full-disk subversion standards released

Alexander Klimov alserkli at inbox.ru
Sun Feb 1 09:45:24 EST 2009


On Sat, 31 Jan 2009, Peter Gutmann wrote:
> Even with the best intentions in the world, the only thing you
> can really usefully do with a TPM is DRM.

If there were a direct link from TPM to display and speakers and
all the content rendering were done by TPM itself, then TPM
would be useful for DRM. An attempt to render content "securely"
on CPU is based on a theory that content owner can trust general
purpose OS after "secure boot". Experience shows that this
theory is wishful thinking.

Apparently, the only existing application of TPM is BitLocker:
it allows to boot OS from an encrypted disk without entering any
password. A careful analysis shows that TPM is a separate chip
that can be powered down without reseting the CPU and thus one
can load "non-trusted OS", reset TPM, starts "secure boot", and
get encryption keys. Even when (if) TPM will be the same chip as
CPU, I suspect a man-in-the-middle attack on CPU-to-RAM
communication will allow to take over the "trusted OS".

On the other hand, once we forget about all attestation and
secure boot applications, TPM is still a smartcard soldered to
your computer, so probably it can allow all the smartcard
use-cases (except, of course, the uses-case that require storing
the smartcard separately from the computer :-).

-- 
Regards,
ASK

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