Cold Reboot Attacks on Disk Encryption

jcrouthamel writes "Contrary to popular assumption, DRAMs used in most modern computers retain their contents for seconds to minutes after power is lost, even at operating temperatures and even if removed from a motherboard. Although DRAMs become less reliable when they are not refreshed, they are not immediately erased, and their contents persist sufficiently for malicious (or forensic) acquisition of usable full-system memory images. We show that this phenomenon limits the ability of an operating system to protect cryptographic key material from an attacker with physical access. We use cold reboots to mount attacks on popular disk encryption systems — BitLocker, FileVault, dm-crypt, and TrueCrypt — using no special devices or materials. We experimentally characterize the extent and predictability of memory remanence and report that remanence times can be increased dramatically with simple techniques. We offer new algorithms for finding cryptographic keys in memory images and for correcting errors caused by bit decay. Though we discuss several strategies for partially mitigating these risks, we know of no simple remedy that would eliminate them."

Comments

Re:Clear the DRAM?

[theaveng]

For this to work, somebody has to be able to steal my laptop, hack the double-password system, and get Windows up-and-running. Only then can they apply this "power off/power up" method of copying my RAM.

I am not concerned; they'd have a difficult time guessing both passwords. And with the program I use (or rather the government uses), the hard drive is hard formatted after 10 incorrect guesses, leaving behind no information.

I feel secure.

However, I can see this as an effective method to steal other keys... like the Blu-ray key out of PowerDVD.