Gutmann method

The Gutmann method is an algorithm that is used to totally erase the contents of a given section, such as a file on a computer drive, for security. Devised by Peter Gutmann, it does this by writing a series of 35 patterns to the drive.

Note that this selection of patterns assumes that you don't know the encoding mechanism used by the drive, and so includes patterns designed specifically for several different types of drive. If you do know the encoding mechanism used by your drive, then you can select only those patterns intended for your drive.

According to the Epilogue to the original paper, with modern (PRML) drives, writing several passes of random data is likely to be the most effective way to erase the disk.

Method

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 end result is a sufficient garbling of the data on the drive that even the most advanced physical scanning of the drive is difficult to recover any data with.

The series of patterns is as follows:

Overwrite Data
Pass No.	Data Written	Encoding Scheme Targeted
1	Random
2	Random
3	Random
4	Random
5	01010101 01010101 01010101 0x55	(1,7) RLL		MFM
6	10101010 10101010 10101010 0xAA	(1,7) RLL		MFM
7	10010010 01001001 00100100 0x92 0x49 0x24		(2,7) RLL	MFM
8	01001001 00100100 10010010 0x49 0x24 0x92		(2,7) RLL	MFM
9	00100100 10010010 01001001 0x24 0x92 0x49		(2,7) RLL	MFM
10	00000000 00000000 00000000 0x00	(1,7) RLL	(2,7) RLL
11	00010001 00010001 00010001 0x11	(1,7) RLL
12	00100010 00100010 00100010 0x22	(1,7) RLL
13	00110011 00110011 00110011 0x33	(1,7) RLL	(2,7) RLL
14	01000100 01000100 01000100 0x44	(1,7) RLL
15	01010101 01010101 01010101 0x55	(1,7) RLL		MFM
16	01100110 01100110 01100110 0x66	(1,7) RLL	(2,7) RLL
17	01110111 01110111 01110111 0x77	(1,7) RLL
18	10001000 10001000 10001000 0x88	(1,7) RLL
19	10011001 10011001 10011001 0x99	(1,7) RLL	(2,7) RLL
20	10101010 10101010 10101010 0xAA	(1,7) RLL		MFM
21	10111011 10111011 10111011 0xBB	(1,7) RLL
22	11001100 11001100 11001100 0xCC	(1,7) RLL	(2,7) RLL
23	11011101 11011101 11011101 0xDD	(1,7) RLL
24	11101110 11101110 11101110 0xEE	(1,7) RLL
25	11111111 11111111 11111111 0xFF	(1,7) RLL	(2,7) RLL
26	10010010 01001001 00100100 0x92 0x49 0x24		(2,7) RLL	MFM
27	01001001 00100100 10010010 0x49 0x24 0x92		(2,7) RLL	MFM
28	00100100 10010010 01001001 0x24 0x92 0x49		(2,7) RLL	MFM
29	01101101 10110110 11011011 0x6D 0xB6 0xDB		(2,7) RLL
30	10110110 11011011 01101101 0xB6 0xDB 0x6D		(2,7) RLL
31	11011011 01101101 10110110 0xDB 0x6D 0xB6		(2,7) RLL
32	Random
33	Random
34	Random
35	Random

See also: Eraser - Software that uses the Gutmann method

External links

• Gutmann's original paper: "Secure Deletion of Data from Magnetic and Solid-State Memory", where nearly all the information found here was taken.