Princeton scientists crack disk encryption
A team of academic, industry and independent researchers has demonstrated a new class of computer attacks that compromise the contents of secure memory systems, particularly in laptops
The attacks overcome a broad set of security measures called "disk encryption," which are meant to secure information stored in a computer's permanent memory. The researchers cracked several widely used technologies, including Microsoft's BitLocker, Apple's FileVault and Linux's dm-crypt, and described the attacks in a paper and video published on the Web Feb. 21.
The team reports that these attacks are likely to be effective at cracking many other disk encryption systems because these technologies have architectural features in common.
"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 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."
The attack is particularly effective against computers that are turned on but are locked, such as laptops that are in a "sleep" or hibernation mode. One effective countermeasure is to turn a computer off entirely, though in some cases even this does not provide protection.
Halderman's Princeton collaborators included graduate students Nadia Heninger, William Clarkson, Joseph Calandrino, Ariel Feldman and Professor Edward Felten, the director of the Center for Information Technology Policy. The team also included Seth Schoen of the Electronic Frontier Foundation, William Paul of Wind River Systems and independent computer security researcher Jacob Appelbaum.
Felten said the findings demonstrate the risks associated with recent high-profile laptop thefts, including a Veterans Administration computer containing information on 26 million veterans and a University of California, Berkeley laptop that contained information on more than 98,000 graduate students and others. While it is widely believed that disk encryption would protect sensitive information in instances like these, the new research demonstrates that the information could easily be read even when data is encrypted.
"Disk encryption is often recommended as a magic bullet against the loss of private data on laptops," Felten said. "Our results show that disk encryption provides less protection than previously thought. Even encrypted data can be vulnerable if an intruder gets access to the laptop."
The new attacks exploit the fact that information stored in a computer's temporary working memory, or RAM, does not disappear immediately when a computer is shut off or when the memory chip is taken from the machine, as is commonly thought. Under normal circumstances, the data gradually decays over a period of several seconds to a minute. The process can be slowed considerably using simple techniques to cool the chips to low temperatures.
