> I don't see anything in section-8 of the CDD that precludes such
> hardware.

But because it is not in there, users and developers cannot depend on it.

Any application that makes use of extra-CDD hardware is not deployable
on all Android devices, and would be a bad candidate for inclusion in
the Market.

A future CDD could possibly require a TPM or similar hardware, just as
it could require a higher minimum amount of RAM someday.

> The question is whether anyone is
> finding a compelling reason to go down this road.

So far, making good use of encryption + key storage/a TPM has proven
difficult on mobile devices, in large part due to the difficulty of
entering a good PIN or password at boot or (better) often. With Bit
Locker on a Windows 7 laptop, typing a good boot-up password is easy;
on a mobile it's very hard. And mobiles are generally always-on, so if
you lose the device in a cab, an attacker may well be able to figure
out a way to get the goods without ever needing the boot-up password.

Using a TPM to store keys without requiring a PIN/password is fine ---
Bit Locker even supports this mode --- but it has its problems too:

http://www.wired.com/gadgetlab/2009/07/iphone-encryption/

I'm not willing to go as far as Zdziarski and say "useless"; PIN-less
TPM encryption is actually a decent way to do remote wipe (as long as
you can send the wipe signal before the attacker wraps the phone in a
faraday bag). So it's a decent remote wipe feature, not a "useless"
encryption feature.

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