History

In February 1995, the first version was issued. This version specified a procedure to overwrite data on a hard disk drive (HDD) with zero and one patterns three times. This became known as the DoD 5220.22-M sanitization method.

In January 2001, the Department of Defense designated the DoD 5220.22-M ECE sanitization method as an extension of DoD 5220.22-M. This method required seven overwrite passes.

In February 2006, the latest version of DoD 5220.22-M was issued. In this version, the overwrite pattern was no longer specified as a data erasure method for HDDs. Instead, other sanitization methods such as erasure, degaussing, and physical destruction were recommended.

In December 2014, DoD 5220.22-M was revised. In this version, the sanitization method guidelines were updated to accommodate new technologies such as flash-based storage and mobile devices.

In May 2019, the Department of Defense stopped referring to DoD 5220.22-M and instead complied with the media sanitization guidelines of the National Institute of Standards and Technology (NIST SP 800-88).

Write 0

• dd is a command to copy data¹.
• if=/dev/zero specifies /dev/zero as the input file. /dev/zero is a special file that outputs zeros indefinitely.
• of=/dev/sdb specifies /dev/sdb as the output file. /dev/sdb is a device file for hard disks, USB memory, etc.¹.
• bs=4096 specifies 4096 bytes as the block size. The block size is the unit of data to read and write at a time.

This command copies zeros from /dev/zero to /dev/sdb in 4096-byte increments, overwriting and erasing the data on /dev/sdb.

Write 1

• tr is a command that converts characters.
• '0', '377' convert the input characters from \0 (0 in octal) to \377 (255 in octal). This converts 0 bits to 1 bits.
  • ((3 x 8) + 7) x 8 + 7 = 255
• < /dev/zero specifies /dev/zero as the standard input source.
• > /dev/sdb specifies /dev/sdb as the standard output destination.

This command reads 0 from /dev/zero, converts it to 1 in tr, and converts it to 1 in /dev/sdb By continuing to write , the data in /dev/sdb will be overwritten and erased.

Write random numbers

Reads random data from the device /dev/urandom and writes it to /dev/sdb.

Using /dev/urandom takes longer than using /dev/zero. This is simply because generating random numbers takes time. /dev/urandom generates random numbers from environmental noise (device related conditions such as mouse, keyboard, etc.).