San Francisco - A team including the Electronic Frontier Foundation (EFF), Princeton University, and other researchers have found a major security flaw in several popular disk encryption technologies that leaves encrypted data vulnerable to attack and exposure.

"People trust encryption to protect sensitive data when their computer is out of their immediate control," said EFF Staff Technologist Seth Schoen, a member of the research team. "But this new class of vulnerabilities shows it is not a sure thing. Whether your laptop is stolen, or you simply lose track of it for a few minutes at airport security, the information inside can still be read by a clever attacker."

The researchers cracked several widely used disk encryption technologies, including Microsoft's BitLocker, Apple's FileVault, TrueCrypt, and dm-crypt. These "secure" disk encryption systems are supposed to protect sensitive information if a computer is stolen or otherwise accessed. However, in a paper and video published on the Internet today, the researchers show that data is vulnerable because encryption keys and passwords stored in a computer's temporary memory -- or RAM -- do not disappear immediately after losing power.

"These types of attacks were often thought to be in the realm of the NSA," said Jacob Appelbaum, an independent computer security researcher and member of the research team. "But we discovered that on most computers, even without power applied for several seconds, data stored in RAM seemed to remain when power was reapplied, We then wrote programs to collect the contents of memory after the computers were rebooted."

Laptops are particularly vulnerable to this attack, especially when they are turned on but locked, or in a "sleep" or "hibernation" mode entered when the laptop's cover is shut. Even though the machines require a password to unlock the screen, the encryption keys are already located in the RAM, which provides an opportunity for attackers with malicious intent.

The research released today shows that these attacks are likely to be effective against many other disk encryption systems because these technologies have many architectural features in common. Servers with encrypted hard drives are also vulnerable.

"We've broken disk encryption products in exactly the case when they seem to be most important these days: laptops that contain sensitive corporate data or personal information about business customers," said J. Alex Halderman, a Ph.D. candidate in Princeton's computer science department. "Unlike many security problems, this isn't a minor flaw; it is a fundamental limitation in the way these systems were designed."

In addition to Schoen, Appelbaum, and Halderman, the research team included William Paul of Wind River Systems, and Princeton graduate students Nadia Heninger, William Clarkson, Joseph Calandrino, Ariel Feldman as well as Princeton Professor Edward Felten, the director of the Center for Information Technology Policy and a member of EFF's Board of Directors.

The researchers have submitted the paper for publication and it is currently undergoing review. In the meantime, the researchers have contacted the developers of BitLocker, which is included in some versions of Windows Vista, Apple's FileVault, and the open source TrueCrypt and dm-crypt products, to make them aware of the vulnerability. One effective countermeasure is to turn a computer off entirely, though in some cases even this does not provide protection.

For the full paper "Lest We Remember: Cold Boot Attacks on Encryption Keys," a demonstration video, and other background information:


Seth Schoen
Staff Technologist
Electronic Frontier Foundation

Jacob Appelbaum
Computer Security Researcher

J. Alex Halderman
Princeton University

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