[linux-elitists] Monday 15 Dec: first all-Open Source System-on-Chip

Seth David Schoen schoen@loyalty.org
Fri Dec 12 15:36:17 PST 2003


Peter Clay writes:

> On Thu, 11 Dec 2003, Seth David Schoen wrote:
> 
> > Therefore, the _availability_ of a valid encryption or decryption key
> > inside the TPM -- to make an unseal operation work properly -- depends
> > on what software is really running.  You can have many different
> > operating environments installed on a single PC -- differing by a
> > little or a while -- and in principle they cannot unseal one another's
> > sealed data at all, because each one has its own family of PCR values
> > that results when it's booted.
> 
> My understanding of this is that it renders the core code (that subject to
> PCR hashing) unpatchable, because if you ever change it you lose all your
> secured data.

That's correct, absent other data migration or recovery plans
supported by software.

> > The trusted computing applets are not supposed to have direct access
> > to any hardware
> 
> I find that surprising, as it renders them kind of useless for
> "protecting" audio. Do you know how this relates to the "Secure Audio
> Path" idea which was big last year?

I was told that it doesn't relate directly.  But you could imagine
having devices as part of Secure Audio Path that have certificates
that can be verified by software running under NGSCB.  They can
encrypt their audio output so that it can only be read by those
devices, although there is no way to prove that the device itself is
on a local platform as oppose to a remote platform.  So one relevant
attack might be creating a program that streams audio output from a
DRM client to a sound card on a remote system instead of a sound card
on a local system.  You apparently still get only one audio output
stream per client -- you would just get to decide which computer it
plays on.

> The "trusted worm" idea appeals to me; I've been kicking various versions
> of it around on mailing lists for a while now. Until I see a NGSCB machine
> I don't know exactly how it will work. Even if you can't create your own
> secure area, it should be possible to exploit someone else's, e.g. by
> buffer overrunning Windows Media Player. That would let you use its Super
> Sekrit Music Vault (or whatever) to store stuff where the user can't get
> at it.

That sounds like an interesting area for more research.

> The proposed Office document encryption and revocation features sound like
> fun. It could be the great extortion opportunity of the future - "We've
> taken all your document master keys. Send us $1000 if you ever want to see
> them again."

Did Microsoft say anywhere that it was going to include document
revocation in Office?

-- 
Seth David Schoen <schoen@loyalty.org> | Very frankly, I am opposed to people
     http://www.loyalty.org/~schoen/   | being programmed by others.
     http://vitanuova.loyalty.org/     |     -- Fred Rogers (1928-2003),
                                       |        464 U.S. 417, 445 (1984)



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