A friend has sent me a link to a paper/video that describes cold boot attacks on encryption keys. Here is an excerpt from the paper’s abstract:

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.

If you would like to read the complete report, go to the “Lest We Remember: Cold Boot Attacks on Encryption Keys” webpage which contains the complete report and a video that explains the vulnerability.