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Message-ID: <20040403201144.GC697@sentinelchicken.org> From: tim-security at sentinelchicken.org (Tim) Subject: erase with magnet > If you dont have such a tool or dont wont to use one, you can use dd on Linux > (Use Knoppix if you don't have it installed) > > dd if=/dev/urandom of=/dev/sda bs=1M count=1024 This will work fine against any simple forensic analysis, but if you have some very very sensitive data that say, governments, would be interested in, you need to overwrite the data many more times than this. I prefer using the free "wipe" utility, since it was written with advanced recovery techniques in mind. (To install in debian, just run `apt-get install wipe'.) The description from the man page: --- Recovery of supposedly erased data from magnetic media is easier than what many people would like to believe. A technique called Magnetic Force Microscopy (MFM) allows any moderately funded opponent to recover the last two or three layers of data written to disk; wipe repeadetly overwrites special patterns to the files to be destroyed, using the fsync() call and/or the O_SYNC bit to force disk access. In normal mode, 34 patterns are used (of which 8 are random). These patterns were recommended in an article from Peter Gutmann (pgut001@...auck- land.ac.nz) entitled "Secure Deletion of Data from Magnetic and Solid- State Memory". A quick mode allows you to use only 4 passes with random patterns, which is of course much less secure. --- Of course most people don't need this level of security, but it is good to understand the power of advanced magnetic media forensics. tim
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