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2/21/2011
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SSDs Prove Tough To Erase

Techniques that reliably erase hard disk drives don't produce the same results for solid state drives, warn University of California at San Diego researchers.

Solid state drives (SSDs) have a small security problem: they're tough to erase.

That warning comes from researchers at the University of California at San Diego. "Sanitization is well-understood for traditional magnetic storage, such as hard drives and tapes," said the researchers' in their study summary. "Newer solid state disks, however, have a much different internal architecture, so it is unclear whether what has worked on magnetic media will work on SSDs as well."

Accordingly, the researchers tried 14 different file sanitizing techniques -- ranging from Gutman's 35-pass method to the Schneier 7-pass method -- on SSDs. To study each technique's effectiveness, the researchers didn't query the flash translation layer (FTL) that's part of an SSD, but rather accessed the chips at the lowest level possible, via their pins. (Dismantling chips is straightforward, they said.)

What they found is that every data-erasing technique left at least 10MB of recoverable data from a 100MB file. Some techniques, such as overwriting the chip with pseudorandom data or using a British HMG IS5 baseline, left nearly all data intact.

By any measure, SSDs aren't the dominant way of storing data today, but their use is increasing. According to the recent InformationWeek Analytics State of Enterprise Storage Survey, nearly one-quarter of organizations have deployed SSDs in their data center, and more than half plan to either initiate or increase their use of SSDs this year.

Meanwhile, storage market researcher iSuppli predicts that the SSD penetration rate for laptops will increase from roughly 2% in 2010 to nearly 8% by 2014.

But according to the University of California at San Diego researchers, businesses must beware how they handle SSDs, because it's tough to erase data from them. "Our results show that naïvely applying techniques designed for sanitizing hard drives on SSDs, such as overwriting and using built-in secure erase commands is unreliable and sometimes results in all the data remaining intact," they said. "Furthermore, our results also show that sanitizing single files on an SSD is much more difficult than on a traditional hard drive."

How can SSDs be effectively secured or disposed of, short of physically destroying them? The researchers propose encrypting all data from the start, then destroying the encryption keys and overwriting every page of data to securely wipe the SSD and block future key recovery.

Implementing such an approach requires planning. "To properly secure data and take advantage of the performance benefits that SSDs offer, you should always encrypt the entire disk and do so as soon as the operating system is installed," said Chester Wisniewski, a senior security advisor for Sophos Canada, in a blog post. Based on the researchers' findings, "securely erasing SSDs after they have been used unencrypted is very difficult, and may be impossible in some cases," he said.

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