US Department of Defense in the clearing and sanitizing standard DoD 5220.22-M recommends the approach “Overwrite all addressable locations with a character, its complement, then a random character and verify” (see table with comments) for clearing and sanitizing information on a writable media.
If you use FDISK, FORMAT utilities, or the standard operating system DELETE command for data removal, there is always a chance to recover the deleted files (using undelete or unformat tools) which can be used against the owner’s will.
Here are some free software that conform to this security standard, i.e. triple data overwriting for the destruction of remains of sensitive data.
Powerful and compact software that allows you to destroy all data on hard disks, SSD & USB disks completely, excluding any possibility of future recovery of deleted files and folders. It’s a hard disk drive sanitizing tool and partition eraser utility, DoD 5220.22 M compliant.
DeleteOnClick completely deletes files in one click and the data becomes unrecoverable, and also has the option to wipe free disk space. For this reason you must use the program carefully. Once a file is ‘Securely Deleted’ no one can undelete it.
- Wipes all file dates before wiping file.
- Wipes file attributes before wiping file.
- Renames files before they are deleted so that anyone trying to undelete cannot even see what the file was called.
- Quickly Wipe Free Disk Space: This will wipe all free space on the disk more quickly but is less secure than the Securely Wipe Free Disk Space option below.
- Securely Wipe Free Disk Space: This will securely wipe all free space on the disk.
- Can securely empty recycle bin.
US Department of Defense 5220.22-M Clearing and Sanitization Matrix
|Type I||a or b||a, b, or m|
|Type II||a or b||b or m|
|Type III||a or b||m|
|Bernoullis||a, b, or c||m|
|USBs(floppys)||a or b||b or m|
|Non-Removable Rigid Disk||c||a, b, d , or m|
|Removable Rigid Disk||a, b, or c||a, b, d , or m|
|Read Many, Write Many||c||m|
|Write Once, Read Many (Worm)||m, n|
|Dynamic Random Access memory (DRAM)||c or g||c, g, or m|
|Electronically Alterable PROM (EAPROM)||i||j or m|
|Electronically Erasable PROM (EEPROM)||i||h or m|
|Erasable Programmable (ROM (EPROM)||k||l, then c, or m|
|Flash EPROM (FEPROM)||i||c then i, or m|
|Programmable ROM (PROM)||c||m|
|Magnetic Bubble Memory||c||a, b, c, or m|
|Magnetic Core Memory||c||a, b, e, or m|
|Magnetic Plated Wire||c||c and f, or m|
|Magnetic Resistive Memory||c||m|
|Nonvolatile RAM (NOVRAM)||c or g||c, g, or m|
|Read Only Memory ROM||m|
|Static Random Access Memory (SRAM)||c or g||c and f, g, or m|
|Cathode Ray Tube (CRT)||g||q|
|Impact||g||p then g|
|Laser||g||o then g|
a. Degauss with a Type I degausser
b. Degauss with a Type II degausser.
c. Overwrite all addressable locations with a single character.
d. Overwrite all addressable locations with a character, its complement, then a random character and verify.
THIS METHOD IS NOT APPROVED FOR SANITIZING MEDIA THAT CONTAINS TOP SECRET INFORMATION.
e. Overwrite all addressable locations with a character, its complement, then a random character.
f. Each overwrite must reside in memory for a period longer than the classified data resided.
g. Remove all power to include battery power.
h. Overwrite all locations with a random pattern, all locations with binary zeros, all locations with binary ones.
i. Perform a full chip erase as per manufacturer’s data sheets.
j. Perform i above, then c above, a total of three times.
k. Perform an ultraviolet erase according to manufacturer’s recommendation.
l. Perform k above, but increase time by a factor of three.
m. Destroy – Disintegrate, incinerate, pulverize, shred, or melt.
n. Destruction required only if classified information is contained.
o. Run five pages of unclassified text (font test acceptable).
p. Ribbons must be destroyed. Platens must be cleaned.
q. Inspect and/or test screen surface for evidence of burned-in information. If present, the cathode ray tube must be destroyed.