Think again. Ed Felten has made an interesting discovery:

Today eight colleagues and I are releasing a significant new research result. We show that disk encryption, the standard approach to protecting sensitive data on laptops, can be defeated by relatively simple methods. We demonstrate our methods by using them to defeat three popular disk encryption products: BitLocker, which comes with Windows Vista; FileVault, which comes with MacOS X; and dm-crypt, which is used with Linux. The research team includes J. Alex Halderman, Seth D. Schoen, Nadia Heninger, William Clarkson, William Paul, Joseph A. Calandrino, Ariel J. Feldman, Jacob Appelbaum, and Edward W. Felten.

Our site has links to the paper, an explanatory video, and other materials.

The root of the problem lies in an unexpected property of today’s DRAM memories. DRAMs are the main memory chips used to store data while the system is running. Virtually everybody, including experts, will tell you that DRAM contents are lost when you turn off the power. But this isn’t so. Our research shows that data in DRAM actually fades out gradually over a period of seconds to minutes, enabling an attacker to read the full contents of memory by cutting power and then rebooting into a malicious operating system.

Interestingly, if you cool the DRAM chips, for example by spraying inverted cans of “canned air” dusting spray on them, the chips will retain their contents for much longer. At these temperatures (around -50 °C) you can remove the chips from the computer and let them sit on the table for ten minutes or more, without appreciable loss of data. Cool the chips in liquid nitrogen (-196 °C) and they hold their state for hours at least, without any power. Just put the chips back into a machine and you can read out their contents.

This is deadly for disk encryption products because they rely on keeping master decryption keys in DRAM…

Bet this won’t stop Gordon Brown & Co confidently asserting that our data are safe in their laptops.