-----BEGIN PGP SIGNED MESSAGE----- Hash: SHA1 September 13, 2003 10:18 am, Mathieu Frenette wrote:
Top posting because it's brief. The difference between "shredding" and deleting is a matter of degree. Wipe and overwrite _now_ versus wipe and overwrite whenever you get a "round-to-it." ;-) Any major university electronics lab with access to a scanning tunnelling electron microscope can almost always recover enough fragments of data to put together an overall picture from the "magnetic residue" left behind. Even from seized or otherwise damaged drives. That's what companies that offer data recovery services do. It takes major amounts of time and expensive equipment, and is not cheap. The NSA can do all sorts of magic if there's a reason. That reason would have to "make sense," especially "politically" since the Intelligence Oversight Committee would be crawling up their butts otherwise. Which for the drives of most of us (home and small business users) it wouldn't. So the question becomes: "Of course I'm paranoid, but am I paranoid *enough?*" C. > Hi! > > > Why 20 times? How is it possible to recover a file that has been > > overwritten once? > > Because hard drives use magnetic imprints (I don't know the exact > term for that), even once the magnetic information has been replaced > by other information, the old one should still be present as a kind > of ghost magnetic field. Obviously, such a ghost cannot be recovered > with the tools provided with any OS. However, I guess that if a well > organized institute or electrical engineer opens your hard drive and > start analyzing the disks themselves with advanced machines, they > could "see" this ghost and extract the old information out of it. It > may sound like pure sci-fi, but I'm sure NSA has just the right tools > for the task! ;-) > > When "shred" does 10 or 20 overwrites, I guess it alternates the bit > patterns at each pass, such as to "scramble" the ghost information. > > Because one would have to actually "open" the hard drive and use > advanced machinery to extract information that was overwritten > *once*, it does not mean that doing a simple "delete" is sufficient, > since in this case it is not overwritten at all, which allows for a > simpler recovery with OS tools. > > By the way, anybody knows what are the Linux tools for that? > Something similar to DOS "undelete"? > > Mathieu. - -- Edmonton,AB,Canada User 244963 at http://counter.li.org Cooker on kernel 2.4.22-8mdk 10:45:40 up 13:18, 1 user, load average: 0.12, 0.10, 0.10 Q: What's yellow, and equivalent to the Axiom of Choice? A: Zorn's Lemon. -----BEGIN PGP SIGNATURE----- Version: GnuPG v1.2.3 (GNU/Linux) iD8DBQE/Y0wJG11CaRuZZSIRAiZBAKCueIQXLf+XwVTCJ3x49Lq8wX6xUACfZnPq Qo5ZMaVEyX5yx7ZH34u53KM= =++VY -----END PGP SIGNATURE-----
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