Partial disk encryption leakage

There is some talk out there about how partial disk encryption products are leaky because of how Word and other programs handle the documents when they access them. Basically, they often pull the documents into an unencrypted space when working with the files, and they can be recovered from that space. Full disk encryption does not have this issue because, as it is named, the entire disk is encrypted.

One of the quotes from the article comes from Tadayoshi Kohno, an assistant professor at the University of Washington in Seattle who co-authored the study:

He believes that there are probably many other applications and operating system components that leak out information in a similar way. "I suspect that this is a potentially huge issue. We've basically cracked the surface," he said.

Another quote from the article:

Nobody really knows how much data can be recovered from a partially encrypted disk, but the researchers say that they were able to recover copies of most of the Word documents created for their experiment from the software's auto-recovery folder, even though the documents themselves were being saved to an encrypted part of the disk. "We just don't know how much data is leaking out but it's enough to be worried about," Kohno said.

With Google Desktop, the researchers were able to read snapshots of encrypted files when the program's Enhanced Search option was enabled.

I don't know how pristine the conditions were here, but it clearly shows this as a valid attack. And I don't get the feeling that this is FUD (unless Mr. Kohno has shares in full disk encryption companies). So in that respect, and coupled with the risk factor, I think this is MUCH more of an issue than the keys getting stored in RAM.

I also don't see this being an easy fix. One of the partial encryption products I have evaluated takes care of the keys in RAM issue by simply wiping them out each time the PC / laptop changes state into hibernation, power off, etc. So you have to enter a password each time you change back into an active state so the key can be generated each time (it uses a lot of factors to do this). The password each time can be annoying, but it is definitely a simple and effective means of protecting the key. But how do you fix this issue when the basic problem is not with the encryption product but with how other programs interact with the encryption?

If someone knows of any partial-disk encryption products that handle this, please let me know. But for now, my recommendation would be to use full disk encryption.


Copyright © 2008 IDG Communications, Inc.

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