Secure data deletion for Linux file systems

Abstract

Security conscious users of file systems require that deleted information and its associated meta-data are no longer accessible on the underlying physical disk. Existing file system implementations only reset the file system data structures to reflect the removal of data, leaving both the actual data and its associated meta-data on the physical disk. Even when this information has been overwritten, it may remain visible to advanced probing techniques such as magnetic force microscopy or magnetic force scanning tunneling microscopy. Our project addresses this problem by adding support to the Linux kernel for asynchronous secure deletion of file data and meta-data. We provide an implementation for the Ext2 file system; other file systems can be accommodated easily. An asynchronous overwriting process sacrifices immediate security but ultimately provides a far more usable and complete secure deletion facility. We justify our design by arguing that user-level secure deletion tools are inadequate in many respects and that synchronous deletion facilities are too time consuming to be acceptable to users. Further, we contend that encrypting file information, either using manual tools or a encrypted file system, is not a sufficient solution to alleviate the need for secure data deletion.