Re: A _good_ and valid use for TPM

[Jan Alsenz <janalsenz@student.ethz.ch>]

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Robert Millan wrote:
> On Sat, Feb 21, 2009 at 03:20:39PM +0100, Jan Alsenz wrote:
>>> "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.
>> Yes, this is exactly what he tries do to: convince his keyserver, that the
>> requesting server runs, what it's supposed to.
>>
>> Which is exactly remote attestation, just in this case he controls both sides,
>> which I think makes it an interesting use of the technology.
> 
> That would be like trying to rob yourself by threatening yourself with a gun,
> instead of simply drawing money from your wallet.

Sorry, I don't get that analogy...

> If you just want to ensure noone is tampering your box, simply make your box
> tamper-proof.  You don't need a protocol to allow third parties to check
> anything.

Ok, but if you have such a protocol, only use it for yourself and do trust the
manufacturer, you only have to secure one of your boxes instead of them all,
which is usually much easier.

>>> 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.
>> Ok, but where does it get the key from?
> 
> The public key (or just a hash) can be embedded in GRUB itself.  In the
> instance of GRUB that goes to the flash chip, that is.
> 
>> And how can wherever the key comes from be sure that it's talking to GRUB?
> 
> Because you put it there, and made sure noone can overwrite it afterwards.

Making sure, that noone can override it, can be awfully difficult, especially
under a physical attacker. A hardware that is at least a bit designed to
withstand such an attack can help a lot.

Greets,

Jan


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