[linux-elitists] defanging TCPA?

Martin Pool mbp@sourcefrog.net
Fri Feb 7 17:43:58 PST 2003

On  7 Feb 2003, Seth David Schoen <schoen@loyalty.org> wrote:

> I don't think Felten's observation eliminates the possibility of
> making devices which do _both_.
> See "One way to think about trusted computing" at
> http://vitanuova.loyalty.org/2002-11-06.html

That's a really good article, but I don't think it rebuts Felten's

To continue with your gedankendesign, it seems like it would be
necessary for the media player to have its own sound and video output:
if they were sent back to the computer they might be recorded.  And
the designers would be very leery of any firmware upgrade mechanism
for the player, in case it was used to subvert it.  The situation is
similar to a computer-controlled VCR or laserdisc player.

This kind of thing, perhaps literally with a firewire attachment,
seems to me to be far more technically viable than DRM done in a
general-purpose PC.  I don't know if the content available this way
would be sufficiently attractive to encourage people to buy the extra

I think Felten's statement still holds because you have a system of
two communicating devices, rather than a single device.  If you try to
remove the firewalls between them then you get into the difficult
middle ground.   

Felten's rule points out why this is such a good design: we leave a
gap in the middle where the difficult part is.

>  you can build a Turing machine and put it in a box with some other
>  kind of machine, and it's still a Turing machine.

Yes, but if the other machine is not under the control of the first
part, then it is not really in any sense part of a Turing machine,
aside from a shallow physical one.


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