declassifying media there are many urban legends maybe this ought to be in the crypt faq about what is actually sufficient to clear or declassify magnetic media when used for classified data here is some information from the horse s mouth regarding the sufficient overwriting of media clearing meant to be retained within the controlled environment or declassifying the material to be reused outside the controlled environment from national telecommunications and information systems security ntiss advisory memorandum on office automation security guidelines ntissam compusec clearing of magnetic media certain types of removable media e g magnetic tape floppy disk cassettes and magnetic cards may be cleared by overwriting the entire media one time with any one character floppy disks may be cleared by applying a vendor s formatting program that overwrites each location with a given character fixed media e g winchester disks should be cleared by overwriting at least one time with any one character one way to do this is by applying a vendor supplied formatting program that overwrites each location on the disk with a given character if it can be shown that this program actually works as advertised the user should beware some programs that purport to overwrite all locations do not actually do this cleared media may be resides within the controlled facility or released for destruction however they should be marked and controlled at the level of the most restrictive sensitivity of information ever recorded declassification of magnetic media certain types of removable media can be declassified using a degaussing device that has been approved for declassifying media of that type a list of approved devices is maintained by the nsa if a fixed medium for example a hard or winchester disk is operative an approved method of declassifying the disk pack is to employ an overwrite procedure which must overwrite all addressable locations at least three times by writing any character then its complement e g binary ones and binary zeros alternatively when fixed media become inoperative it is impossible to declassify the media by the overwrite method in this case there are two alternate procedures that may be used disassemble the disk pack and degauss each platter with the appropriate approved degaussing equipment and courier the inoperative media to the vendor s facility have the magnetic media e g disk platter removed in sight of the courier and returned to the courier for destruction at the secure site the vendor can then install new platters and repair any other problems with the disk unit destruction of magnetic media see dod computer security center department of defense magnetic remanence security guideline csc std for official use only this and many other interesting documents many that are more informative than probably intended on computer security procedures can be obtained free from executive secretary national telecommunications and informations systems security committee national security agency fort george g meade md write them it s fun to be on the nsa s mailing list grady netcom com ef e ad d d c f fc ac f d f e f
