4 ms·

Before you dive too far into full-disk encryption, you might want to contemplate the consequences of this research: http://news.cnet.com/8301-13578_3-9876060-3

by all 16y ago

Before you dive too far into full-disk encryption, you might want to contemplate the consequences of this research: http://news.cnet.com/8301-13578_3-9876060-38.html http://news.cnet.com/8301-13578_3-9876060-38.html The paper referenced is available at: http://citp.princeton.edu/pub/coldboot.pdf http://citp.princeton.edu/pub/coldboot.pdf From that paper, the most salient sentence for this discussion is: "On all of our sample DRAMs, the decay rates were low enough that an attacker who cut power for 60 seconds would recover 99.9% of bits correctly." The long and short is that your password has to be in RAM at some point in order to be matched against what is typed in. RAM decays slowly after a machine has been switched off. As the research shows, one can use a widely-available can of air to make that decay happen even slower. In the process, one can pull the value out of RAM. Note that this is a hardware problem that no software on the market has been able to address. To do so, you would have to be able to validate x against y without having the value of y ever enter RAM. Consequently, a reasonably good tech thief can read the password out of RAM. For the not-so-good tech thief, using passwords and social engineering tricks like being nice to someone and then asking them to watch your stuff for a moment will probably do the trick. I tend to see the various implementations of full-disk encryption as more for peace of mind and mitigation of liability than real security.

thibaut_barrere 16y ago
There are always way to hack a computer: but we're just asked to take reasonable steps toward making it harder.
- edanm 16y ago
  Yes, but that's exactly why it's important to realize this only gives you some protection. The OP asked for his personal needs, not because of some company policy, which means he/she should know whether it really is effective.
tptacek 16y ago
Remanence isn't a realistic attack in his threat model; attackers have mere minutes to get the RAM out of his system, cool it, and siphon the data off. If he's worried about losing the Plans to the Empire when his ship is captured, sure. But if he leaves his bag in the back of a cab, he'll be fine. The notion that any "reasonably good tech thief" could pull this off is also hard to take seriously. So far as I know, there are zero (0) remanence key extractor tools in circulation. Highly skilled attackers --- many apparently in the employ of foreign governments --- have a hard enough time writing tools to extract keys from live memory.
- all 16y ago
  The threat is not against the Plans to the Empire but the password for the encryption system. That, as the video shows, can be done and without any particular haste. As the article suggests, freezing the RAM lengthens the decay process. The method is likely to have been known by three-letter agencies for some time now. The good guys are seldom, if ever, ahead of the bad guys, so it seems likely that the latter know it, too. But, for the sake of argument, let's say that they don't crack it on the first go. So what? The password has to be in RAM every time the machine starts. AFAIK (and I would be pleased to be wrong about this), nobody shreds data on the hard drive because the user gets their password wrong. So, said bad guys can try to their heart's content. As far as I'm concerned, it is a major hole in any argument for full-disk encryption.
  - tptacek 16y ago
    I think you're misunderstanding both the attack and full-disk encryption. The decryption key is not in RAM every time the machine starts; you have to enter material to derive the key at bootup. And the attacker does in fact have minutes to recover whatever's in RAM once the machine shuts down --- which means that if you shut your machine down before leaving the office (which you have to do), remanence simply isn't a threat at all. Everyone "shreds" their hard disk if they lose the password. That is the point. Also, the Plans are to the Death Star, not the whole Empire.
    - nonane 16y ago
      Rarely does one shutdown a laptop anymore. Usually people just close the lid and the computer is put to sleep. In sleep state the contents of RAM is preserved AFAIK and should give the attacker more time to think their plan through.
      - tptacek 16y ago
        The rules are different when you use full-disk encryption. You shut your machine down. PGP WDE actually prevents "sleep" from working, but regardless, you still need to be vigilant.
runjake 16y ago
The poster mentions they wish to defend against theft and lost. The attacks you cite are more applicable if he were worried about intelligence agencies intercepting his data. And with rumored incestuous relationships with the corporate world, that might not be a bad idea, if he has valuable IP.

by all 16y ago

thibaut_barrere 16y ago

There are always way to hack a computer: but we're just asked to take reasonable steps toward making it harder.

edanm 16y ago
Yes, but that's exactly why it's important to realize this only gives you some protection. The OP asked for his personal needs, not because of some company policy, which means he/she should know whether it really is effective.

tptacek 16y ago

Remanence isn't a realistic attack in his threat model; attackers have mere minutes to get the RAM out of his system, cool it, and siphon the data off. If he's worried about losing the Plans to the Empire when his ship is captured, sure. But if he leaves his bag in the back of a cab, he'll be fine. The notion that any "reasonably good tech thief" could pull this off is also hard to take seriously. So far as I know, there are zero (0) remanence key extractor tools in circulation. Highly skilled attackers --- many apparently in the employ of foreign governments --- have a hard enough time writing tools to extract keys from live memory.

all 16y ago
The threat is not against the Plans to the Empire but the password for the encryption system. That, as the video shows, can be done and without any particular haste. As the article suggests, freezing the RAM lengthens the decay process. The method is likely to have been known by three-letter agencies for some time now. The good guys are seldom, if ever, ahead of the bad guys, so it seems likely that the latter know it, too. But, for the sake of argument, let's say that they don't crack it on the first go. So what? The password has to be in RAM every time the machine starts. AFAIK (and I would be pleased to be wrong about this), nobody shreds data on the hard drive because the user gets their password wrong. So, said bad guys can try to their heart's content. As far as I'm concerned, it is a major hole in any argument for full-disk encryption.
- tptacek 16y ago
  I think you're misunderstanding both the attack and full-disk encryption. The decryption key is not in RAM every time the machine starts; you have to enter material to derive the key at bootup. And the attacker does in fact have minutes to recover whatever's in RAM once the machine shuts down --- which means that if you shut your machine down before leaving the office (which you have to do), remanence simply isn't a threat at all. Everyone "shreds" their hard disk if they lose the password. That is the point. Also, the Plans are to the Death Star, not the whole Empire.
  - nonane 16y ago
    Rarely does one shutdown a laptop anymore. Usually people just close the lid and the computer is put to sleep. In sleep state the contents of RAM is preserved AFAIK and should give the attacker more time to think their plan through.
    - tptacek 16y ago
      The rules are different when you use full-disk encryption. You shut your machine down. PGP WDE actually prevents "sleep" from working, but regardless, you still need to be vigilant.

runjake 16y ago

The poster mentions they wish to defend against theft and lost. The attacks you cite are more applicable if he were worried about intelligence agencies intercepting his data. And with rumored incestuous relationships with the corporate world, that might not be a bad idea, if he has valuable IP.