DoD 5220.22-M的说明

Use this seven-pass method for tighter security. Different patterns of

bytes are written to the disk as described in the table below. Using

this method is probably even safer than using the simple method (with 6

passes).

This method is described in the National Industrial Security Program

Operating Manual (NISPOM a.k.a. DoD 5220.22-M) of the US Department of

Defense (January 1995; chapter 8, section 3, 8-306. Maintenance).

The free disk space is overwritten seven times:

Pass Data

1 A random character, n = [0, 255]

2 A random character, n

3 Complement of previous character, ~n

4 A random character, n

5 A random character, n

6 Complement of previous character, ~n

7 A random character, n

However, if you want to be absolutely sure of your data security, use the Gutmann method, below</