Who will be the last HD maker down the road?

Eric Smith eric at brouhaha.com
Wed Mar 9 14:46:24 CST 2011

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.


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