Cold Boot attacks on disk encryption

The Centre for Information Technology Policy at Princeton University has released research which shows a potential way of breaking encryption systems by reading DRAM contents even after power has been removed.

The Abstract reads

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.

Their website contains a video demonstration of the technique as well as a link to the full research document (pdf)

Obviously this isn't limited just to breaking disk encryptions as all manner of information could be held in RAM at any one time. DRAM is composed of capacitors that need to keep being refreshed dynamically while being used it is this capacitance that is being exploited in this hack.

From the Freedom To Tinker Blog