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New Tech In Data Retrieval
Johnath writes: "Story over at Science News about magnetoresistive microscopy, which allows very high-res inspection of magnetic media. The article is touting it primarily as a forensic tool, and gets me thinking -- how many passes of write-over-with-random-data are now required to securely delete a file?"
Still, the equipment necessary to recover a 7 times read/write-over pass is probably out of the price range of all but the most well-funded groups; I wouldn't worry too much about it, especially if you use an encrypted file system and encrypted swap files.
Free music from Jack Merlot.
Briefly, the main problems are the "ghost" of the old data, track misalignment leaving part of the old data on the side of a track, and bad sectors which are marked off by the drive electronics. There are also issues with drives that promise to write the data to the store immeditately, but in fact just cache it.
The only thing you can do is overwrite with random data several times in the hope that this will be enough.
Paul.
You are lost in a twisty maze of little standards, all different.
*Link to GPL'd Source Code Below*!
l .html
The DOD standard you and others mention specifies a specific set of patterns to be used for each pass, in order to maximize the chances of making the data unrecoverable. It's specified in DOD 5220.22-M and generally referred to as "DOD standard 7-pass extended character rotation wiping," which is quite a mouthful.
Sami Tolvanen has done some excellent research into the area, however, and at
http://www.tolvanen.com/eraser/
he goes into specifics, including scientific papers and providing links to the actual text of the DOD standard. He also provides a Windows binary for download and *GPL'd SOURCE CODE*, for a program he wrote called Eraser which is probably the best file shredding util out there. He concludes, based in part on a scientific paper at
http://www.cs.auckland.ac.nz/~pgut001/secure_de
that the DOD standard is outdated, and that the best answer is to use 35-pass "Gutmann shredding" using passes of specific characters as suggested by Dr. Gutmann in his paper linked above.
Maybe some people should start porting Eraser to Linux, nudge-nudge wink-wink hint-hint.
"The more corrupt the state, the more numerous the laws."--Tacitus, *The Annals*
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krystal_blade
It will be easy to motivate our fellow man; there is hardly anything people treasure more than not being annihilated.
Colin Plumb's shred(1) is part of GNU fileutils 4.0, standard install on Red Hat 6.2. From the info page:
"This uses many overwrite passes, with the data patterns chosen to maximize the damage they do to the old data. While this will work on floppies, the patterns are designed for best effect on hard drives. For more details, see the source code and Peter Gutmann's paper `Secure Deletion of Data from Magnetic and Solid-State Memory', from the
proceedings of the Sixth USENIX Security Symposium (San Jose, California, 22-25 July, 1996)."
Ask a silly person, get a silly answer.
1) -Triggering of a super strong electro-magnet, followed by,
2) -An instantaneous release of acid that would eat away at the surface of the disk.
These ideas may seem stupid to most, but you must realize that by opening a harddrive, you are ruining it anyway. I got this idea from the Guinness Tall Boy cans which have a Nitrogen Booster that gets released as soon as you open the can. The drives would have to be manufactured in such a way that these mechanisms could not be interjected before opening the case. This kind of hardware would not be targeted to the average consumer, but to those who may feel a little paranoid about the MAN getting a hold of their data.
http://www.nist.gov/public_ affairs/releases/g00-108.htm
I don't think this press release is referenced at the Science News article.
> I'm not a data recovery expert, but wouldn't a random sequence of bits written between
> each step of writing the specified sequential pattern of bits make it harder to
> establish physical patterns during data recovery?
The point of using specified patterns when wiping is so that those patterns will have the combined effect of completely obliterating the magnetic signature of any stored data. That's why certain patterns are mathematically thought to have a much more useful effect in the secure deletion of files than just using random data.
Think about it this way; the following parallel isn't accurate as to the exact process, but should illustrate the same methodology: You have a few lines of text written on a sheet of paper, and you wish to render them unreadable even to very close examination. (Obviously you'd burn the paper, but for the sake of example assume we have to keep the paper.) Now, what would be most effective in destroying your writing, randomly scribbling over each character, or carefully writing successive patterns of other letters over the existing ones in order to methodically obliterate them? A simplistic analogy, but that's the easiest way to grok it. I doubt 100 passes of random data could be as effective as 35-pass Guttmann wiping.
"The more corrupt the state, the more numerous the laws."--Tacitus, *The Annals*
- da Lawn
't used to be LawnMOWER, really...
If you can't count on your data being dead even after you performed a multi-pass wipe of the hard drive and then burned it, then where do you seek protection?
Obviously, encryption.
Big brother is watching, if you want to keep anything secret you better use something that will at least be hard for "them" to penetrate. Encryption is the only known last defense.
Hmmm, let's see if I can get Echelon to take notice of this post. Nuclear weapons grade plutonium uranium kryptonite terrorism attack make the infidels pay bomb blood killing death www.terrorists.org DEATH TO THE UNBELIEVERS! allah'u akbar muhammad purple monkey dishwasher.
My dad was working for Controll Data Corporation back in the '70s, which was then a big comptuer company. (Cray designed their systems before starting his own company).
They had drum drives. Like a normal harddrive, but instead of a platter it was a drum (like a big tin can). The department of defense bought on of these units, which turned out to be defective. After a few days of operation it broke, and deformed the drum. There was now no machine that could read it. They DOD sent it back to the factory for replacement - with two armed gaurds. Those gaurds were with the machine at all times until technitions opened the case. Then they took rags, rubed the magnetic coating off the drum, and burned the rags.
The military actually uses these things. One of the neater James Bond devices I've seen is what appears (at first glance) to be two thick hanging file folders. One at the front of the drawer, one at the back. Then you notice the wires attached to them. They're shaped explosive charges, designed to completely destroy the contents of a file cabinate or safe quicky. For use in the event of "imminent compromise" of security by enemy forces.
dragonhawk@iname.microsoft.com
I do not like Microsoft. Remove them from my email address.