Supporting reliable data deletion for NAND-based gadgets with limited memory

As private and confidential data are now massively produced in mobile gadgets, managing them securely is becoming important. For instance, it should not be possible to restore deleted secure data, even when the gadgets are hacked through unauthorized access. The existing tools operating on hard disks guarantee reliable data deletion by overwriting secure files multiple times. However, this method does not operate correctly in mobile gadgets using NAND flash memory as storage media, because they apply out-of-place update and the old data remain unmodified even when overwritten. To address this problem while incurring only a low overhead, in this paper the design of a reliable data deletion scheme based on the hybrid mapping flash translation layer that delivers high performance with low memory usage is described. The basic concept is to count the overwrite operations of a logical block and eliminate all the old data when the count exceeds a threshold. The high scattering degree of a logical block that causes a significant overhead of erasing the old data is mitigated by adopting an active log pool. A trace-driven evaluation shows that the proposed scheme delivers a 12.4-22.3% better performance than that of an existing scheme that supports reliable data deletion. The additional memory consumption is 512 KB in a 32 GB partition and 1.12 MB in a 70 GB partition, which is not significant.