5 ms·

I asked about this just the other day because I use full-disk encryption, but rarely shut the machine down (just sleep with screen lock). The responder was fai

I asked about this just the other day because I use full-disk encryption, but rarely shut the machine down (just sleep with screen lock). The responder was fairly confident that this was not a concern, but Inception does not require an implausible level of expertise to use, yet it would render my encryption useless (assuming the driver is present). https://news.ycombinator.com/item?id=7113788 https://news.ycombinator.com/item?id=7113788 A couple years ago, I chased down and tackled a guy who snatched my laptop on the Blue Line in Chicago. The threat of laptop theft is real and I'd like to mitigate the damage that would result without compromising my ability to work.

MichaelGG 13y ago
On OSX, IIRC, FireWire DMA was disabled if full disk encryption is turned on. Windows similarly has some sort of security advisory or capability wrt FireWire. If other ports are exposed that offer DMA capabilities, then they need to be disabled. Don't load the drivers/epoxy the physical ports. I was not aware that a new connector would reopen such a massive vulnerability. (Docking ports may also have some issue, but since they're proprietary it wouldn't matter.) That said, I think my assessment is still accurate. If you're just worried about a theft, it seems very unlikely they'd run these kinds of tools before restarting. And even then, why bother? Why not just reformat the machine, if it's just a theft? If you have actual enemies "then keep your laptop physically secured and powered off. And don't use it after breaking chain of custody." The really shitty thing is that some new laptops (W540) apparently don't ship DisplayPort or other digital video, but just Thunderbolt.
c0nsumer 13y ago
What's even niftier is, say with Windows and BitLocker, the BitLocker key can be recovered from a memory dump pulled this way. Couple this with live patching of RAM to bypass the lock screen and you're just kinda sunk. And yes, me, a not particularly security-oriented guy, did this fairly quickly as a demonstration for coworkers. It required only marginally more than script kiddie levels of knowledge.
- lstamour 13y ago
  On Mac you can get the encryption key from RAM too, though if you turn on some settings, you can force the Mac to attempt a shutdown when it sleeps, clearing the encryption key until you enter your password later. There's still a DMA leak at startup also, but securing the EFI firmware helps keep things locked down. There was an article on HN recently with step by step instructions on scanning memory for things that look like AES keys when using TrueCrypt. I suspect without a Yubikey or Microsoft TPM, effectively storing the key outside of RAM, there's not much that can be done to fight this. And of course, physical access means you've got the TPM or Yubikey in front of you. And unencrypted data in RAM. So.... Yeah.
  - giovannibajo1 13y ago
    Actually, there are solutions to store the keys in CPU privileged registers (eg: hw debug registers), and when combined with AES-NI don't even cause much overhead: http://en.m.wikipedia.org/wiki/TRESOR http://en.m.wikipedia.org/wiki/TRESOR Not sure why these techniques aren't mainstream yet.
gizmo686 13y ago
Even without this type of PCI attack, you still have to worry about a cold boot attack. This is were the attacker quickly power-cycles the computer to boot into another OS (or special purpose boot code), and performs a memory dump. Often times the power cycles quickly enough that useful amounts of data remain in the RAM. This attack can be made more effective if you can get physical access to the RAM and cool it. As most (if not all) disk encryption programs store an expanded version of the key in memory, there is significant redundancy to recover from the partially lost data.
- coldtea 13y ago
  >This is were the attacker quickly power-cycles the computer to boot into another OS (or special purpose boot code), and performs a memory dump. Often times the power cycles quickly enough that useful amounts of data remain in the RAM. This attack can be made more effective if you can get physical access to the RAM and cool it. Has anybody ever did this to someone? Outside of Bond movies?
  - gizmo686 13y ago
    https://citp.princeton.edu/research/memory/ https://citp.princeton.edu/research/memory/ A few years ago, I tried this on my own laptop. I didn't have any sort of full disk encryption to test against, so I simply checked the RAM dump for plaintext looking things. Without having cooled the RAM (or opened the computer at all), there was a significant amount of meaningful plain-text. If you are interested in actual data about how effective this is, you should probably ignore my antecedent and look at the research paper in the above link. Given how easy this attack is for its effectiveness, I would be suprised if it is not used.
  - EvanAnderson 13y ago
    It has been demonstrated publicly. http://www.youtube.com/watch?v=Y_70UC0tPUU http://www.youtube.com/watch?v=Y_70UC0tPUU
mike_esspe 13y ago
You should always hibernate to crypted partition, when you are away from you computer. With modern SSD it's fast.
- ge0rg 13y ago
  You should never leave a sensitive device like your laptop unattended. A sophisticated attacker can replace your bootloader with a backdoored version that stores the encryption paraphrase to disk in plain.
  - giovannibajo1 13y ago
    That's what safe boot is for. You can't do this on a chrome book or a windows 8 laptop which is safe boot locked.

