  NAND flash memory-based IoT device can potentially still leave behind
original personal data in an invalid area even if the data has been deleted. In
this paper, we raise the forensic issue of original data remaining in unmanaged
blocks caused by NAND flash memory and introduce methods for secure deletion of
such data in the invalid area. We also propose a verification technique for
secure deletion that is performed based on cell count information, which refers
to the difference in bits between personal data and data stored in the block.
The pass/fail of the verification technique according to the cell count
information is determined in consideration of error correction capabilities.
With the forensic issue of de-identification being a vital theme in the big
data industry, the threat of serious privacy breaches coupled with our proposal
to prevent these attacks will prove to be critical technological necessities in
the future.
