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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?"
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that the DOD standard is outdated, and that the best answer is to use 35-pass "Gutmann shredding" using passes of specific characters as suggested by Dr.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*
1. Big Magnets... For only 19.95, we'll ship you a super powerful magnet capable of realigning the entire hard disk. This device takes some time, and is best used over a couple days. Please note that while large, and heavy, this is NOT a SPEAKER MAGNET!!!! We purchase ours before they ever reach the speaker manufacturer.
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4. And finally, we would like to give you one of the finest data security measures we have to offer. The cost is 5.00 for the item, and 25.00 shipping and handling. This item utilizes new space age non-kilned ceramo-limestone material to create a heavy, yet durable and portable security measure. When the need is there, simply lift our destructo bloc about 4 feet in the air, and let it fall on your hard disk. This item guarantees hard disk breakage on the first impact, or your money back. (Shipping and handling costs not included). Item can also be thrown at incoming agents to buy time with the "DATA SENTRY". Caution: Do not drop on foot, on Glass, or on Pets. This product is in no way related to an ordinary concrete block, although you can disguise it as one if you think you are being watched!!!
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.