Computer scientists have discovered a novel way to bypass the encryption used in programs like Microsoft’s BitLocker and Apple’s FileVault and then view the contents of supposedly secure files.
In a paper (PDF) published Thursday that could prompt a rethinking of how to protect sensitive data, the researchers describe how they can extract the contents of a computer’s memory and discover the secret encryption key used to scramble files.
“There seems to be no easy remedy for these vulnerabilities,” the researchers say. “Simple software changes are likely to be ineffective; hardware changes are possible but will require time and expense; and today’s Trusted Computing technologies appear to be of little help because they cannot protect keys that are already in memory. The risk seems highest for laptops, which are often taken out in public in states that are vulnerable to our attacks. These risks imply that disk encryption on laptops may do less good than widely believed.”
Scary stuff, what frightens me even more is they figures out how to remove the RAM from a machine without it loosing it’s state
Well, not so fast. Another interesting technique that Thursday’s paper describes is how to supercool the RAM chips with a can of compressed air held upside-down. Then the cooled memory can be physically extracted and inserted in another computer owned by the attacker. (If the memory is permanently affixed to the motherboard, there are still other methods [PDF] that can be used.)
The paper states:
Contrary to the expectation that DRAM loses its state quickly if it is not regularly refreshed, we found that most DRAM modules retained much of their state without refresh, and even without power, for periods lasting thousands of refresh intervals. At normal operating temperatures, we generally saw a low rate of bit corruption for several seconds, followed by a period of rapid decay. We obtained surface temperatures of approximately ?50 degrees C with a simple cooling technique: discharging inverted cans of “canned air” duster spray directly onto the chips. At these temperatures, we typically found that fewer than 1% of bits decayed even after 10 minutes without power. To test the limits of this effect, we submerged DRAM modules in liquid nitrogen (ca. ?196 degrees C) and saw decay of only 0.17% after 60 minutes out of the computer.
Gutmann, the New Zealand computer scientist, previewed this kind of attack in a 1996 paper that said: “To extend the life of stored bits with the power removed, the temperature should be dropped below -60 degrees C. Such cooling should lead to weeks, instead of hours or days, of data retention.”
Holy crap. Wish I had the time to actually try this, would be involving a good amount of hackery.
Translation: If you use an encrypted file-system and want privacy and security when you’re not using your computer, you need to shut down your computer and wait a few minutes for the RAM contents to vanish. Another option for sensitive files is to use an encrypted volume like a PGP disk and unmount it as soon as you’re done.
Something very important to take away from this is Sleep/Hibernate is very BAD. This makes me laugh at all those Apple fanboys that keep on saying I never turn of my machine, just put my Mac to sleep and when I need open it again. I will says thanks to Microsoft for the unreliabilty of their sleep technology I never (well almost never) use the sleep function if I am in motion. The only time I use sleep is when at home with my Macbook close by, not out of sight
I will be looking for some tools that can assist with wiping memory to prevent these “exploits” from actually working.
Me being clever: I doubt whether “Use Secure Virtual Memory” will help as that only works for the “Virtual Memory”, not RAM. What is needed is something that can encrypt the RAM before going to sleep and then put the machine in Deep Sleep with its suspend file encrypted. To wake up in this case should require dual authentication like biometric, smart card, usb dongle and a user/password maybe.