Hi everyone, I found the great question on booting encrypted drives, and since I’m somewhat paranoid I’d like to ask a follow-up:
When the key to decrypt the drive is input into the system, I’m assuming it stays in the RAM till the time the computer shuts downs. We know that one could, in theory, get a dump of the contents of the RAM in such a state, if done correctly. How would you deal with this problem? Is there some way to insert the USB, decrypt the drive, and then remove the USB and all traces of the key from the system?
Thanks!
Edit: link to the question I referenced: https://feddit.de/post/6735667
That’s not possible because of the way disk encryption works. When you unlock an encrypted drive, it does not actually decrypt it - that would take way too long and leave the disk unencrypted. Instead, the computer keeps the key in RAM and uses it to decrypt the accessed data blocks on the fly.
I wouldn’t attack via USB, that path has already been too well thought out. I’d go for an interface with some sort of way to get DMA, such as:
- PCIE slots including M.2 and external thunderbolt. Some systems might support hotplug and there will surely be some autoloading device drivers that can be abused for DMA (such as a PCIE firewire card?)
- Laptop docking connectors (I can’t find a public pinout for the one on my Thinkpad, but I assume it’ll have something vulnerable/trusted like PCIE)
- Firewire (if you’re lucky, way too old to be found now)
- If you have enough funding: possibly even ones no-one has thought about like displayport + GPU + driver stack. I believe there have been some ethernet interface vulnerabilities previously (or were those just crash/DOS bugs?)
Thank you, I’ll need to think more about possible attack vectors
I’m assuming it stays in the RAM till the time the computer shuts downs
Correct.
We know that one could, in theory, get a dump of the contents of the RAM in such a state, if done correctly.
An example of such an attack would a “cold boot attack”.
Is there some way to insert the USB, decrypt the drive, and then remove the USB and all traces of the key from the system?
It sort of depends on how the underlying hardware is designed. You can create a system in which the RAM’s contents are encrypted by the hardware, but at some point the data must be decrypted for use. For example, one could theoretically sniff the data-lines between the RAM, and the CPU. This is all of course ignoring the fact that the hardware, itself, could be compromised i.e. Intel M.E., backdoors/vulnerabilities in the BIOS, etc. There’s lots that can be done to try to mitigate security vulnerabilites, but there is always a tradeoff between security, and convenience.
Maybe the best form of security is memorizing a private key, then manually doing the math with a pen and paper to decrypt some text, and transmit it with a carrier pigeon.
Thanks
Sharing this article as I think it ties in with this conversation well: https://www.zdnet.com/article/cryogenically-frozen-ram-bypasses-all-disk-encryption-methods/
I do want to say that for most people, this is likely NOT a concern, but I don’t know OPs threat model.
For those not clicking the link, “cryogenically frozen” actually means an upside down can of compressed air.
On the other hand, it’s also worth noting that newer RAM generations are less and less susceptible to this kind of attack. Not because of any countermeasures, they just lose the data without constant refreshing much quicker even when chilled / frozen, so the attack becomes impractical.
So from DDR4 up, you’re probably safe.
That was a perfect one sentence summary of the article!
Its amazing some of the things people come up with like gathering intel on what a computer is doing via power draw changes, monitoring an air-gapped computers electromagnetic fields, or in this case “cryogenically” freezing ram with compressed air.
OP is likely Raoul Silva, the antagonist from Skyfall (2012).
