If you’ve thought your data are secure on encrypted hard disk, read: Lest We Remember: Cold Boot Attacks on Encryption Keys. Researchers with Princeton University and the Electronic Frontier Foundation (EFF) have found a flaw that renders disk encryption systems useless if an intruder has physical access to your computer – say in the case of a stolen laptop or when a computer is left unattended on a desktop in sleep mode or while displaying a password prompt screen. The attack takes only a few minutes to conduct and uses the disk encryption key that’s stored in the computer’s RAM.
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.