Research On Per-file Secure Deletion For Flash-Based Solid State Drives

Due to the out-of-place update feature of Solid State Drives(SSD),file update operations generate many invalid flash pages within the SSD that store file expiration data.If these invalid flash pages are not securely deleted in real time,they will be left in the "missing" state on the storage medium,resulting in leakage of sensitive information.However,if they are securely deleted in real time,the performance of the SSD will be greatly reduced.In order to achieve non-real-time secure deletion of per-file,it is necessary to maintain the correspondence between the invalid data blocks and the invalid backup files and the original file,so that when the file is deleted,they are securely deleted together with the data blocks of the file.Aiming at invalid blocks of the file,a Per-File Secure Deletion(PSD)based on SSD is proposed.A globally unique identifier(GUID)is assigned to each file,in the device layer,each data block of the file is associated with the file GUID,so that the storage location where the invalid data blocks corresponding to the file is located can be quickly found.At the same time,the file system is provided with a Security-TRIM command to securely delete data blocks and invalid data blocks of a file meanwhile when the file is deleted.Further,for editor applications,providing a secure deletion scheme for invalid backup files named(PSD-E),associating the invalid backup files with the original file,when the original file is deleted,the invalid backup files are securely deleted together.In particular,due to the use of overwrite technology to implement secure deletion,when overwriting the data in a single page of the paired pages of Multi-Level Cell(MLC)flash memory,the data in the paired pages occur error.So a pair page allocation scheme named PSD-MLC is proposed to distribute the data blocks of the file in pairs of pages so that the paired pages corresponding to the file are securely deleted together when the file is securely deleted,thereby avoiding the influence of programming crosstalk between paired pages.By testing on different hardware platforms of flash media,the test results prove that the PSD and PSD-MLC solution have little impact on the performance of solid state drives.When disabling and enabling of the cache,compared with the system without the secure deletion,PSD decreases SSD throughput by 1.3% and 1.8% respectively,and PSD-MLC decreases SSD throughput by 9.5% and 10.0% respectively.Compared with the secure deletion schemes which deleting invalid flash pages in real time,PSD increases SSD throughput by 44.7% and 45.4% respectively.In addition,because PSD-MLC reduces the overhead of migrating a valid flash page in a pair of pages,increaseing SSD throughput by 198% and 180%,respectively.