数据删除之Gutmann method

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Gutmann method
The Gutmann method is an algorithm for securely erasing the contents of computer hard drives, such as files. Devised by Peter Gutmann and Colin Plumb, it does so by writing a series of 35 patterns over the region to be erased.

The selection of patterns assumes that the user doesn't know the encoding mechanism used by the drive, and so includes patterns designed specifically for three different types of drives. A user who knows which type of encoding the drive uses can choose only those patterns intended for their drive. A drive with a different encoding mechanism would need different patterns. Most of the patterns in the Gutmann method were designed for older MFM/RLL encoded disks. Relatively modern drives no longer use the older encoding techniques, making many of the patterns specified by Gutmann superfluous.[

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An overwrite session consists of a lead-in of four random write patterns, followed by patterns 5-31, executed in a random order, and a lead-out of four more random patterns.

Each of patterns 5-31 was designed with a specific magnetic media encoding scheme in mind, which each pattern targets. The drive is written to for all the passes even though the table below only shows the bit patterns for the passes that are specifically targeted at each encoding scheme. The end result should obscure any data on the drive so that only the most advanced physical scanning (e.g. using a magnetic force microscope) of the drive is likely to be able to recover any data.

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Software implementations
Darik's Boot and Nuke (DBAN) (whole disk only)
Disk Utility a program provided with Mac OS X (whole disk or free space only)
Lavasoft Privacy Toolbox [1]
TrueCrypt (free space only)
Shred program of the GNU Core Utilities
srm, a Sourceforge project, also used by Mac OS X
Window Washer by Webroot Software
CCleaner