Eric Townsend writes:
The US Gov policy for the disposal of any media that has been used to store classified data is: wipe -- demagnatize with a *massive* demag unit grind -- toss in a thing that'd make ground chuck out of godzilla incenerate -- at some amazingly high temperature. The media is treated as if it had classified data until after step #3.
In addition to degaussing, crushing, and incenerating classified disks, the US Government has approved a number of software systems that overwrite the media with ones and zeros. Different agencies have different rules and defense contractors have to obey the rules of the agency that they are servicing. The NSA and DOE require four passes over the data with the patterns 0x00, 0x55, 0xAA, and 0x41 (these are hex byte values). The last value is the Ascii letter 'A', which is then verified by spot checking. This pattern flips each bit at least once after setting all bits to zero. With a scanning electron microscope it is possible to pick up fringe regions of the magnetic domains and reconstruct the last dozen or so values for a particular domain. This result means that if a disk has really sensitive information, and it is leaving the secure facility (i.e., not just being re-used for another project, or being transfered to another secure location), then the four-pass overwrite program must be run at least three times. There are also low-level considerations. The main one is that the disk head must be wiggled back and forth as it moves along the disk to vary the alignment between the head and the track to maximize the erasure of outlying magetic domains. If the head is simply stepped from track to track, all tracks will miss the same outlying domains because the head stepping error rate (e.g., 2% off true alignment in the inbound direction) tends to remain constant as the head moves inward. Another low-level consideration is to be sure to erase all the data surfaces including sector headers, bad blocks, alternate cylinders, disk label regions, and sectors reserved for holding redundant copies of the disk geometry information or the disk controller microcode. All this requires going below the operating system to directly issue SCSI or IDE disk commands. LAT sells the only overwrite program that has been approved for Unix platforms. --Bob ---------------------------------------------------------------------- Director of Development Our mission is to provide Los Altos Technologies, Inc. the best solutions to our Voice: 415/988-4848 customers' key computer Fax: 415/988-4860 security problems while email: baldwin@lat.com increasing their productivity. ----------------------------------------------------------------------