Hello,
I have been reviewing a number of applications for securing deleting files. I understand the concepts of overwriting the file several times with zeros and random characters; however, I don't understand the concept of renaming the file up to thirty times before actually deleting the file. Any feedback would greatly be appreciated.
I am currently working on a PCI DSS project.
URL - SDELETE by Sysinternals http://technet.microsoft.com/en-us/sysinternals/bb897443.aspx
Thanks, Brennan
Despite the data having being obscured by having been overwritten, simple removal of a file does not obliterate the directory entry associated with the file in the filesystem (e.g. NTFS). As evidenced in the link you posted, sometimes the directory entries for deleted files can still be hanging around in free space on NTFS.
So, because the file name itself may contain sensitive information, renaming the file multiple times helps obscure what the original name was. Though it is of course dependant on the implementation of the underlying filesystem.
Actually I do not have a direct answer to your question but you do not have to overwrite the data nor the FS-entry 30 times.
The german magazine for computer technics (c't) has published an article about a paper which handles this topic. The quintessence of the article is that overwriting the data once is enough.
The c't article (german): http://www.heise.de/newsticker/meldung/Sicheres-Loeschen-Einmal-ueberschreiben-genuegt-198816.html
Information about the paper (english): http://www.springerlink.com/content/408263ql11460147/
After all it should suffice to rename the file to /tmp/tmp_file (or so) and overwrite it with random data or zeros before deleting it.