scrub overwrites hard disks, files, and other devices with repeating
patterns intended to make recovering data from these devices more
difficult. Although physical destruction is unarguably the most reliable
method of destroying sensitive data, it is inconvenient and costly. For
certain classes of data, organizations may be willing to do the next
best thing which is scribble on all the bytes until retrieval would
require heroic efforts in a lab.

scrub implements several different algorithms for this:

nnsa - U.S. NNSA Policy Letter NAP-14.1-C
dod - U.S. DoD 5220.22-M
usarmy - U.S. Army AR380-19
bsi - German Center of Security in Information Technologies
gutmann - 35-pass algorithm from Peter Gutmann's 1996 paper
schneier - algorithm described in Bruce Schneier's Applied Cryptography (1996)
pfitzner7 - Roy Pfitzner's 7-random-pass method
pfitzner33 - Roy Pfitzner's 33-random-pass method