9 Mar
2011
9 Mar
'11
12:46 p.m.
Richard wrote:
Flash memory is problematic for secure data.
Basically, its nearly
impossible to securely erase a file from flash based disks.
vintagecoder at aol.com wrote:
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?
That's *exactly* the problem. It doesn't. dd only fills the blocks
that are currently in use, but the card may have spared out marginal
blocks that still contain residual user data. After that happens, there
is no normal command to the device that provides access to those blocks,
though there may be vendor-unique ways to get at them, and a well-funded
adversary almost certainly could recover that data.
This is true of modern hard drives as well.
That's why the "secure erase" commands were added to the ATA command
set, and the drive is supposed to erase even the spared blocks.
Eric