Seth on TCPA at Defcon/Usenix

[Joseph Ashwood]

----- Original Message -----
From: "AARG! Anonymous" <remailer at aarg.net>
[brief description of Document Revocation List]

>Seth's scheme doesn't rely on TCPA/Palladium.

Actually it does, in order to make it valuable. Without a hardware assist,
the attack works like this:
Hack your software (which is in many ways almost trivial) to reveal it's
private key.
Watch the protocol.
Decrypt protocol
Grab decryption key
use decryption key
problem solved

With hardware assist, trusted software, and a trusted execution environment
it (doesn't) work like this:
Hack you software.
DOH!!!!! the software won't run
revert back to the stored software.
Hack the hardware (extremely difficult).
Virtualize the hardware at a second layer, using the grabbed private key
Hack the software
Watch the protocol.
Decrypt protocol
Grab decryption key
use decryption key
Once the file is released the server revokes all trust in your client,
effectively removing all files from your computer that you have not
decrypted yet
problem solved? only for valuable files

Of course if you could find some way to disguise which source was hacked,
things change.

Now about the claim that MS Word would not have this "feature." It almost
certainly would. The reason being that business customers are of particular
interest to MS, since they supply a large portion of the money for Word (and
everything else). Businesses would want to be able to configure their
network in such a way that critical business information couldn't be leaked
to the outside world. Of course this removes the advertising path of
conveniently leaking carefully constructed documents to the world, but for
many companies that is a trivial loss.
                Joe


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