Implementing secure file deletion in NANDbased block devices with internal buffers

The goal of this work is to support secure file deletion in NAND-based block devices with an internal buffer. Existing secure file deletion tools for hard disks overwrite the file contents many times, causing them to become distorted and irrecoverable. However, NAND-based block devices perform an out-of-place update on the overwrite request, meaning that the original data are preserved without modification and restorable. Furthermore, if there is an internal buffer, then this absorbs the overwrite request. Thus, the existing secure file deletion tools do not work properly in NAND-based block devices. In order to support secure file deletion, this work presents a modification of the internal buffer manager and the underlying flash translation layer. The buffer manager records the overwrite count of each logical page, and sends a request to permanently erase the secure data when the overwrite count exceeds a threshold. Upon receiving this request, the flash translation layer erases all of the old data on the target logical page. The performance overhead resulting from this secure file deletion is evaluated by a trace-driven simulation of representative flash translation layer schemes. The results show that the page mapping method delivers the best performance of the representative flash translation layer schemes, in spite of suffering significant performance degradation.