Fedora reexamines "trusted boot"

Posted Jul 1, 2011 14:16 UTC (Fri) by nix (subscriber, #2304)
In reply to: Fedora reexamines "trusted boot" by Cyberax
Parent article: Fedora reexamines "trusted boot"

Right. So the former mode is fine -- but as far as I can see doesn't really need more hardware support than a bit of NVRAM. The latter mode, which actually requires crypto and so on, is as far as I can see evil, because it locks keys up in opaque and failure-prone hardware, thus effectively doing a delayed deletion on any data secured by it and a delayed DoS on any access granted by it (because hardware always fails in the end).

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Fedora reexamines "trusted boot"

Posted Jul 1, 2011 15:18 UTC (Fri) by Cyberax (✭ supporter ✭, #52523) [Link]

Uhm. Private key mode is not (generally) used to encrypt data, so no worries about data loss.

It's used to make your machine 'uncloneable' and prove it to a remote party. It can be used for DRM (so you can view content only from uncloneable authorized devices) or to make sure that if your server is stolen you can make it unusable for the thief. We actually used TPM for this exact purpose - to make servers with medical data secure against physical theft.

Fedora reexamines "trusted boot"

Posted Jul 2, 2011 10:52 UTC (Sat) by Cyberax (✭ supporter ✭, #52523) [Link]

BTW, 'a bit of NVRAM' won't work to store encryption keys. Because an attacker can just boot a LiveCD/LiveUSB and read all your keys from NVRAM.

That's where the measurement part of TPM comes handy - TPM won't release keys unless your system is secure.

Fedora reexamines "trusted boot"

Posted Jul 7, 2011 17:34 UTC (Thu) by farnz (subscriber, #17727) [Link] (1 responses)

I've used the unknown private key mode - the point is to provide me with a way to confirm, beyond all doubt, that the accesses I'm seeing are coming from my trusted hardware, running my trusted OS. Change the OS, or change the hardware, and you need reauthorising with a new key to get on the network; similarly, you can use the hidden private key for encryption of your disk's AES key, which is also stored offline somewhere physically secure. You can thus get the key out again when the TPM fails (and recover your data), it's just hassle typing it in from your laminated printouts. In the meantime, the TPM lets you forget that there is such a key - the hardware knows what it is and ensures you always run a known-good OS.

The evil in TPM is nothing to do with the technical capabilities of the chip - they're fairly innocuous, if tricky to use well; the danger is when the TPM chip is used to store a private key that the user did not ask it to generate; in this situation, the holder of the public key has a path all the way to the machine that bypasses the user's wishes. If the user generates the key and hands the "public" section to the third party, all is well - nothing stops the user lying to the third party and giving them a public key not generated by a TPM.

Fedora reexamines "trusted boot"

Posted Jul 8, 2011 12:44 UTC (Fri) by nix (subscriber, #2304) [Link]

Ah, right. That makes things much clearer.