On Feb 2, 2009, at 2:29 AM, Peter Gutmann wrote:
Mark Ryan presented a plausible use case that is not DRM:
http://www.cs.bham.ac.uk/~mdr/research/projects/08-tpmFunc/.
This use is like the joke about the dancing bear, the amazing thing
isn't the
quality of the "dancing" but the fact that the bear can "dance" at
all :-).
It's an impressive piece of lateral thinking....
I don't see that. The problem being solved is exactly a DRM problem:
A gives B some data but wants to retain control the circumstances in
which B can use that data. The algorithm proposed implements three
fundamental controls: (a) B can only access the data through a
particular program that A trusts; (b) B can "return" the data, along
with a proof that he never actually accessed it; (c) A can then revoke
B's access to the data (although the algorithm bundles this with
(b)). (a) and (c) are exactly the kind of thing DRM implementations
do all the time - and exactly the kind of thing that's been widely
discussed for TPM. (b) is novel.
DRM has to do with retaining access to data that has been provided to
an untrusted party. The entertainment industry considers its
customers untrusted, so TPM in its primary use cases is about
controlling what those customers - i.e., all consumers of computers! -
can do. In Ryan's use case, the untrusted parties are the government
security services. One can construct other untrusted parties as
well. In a cloud-computing world, wouldn't it be nice to know that
your data, all though it's "out there", being operated on by all kinds
of programs "out there", is still under your control? The problem
isn't with "DRM" in the large sense - it's that once you enable "DRM"
in the large sense, "DRM" in the small sense (as the entertainment
industry already sees it, and as many others will once the capability
is there) seems to be unavoidable. It's a matter of tradeoffs.
(Notice that the same people who say this tradeoff isn't worth it will
also say that the tradeoffs of broadly available crypto - yes, it
protects privacy, but that includes the privacy of criminals. I don't
think there's any broad principle that is being applied here - it's a
case by case analysis of the good and bad effects of particular
technologies. The DRM debate in particular is inherently tainted by
the actions and attitudes of the entertainment industry.)
-- Jerry
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