Re: A _good_ and valid use for TPM

[Robert Millan <rmh@aybabtu.com>]

On Sat, Feb 21, 2009 at 06:29:01PM +0200, Alex Besogonov wrote:
> On Sat, Feb 21, 2009 at 3:46 PM, Robert Millan <rmh@aybabtu.com> wrote:
> >> Yes, I'm trying to do remote attestation.
> > You're confusing things.  I think you simply want to ensure data integrity, and
> > the TPM doesn't even do that: it simply puts the problem in hands of a third
> > party.
> No, I'm not confusing anything.
> 
> > "remote attestation" is only useful when you want to coerce others into
> > running your (generaly proprietary) software.  I hope this is not what you
> > want to do.
> It's exactly what I want to do (minus the 'coercing' part). I want to
> ensure that devices run only my unmodified software (which I consider
> secure) and only in this case provide decryption keys for sensitive
> data. Of course, it done not for DRM purposes, but rather to protect
> sensitive data from theft (real theft, not copyright infringement).

There's no fundamental difference between hardening a device and using that
as your root of trust and using someone else's hardened device and using
that as your root of trust.  The only differences are:

  - One more link in the trust chain (irrelevant).

  - Because it's _someone else's_ computer (the TPM), you're irrationally
    assuming that its security is flawless.

  - Because it's someone else's computer, this helps them get their foot in
    your door.  Next time you notice, each PC will be verified by one of
    these, and then you can kiss all your freedom goodbye.

> >> Well, I spoke phcoder on Jabber - there might be a way to do this.
> >> He's going to investigate it.
> > This is unnecessary.  Once GRUB supports crypto, it can simply load
> > itself from an encrypted filesystem on disk.  An image can be of
> > arbitrary size.
> Nope. Still no way to test system integrity.

I was repliing to the idea of implementing sha-1 checks in the MBR.  Please
don't bring it out of context.

-- 
Robert Millan

  The DRM opt-in fallacy: "Your data belongs to us. We will decide when (and
  how) you may access your data; but nobody's threatening your freedom: we
  still allow you to remove your data and not access it at all."