and government offices are constantly replacing computers and buying new
hardware. Typically when this is done, data on the hard drives of the
defunct machines is wiped, lest it fall
into the wrong hands.
However, an intriguing study [press release] by researchers at the University
of California San Diego (UCSD) reveals that businesses thinking
they've wiped NAND thumb drives or NAND solid-state drives (SSDs) may be in for
Every time you write to a hard drive -- be it magnetic disk or NAND -- you make
semi-permanent changes that persist until you overwrite that block of memory.
When you delete files on your computer, you typically are merely deleting
the indexes of the files. The actual data persists on the drive until you
Over a dozen methods have been worked
out to try to fully overwrite data on a magnetic hard drive and permanently
erase any traces of the drive's original contents. Researchers tried
those methods on flash drives and discovered that, at best, they left 10 MB of
every 100 MB file intact.
To study how successful the data destruction was, the researchers took apart an
SSD. Rather than check the Flash Translation Layer (FTL), which would
merely show data as indexed by the drive, they actually sliced out the physical
chips and queried them via their pins. This allowed them to test the data
status at the lowest level.
The findings might shock some, but came as little surprise to the researchers
who expected magnetic drive techniques to work less than optimally for SSDs.
Some of the techniques attempted, such as Gutman's 35-pass method, Schneier
7-pass method, erased as much as 90 percent of data successfully. But
other techniques, like using pseudorandom numbers to overwrite data on the chip
or using a British HMG IS5 baseline, left virtually the entire file intact.
Researchers Laura Grupp and Michael Wei comment, "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. Furthermore, our results
also show that sanitizing single files on an SSD is much more difficult than on
a traditional hard drive."
Of course, if you encrypt all the data
on the SSD to start, you make it harder to access. The
researchers note this and suggest that to completely prevent data loss, users
then destroy their keys and use new technology to directly overwrite all of the
Chester Wisniewski, a senior security advisor for Sophos Canada, blogged on the study
praising its accuracy. He writes, "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... [S]ecurely erasing SSDs after they have been used unencrypted is
very difficult, and may be impossible in some cases."
These results are not only troubling for business and government users, but for
home users as well. You have plenty of things to worry about falling into
the wrong hands -- personal emails from your family; credit card records;
medical records; and other private info. At present, you can't be 100
percent sure you can securely dispose of SSDs with this kind of information,
but by using encryption you can reduce the likelihood of someone get your
information to almost zero.
According to a recent iSuppli report,
only 2 percent of laptops currently carry SSDs. However, iSuppli predicts
that by 2014, that total will rise to 8 percent.