Rosio Pavoris

So I probably should too.
This video describes a simple but effective attack again whole disk encryption and similar cryptosystems, based on the fact that, contrary to popular belief, modern DRAM retains its data for some time after power is cut, and the encryption key is stored in said DRAM.

There’s some more information in the full paper.

There are some obvious ways to defend against this as a user. One is to not leave your computer unattended while you’re logged in, or for several minutes after you’ve logged out and powered down.
The former should be obvious, but isn’t, and BitLocker’s thing that lets you boot straight to log-in makes it less than straightforward. Though if you use Vista, chances are you’re only doing the encryption thing because your boss made you anyway, and you don’t care about security or privacy.
Basically, if you aren’t typing the encryption password as well as your account password every time you boot, you have a problem.

It shouldn’t be too difficult to have the OS or some hardware device clear the entire RAM (or just a given area of it) as soon as a power failure is detected (it can keep running for a few milliseconds after the PSU sends the power failure signal, which is still a few thousand clock cycles), but that would be just as easy to get around, so it’s not worth the effort.

Another option is to just not store the key in RAM, but in a CPU register or the cache or something. I’m not sure how long their retain their information, but presumably it’s not nearly as long; possibly short enough to prevent this attack.
Of course, keeping something in the cache or the registers all the time isn’t something most OSes will play nice with, so that will require some OS-level retooling, and encryption keys tend to be comparatively large (128 to 256 bits may not seem like a lot, but a CPU register is 32 or 64 bits wide nowadays, and there aren’t that many of them), so that’s only going to increase the performance hit of whole disk encryption (which isn’t as big as people expect, but big enough that you don’t want to increase it).

The easiest thing is just to keep people away from your precious RAMs.