MichaelGG 13y ago

On OSX, IIRC, FireWire DMA was disabled if full disk encryption is turned on. Windows similarly has some sort of security advisory or capability wrt FireWire. If other ports are exposed that offer DMA capabilities, then they need to be disabled. Don't load the drivers/epoxy the physical ports. I was not aware that a new connector would reopen such a massive vulnerability. (Docking ports may also have some issue, but since they're proprietary it wouldn't matter.) That said, I think my assessment is still accurate. If you're just worried about a theft, it seems very unlikely they'd run these kinds of tools before restarting. And even then, why bother? Why not just reformat the machine, if it's just a theft? If you have actual enemies "then keep your laptop physically secured and powered off. And don't use it after breaking chain of custody." The really shitty thing is that some new laptops (W540) apparently don't ship DisplayPort or other digital video, but just Thunderbolt.

c0nsumer 13y ago

What's even niftier is, say with Windows and BitLocker, the BitLocker key can be recovered from a memory dump pulled this way. Couple this with live patching of RAM to bypass the lock screen and you're just kinda sunk. And yes, me, a not particularly security-oriented guy, did this fairly quickly as a demonstration for coworkers. It required only marginally more than script kiddie levels of knowledge.

lstamour 13y ago
On Mac you can get the encryption key from RAM too, though if you turn on some settings, you can force the Mac to attempt a shutdown when it sleeps, clearing the encryption key until you enter your password later. There's still a DMA leak at startup also, but securing the EFI firmware helps keep things locked down. There was an article on HN recently with step by step instructions on scanning memory for things that look like AES keys when using TrueCrypt. I suspect without a Yubikey or Microsoft TPM, effectively storing the key outside of RAM, there's not much that can be done to fight this. And of course, physical access means you've got the TPM or Yubikey in front of you. And unencrypted data in RAM. So.... Yeah.
- giovannibajo1 13y ago
  Actually, there are solutions to store the keys in CPU privileged registers (eg: hw debug registers), and when combined with AES-NI don't even cause much overhead: http://en.m.wikipedia.org/wiki/TRESOR http://en.m.wikipedia.org/wiki/TRESOR Not sure why these techniques aren't mainstream yet.

gizmo686 13y ago

Even without this type of PCI attack, you still have to worry about a cold boot attack. This is were the attacker quickly power-cycles the computer to boot into another OS (or special purpose boot code), and performs a memory dump. Often times the power cycles quickly enough that useful amounts of data remain in the RAM. This attack can be made more effective if you can get physical access to the RAM and cool it. As most (if not all) disk encryption programs store an expanded version of the key in memory, there is significant redundancy to recover from the partially lost data.

coldtea 13y ago
>This is were the attacker quickly power-cycles the computer to boot into another OS (or special purpose boot code), and performs a memory dump. Often times the power cycles quickly enough that useful amounts of data remain in the RAM. This attack can be made more effective if you can get physical access to the RAM and cool it. Has anybody ever did this to someone? Outside of Bond movies?
- gizmo686 13y ago
  https://citp.princeton.edu/research/memory/ https://citp.princeton.edu/research/memory/ A few years ago, I tried this on my own laptop. I didn't have any sort of full disk encryption to test against, so I simply checked the RAM dump for plaintext looking things. Without having cooled the RAM (or opened the computer at all), there was a significant amount of meaningful plain-text. If you are interested in actual data about how effective this is, you should probably ignore my antecedent and look at the research paper in the above link. Given how easy this attack is for its effectiveness, I would be suprised if it is not used.
- EvanAnderson 13y ago
  It has been demonstrated publicly. http://www.youtube.com/watch?v=Y_70UC0tPUU http://www.youtube.com/watch?v=Y_70UC0tPUU

mike_esspe 13y ago

You should always hibernate to crypted partition, when you are away from you computer. With modern SSD it's fast.

ge0rg 13y ago
You should never leave a sensitive device like your laptop unattended. A sophisticated attacker can replace your bootloader with a backdoored version that stores the encryption paraphrase to disk in plain.
- giovannibajo1 13y ago
  That's what safe boot is for. You can't do this on a chrome book or a windows 8 laptop which is safe boot locked.