Who will be the last HD maker down the road?

[Joachim Thiemann]

On Wed, Mar 9, 2011 at 14:46,  <vintagecoder at aol.com> wrote:
>> Flash memory is problematic for secure data.  Basically, its nearly
>> impossible to securely erase a file from flash based disks.
>
> I don't know how that can be true. I can understand deleting doesn't work
> but is it true a simple dd if=/dev/zero of=/dev/sdx onto the flash card
> doesn't fill it with zeros? And even if it doesn't, how hard is a flash
> card to destroy? Hard disks are tough as nails but flash memory can be
> snapped in two with your hands or a pair of pliers and burned...

Writing a '0' to a location of the flash that used to be '1' MIGHT
leave the internal analogue state at a higher level than if the bit
previously was '0'.  If you then operate the flash in abnormal
conditions (messing with the supply voltages) you MAY be able to get
the memory into a state where the reading thresholds are "just right"
to get the old state.

Of course, chances that anyone will actually try to steal your data
that way are close enough to 0 that if you are the kind of person to
be paranoid about those things you'd use easier ways to introduce
large amounts of entropy to the chip.

Going back on-topic (is data recoverable?) I'd say the bit-error rate
of the above method is probably way too high to rely on this as a
backup strategy.

Joe.

-- 
Joachim Thiemann :: http://www.tsp.ece.mcgill.ca/~jthiem