prevent users from writing additional software 
that attempts to intercept the data at any point on the system.

> after running mythtv since 1996

Would that be 2006?

> I haven't found anything that will allow Windows XP to record or
> play protected-copyonce streams.

Windows XP does not have the protected path incorporated into Vista, 
which is why Microsoft has never certified it with CableLabs, and also 
why there are difficulties playing some Bluray content.

> 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.

Yes and no.  By being given the only keys to the system, CableLabs has 
afforded cable companies a near monopoly on what hardware can connect 
directly to cable networks.  They have very strict requirements, and 
very high certification fees, that has resulted in nearly no third party 
hardware available for purchase in the more than half decade since the 
module CableCard access system became a federal requirement.

However, the core problem is DRM.  DRM demands a closed source 
environment, or at least one with signed, uneditable binaries. 
Conditional access itself is not a problem, as it is only a closed 
system up until the point that it is unencrypted and handed off to the 
3rd party hardware.  With DRM, the entire chain of software and hardware 
that touches the unencrypted content must be free of user control, as 
its only purpose is to restrict user access.  You don't actually own 
anything you may have purchased that is protected by DRM, you are merely 
allowed to access it in an approved manner, for now.

Complain about CableCard all you wish, but the simple fact is that the 
ideals of DRM and the open source community are categorically opposed. 
If CableCard gets replaced by something else, that something else will 
still be protected by DRM, and since MythTV cannot maintain that DRM and 
still be capable of user modification, MythTV will not be allowed to 
access any content through it.  You're right back in the same situation 
we have now, where DRM-free content using a CableCard tuner as a 
conditional access system works great, but for any DRM-protected 
content, you're hosed.


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