TRESOR Runs Encryption Securely Outside RAM

http://www1.informatik.uni-erlangen.de/tresor

by jgrahamc • 13 years ago

112 65 13 years ago

www1.informatik.uni-erlangen.de

ape4• 13 years ago

Now thats paranoid ;)

keyme• 13 years ago

Not really... I've seen a demonstration where a Truecrypt (or something similar) encrypted laptop is stolen. The machine is locked, but still powered on (very reasonable. You locked your machine and left your desk). This basically means that the AES key is in RAM.

The attacker/thief cools down the RAM with liquid nitrogen (to slow the discharge), inserts a bootable CD with a special tool to dump physical RAM on bootup, and quickly cycles the laptop battery (causing a cold boot).

Since the RAM is not zeroed on bootup, the "old" bits stay pretty much as they were (thanks to the cooling).

IIRC this allowed an attacker recovery of the key with a very high probability of success.

BWStearns2• 13 years ago

While everything you say is true, it would seem paranoid in many cases. I don't know how many neighborhood electronics fencers have liquid nitrogen laying around or the computer savvy to pull this kind of stuff.

If someone is after me who is using this methodology then I have seriously pissed off the wrong people. While you could argue that it's only paranoia if the object of preparation is not possible, I would say that you're at least one leg over the fence into paranoia-land if you're prepping against a cold-boot and don't have any nation state or corporate espionage level enemies.

vidarh• 13 years ago

Reminds me of old home computers, where the RAM was slow enough to discharge that you didn't need to bother to cool down anything: Flicking the power quickly enough on a C64 would often leave most of the memory intact.

tedunangst4• 13 years ago

If this is a concern, the solution is easy. Buy an SSD, turn computer off when you walk away, turn computer on when you come back.

The intersection of people vulnerable to cold boot attacks and people likely to be victims of cold boot attacks is hopefully the empty set.

tga_d2• 13 years ago

You don't actually even need to use liquid nitrogen. Much more common is chemical duster (hold the can upside-down and the boiling fluorocarbons will rapidly cool anything), or even nothing at all if you do it quickly. There are entire USB distributions dedicated to this sort of thing, and it has been done plenty of times outside of academic or professional settings. For example: http://revision3.com/hak5/coldbootattack

conductor2• 13 years ago

Elcomsoft Forensic Disk Decryptor [0] can find the decryption keys from the RAM dumps or hibernation files.

The RAM can be accessed using a DMA malware from the GPU/NIC/Intel ME or other devices which have a (micro-)processor and can use DMA [1, just submitted].

[0] http://www.elcomsoft.com/efdd.html

[1] https://news.ycombinator.com/item?id=6457069

tedunangst4• 13 years ago

Your backdoored DMA capable NIC can also just copy the plaintext out of RAM without futzing around with the key.

sweis4• 13 years ago

Here's a video of a malicious PCIe device extracting both plaintext and encrypted main memory: http://www.youtube.com/watch?v=chvJpEmXvDk

jws• 13 years ago

This keeps the AES keys in some x86 debug registers so they never appear in RAM and can't be accessed after a reboot.

zamalek• 13 years ago

Had to delete my comment :(. Thanks for clarifying that.

codex3• 13 years ago

Why not keep the keys in a TPM and pull them into "real" registers whenever the kernel context switches into a specially flagged AES decode thread, and zero them when context switching away?

EthanHeilman• 13 years ago

Here is an NSA slide where the NSA talks about exploiting Trusted Computing Platforms for intelligence[1].

The German government believes that the TPM is backdoored and a danger to security[2].

1: http://www.nytimes.com/interactive/2013/09/05/us/documents-r...

2: http://www.techweekeurope.co.uk/news/microsoft-seeks-calm-on...

jdjb• 13 years ago

Shouldn't this also be a really fast implementation since there isn't even the delay required to move items into/out of ram?

Also what happens if the scheduler moves the application out of running state?

DennisP• 13 years ago

Hm. Maybe Linux should fold this into the kernel.

barrkel2• 13 years ago

Debug registers are only accessible in Ring 0. I haven't looked at the implementation described, but I'd be surprised if it isn't a kernel module or something equivalent.

dmm• 13 years ago

Even if all of the AES state is kept in cache, the data to be encrypted would still have to be copied from ram or disk, right?

mindstab• 13 years ago

yeah but you can have an encrypted disk, encrypted ram, not so much.

mikeash2• 13 years ago

If you stream the data in from disk (e.g. read 1kB, encrypt 1kB, read 1kB, encrypt 1kB) then a cold boot attack only recovers one small chunk of data. Whereas if your keys are in RAM then a cold boot attack can recover the keys which can then be used to decrypt your entire hard drive.

barrkel2• 13 years ago

Debug register access is not necessarily as optimized as access to (e.g.) L1 cache.

Tomdarkness• 13 years ago

There is no application, it is a kernel patch.

rthomas6• 13 years ago

I'm not very knowledgeable about x86, but why do they have to use the debug registers if they're slower? I know in GCC you can mark registers as "do not touch" when you write assembly in C. Why not use more general purpose registers?

mikeash2• 13 years ago

Because the idea is to run it in kernel mode with arbitrary other software running on the computer. Asking other software to pretty please don't touch these specific registers isn't going to work, because there's no way to enforce that. The debug registers are perfect because they can only be accessed from kernel mode, not userland.

tptacek• 13 years ago

Registers you ask the compiler not to touch are still flushed to RAM on context switches, which defeats the purpose of this system.

shredfvz• 13 years ago

In the AUR: https://aur.archlinux.org/packages/linux-lts-tresor/

kephra• 13 years ago

/me sings, "Another one bites the Dust"

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dobbsbob3• 13 years ago

Didn't DDR3 ram basically make cold boot attacks obsolete? They don't hold any voltage when you power down long enough to even freeze the chips

MichaelGG• 13 years ago

Interesting, that sounds correct:

http://www1.cs.fau.de/filepool/projects/coldboot/fares_coldb...

Even with cooling they weren't able to recover. However, a warm reboot, would still work. Speculating, but some laptops might have a way to force a reboot like some machines have a reset button. That'd at least restart the system, although proper BIOS config should prevent that from being useful.

sigstoat• 13 years ago

hm, it looks to me like they just cover the sorts of temperatures you see in refrigerators.

any idea if work has been done on cryogenic temperatures?

jnt• 13 years ago

And to avoid keyloggers being installed when the machine is powered of, see STARK[1] from the same uni.

[1] http://www1.informatik.uni-erlangen.de/stark

sweis4• 13 years ago

TRESOR still leaves all the code and data exposed in memory. You can modify the code that's being executed in order to divulge the contents of the debug registers.

We're working on solving the malicious device and cold boot problem at PrivateCore. To do so, we're encrypting all of main memory and keeping plaintext state in the L3 cache.

Here's a resource page with links to the TRESOR paper and other resources: http://privatecore.com/resources-overview/physical-memory-at...

ris2• 13 years ago

Where's the source?

Or are you expecting us to trust your proprietary nonfree software without ever seeing it?

Good luck with that.

TRESOR Runs Encryption Securely Outside RAM

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