File encryption poses security threat

Encrypted data, including files and documents that contain child pornography, bank account information or credit card numbers, may be accessible to a new breed of enterprising identity thieves and technology forensic experts, according to a study by a Princeton-led research group.

The group included computer science and public affairs professor Ed Felten, five University graduate students and three outside experts. The website for the University Center for Information Technology Policy (CITP) published a paper detailing the experiments and results last week.

“We got this idea from a 2005 Stanford paper,” said Felten, who is also director of the CITP. The paper suggested “that information might stay in memory longer than we thought, and we started thinking about what the security implications of that would be.”

Research methods and discoveries

Contrary to the popular belief that computer data disappears as soon as the power turns off, the research team found that information remains in computer memory chips for five to 45 seconds after shutting down. Information stored on the computer can be read directly off the memory chips. Cooling the chips with liquid nitrogen or compressed air can increase the retention of information from seconds up to several hours.

The biggest impact of the lingering data will be on the data- encryption methods used to protect the files on laptop computer hard drives, Felten said.

Computers, especially laptops, which are more easily lost or stolen, often include disc-encryption software. The software encrypts files on the hard drive so they cannot be viewed without accessing the encryption key stored in the computer’s memory. The research team discovered that the encryption key, which is a long series of bits (0s or 1s), could easily be retrieved from the memory chips of computers.

“The secret key that can decrypt everything is sitting in the computer’s memory chip, and because information can be captured from the memory chips, that means these encrypted files are not nearly as safe as people thought,” Felten explained.

A potential obstacle to finding the keys was distinguishing them from the other information stored on the chips, but the researchers found that the encryption keys were coded in very distinct, easily recognizable patterns and could be detected using a simple pattern-recognition program they wrote. Decryption methods and keys depend on the specific encryption process implemented on a computer, but the most common methods used in computers running Windows, Mac OS or Linux operating systems are all vulnerable to attack, Felten said.

Unexpected results

The results of the seven-month study were almost entirely unforeseen by members of the technology community, several of the team’s researchers said.

“For me, the most surprising finding was the simple fact that computer RAM retains its data for a noticeable period of time after power is cut,” researcher Ariel Feldman GS said. “Although some people were aware of this phenomenon before our paper was released, to my knowledge, it had never been studied extensively, and many, if not most, computer scientists didn’t know about it.”

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Fellow researcher Nadia Heninger GS said she was shocked by how easy it was to break the encryption programs.

“Once we started looking at the data in RAM, we discovered that every program had stored their keys in exactly the same way,” Heninger said. “It was actually easier to break the encryption than to install the programs in the first place.”

Surprisingly, many laptop computers also sacrifice useful security measures for the sake of user convenience, said Bill Paul, a senior engineer at software company Wind River Systems and a member of the research team.

“Many newer systems don’t default to performing destructive memory tests at start-up, and I think the reason for this has more to do with marketing than anything else,” Paul said. “With multi-gigabyte memory sizes becoming commonplace, skipping the test vastly reduces start-up time, and a quick start-up is considered beneficial for a pleasant ‘user experience.’ ”

Short-term impact

The research team’s discoveries may facilitate identity theft and access to information on stolen laptops, several members of the group said.

“Many average computer users might think that our findings don’t affect them because they don’t use disk encryption and don’t think that they have anything worth stealing on their hard drives,” Feldman said. “[But] even though it’s highly unlikely that an attacker would specifically target [their] computer, chances are that users’ personal data also resides on the hard disks of both government and private organizations.”

Researcher John Halderman GS said he was particularly concerned about the vulnerability of the financial data stored on bank and credit card company computers.

“A laptop with bank account numbers or credit card numbers for thousands of people is an enormous risk,” Halderman said. “The normal way people protect that information is disc encryption, and our discoveries open huge new avenues for identity theft.”

To better protect this kind of information, Halderman said, companies should store it exclusively on desktop machines, which are harder to lose or steal than laptops. If the information needs to be kept on laptops, Halderman added, others should be careful to always shut them off when not in use.

The discoveries may also enable criminals to retrieve encrypted information from stolen or lost laptops and allow computer forensics specialists to recover protected data, such as child pornography, for investigative purposes.

Long-term consequences

The computer-chip vulnerabilities exploited by the research team for data decryption may lead to long-term changes in machine software and hardware, researchers said.

The findings may spur the development of RAM chips that automatically self-erase when they detect that power has been turned off, tamper-resistant memory for storing encryption keys and software that encrypts the memory of laptops even when they are in sleep mode, Feldman said.

Paul said that it would be next to impossible for software vendors to guarantee complete protection against the kinds of attacks the researchers demonstrated because other software on the machine, sold by a different vendor, may be vulnerable.

“For example, if you leave your computer unattended and logged into AOL Instant Messenger, the AIM client might leave your username and password in memory,” Paul said. “If you use the same password for AIM as you do for other things, and I can recover it, I can use it to compromise all your accounts that use the same password. At the very least, I can pretend to be you on AIM.”

Though changes to software will be faster and easier to design than hardware ones, researcher Joseph Calandrino GS said he believed improved software security would not be sufficient.

“Variants, though perhaps less dangerous variants, of these attacks are likely to remain unless computer hardware is also changed,” Calandrino said.