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Comment by billyhoffman | Hacker News Reader

The raw memory itself isn't safe either.

Ed Felton did some great work (2008) where he physically removed the sticks of DRAM from one computer, stuck them in another, and read their contents. But doesn't DRAM lose it's content without continuous power? Not if you turn a can of compressed air upside down and spray the chips first, cooling them to -50C! He used this to recover encryption keys and defeat whole disk encryption.

Pretty crazy stuff: https://citp.princeton.edu/research/memory/

update: link to images/videos: https://citp.princeton.edu/research/memory/media/

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For Linux there is TRESOR (http://www1.informatik.uni-erlangen.de/tresor). It uses CPU registers, which can prevent this sort of attack. However, you're limited to one encrypted drive with this method.

Modern CPUs have a lot of cache these days. Couldn't the keys be store there are well (assuming the threat is just the removal and reading of RAM)?

Hi. L3 caches are indeed huge these days. For example, the latest Mac Pros are shipping with 30MB L3 caches.

You can do a lot with that space. My company PrivateCore runs an entire Linux/KVM stack within the L3 cache, then fully encrypts main memory. Someone physically acquiring memory would only obtain plaintext.

Note that a software compromise could still read memory. That's one reason why it's necessary to fully attest a system before provisioning it with any keys or passwords.

Here's a CanSecWest talk with more details: http://cansecwest.com/slides/2013/PrivateCore%20CSW%202013.p...

You mean cypher text. Plain text is clear text is unencrypted.

Very cool! How small of a cache can you work in?

Thanks!

The caches are designed to be transparent, so you can't store data in them separately. Not to mention that your program could be interrupted at any point, so the OS would have to backup this data into ram (like it does registers).

TRESOR only helps against passive attacks since since the code is still exposed in memory. Active attacks that modify memory can easily circumvent it.

Not sure what you mean. TRESOR prevents cold boot attacks. If your Linux OS is compromised, TRESOR wouldn't help you anyway. But that's not the point of it, either.

Yes, TRESOR can help against cold boot attacks, which are passive and read-only.

Several physical attack vectors can modify the contents of memory, thus compromise the software stack and divulge keys kept in registers or cache.

Our approach at PrivateCore is to fully encrypt main memory with an authenticated cipher mode and keep the software stack pinned in cache. An attacker able to physically modify memory can only conduct a DoS attack by inserting junk data.

Doesn't work on DDR3 ram. Cold boot attacks are extinct. There's also stuff like this you can combine with encrypted swap http://www.onarlioglu.com/privexec/

So does this mean that the non-upgradeable computers with soldered RAM (i.e., MacBook Air) are more secure?

It means that they're resistant to that attack, sure (which is distinct from being "more secure" as if there were some continuum). The Air is also resistant to the firewire DMA attack, in that it doesn't have firewire

It should be resistant to the firewire DMA attack even if it had firewire. Modern processors protect against this. AMD calls their mechanism the device exclusion vector, I forget what Intel calls theirs.

IO virtualization (IOMMU) prevents this. Intel calls it VT-d.

Wouldn't the inclusion of Thunderbolt (similar concept to Firewire) make that some sort of attach still possible?

Thunderbolt doesn't provide raw access to DMA (and thus the ability to directly access any process's memory) the way Firewire did.

It seems thunderbolt in fact DOES provide raw DMA: http://www.breaknenter.org/projects/inception/

But at least on Macs, the attack is somewhat mitigated by the OS shutting off thunderbolt/firewire DMA if the screen is locked.

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