Destroying Data

Jim Thompson jim at
Mon Dec 21 10:08:34 PST 1992

> 	Consider also the technique used in the Norton Utilities
> 	program "Diskwipe" which takes a /g switch which "Follows
> 	certain government rules for wiping". I can't find the manual
> 	but I think it specifies how many repetitions are used and
> 	different values to write in each. 

SunOS 4.X 'format/analyze/purge', (which was done at the request
of SunFed, for some Fed contract) uses 4 repetitions with patterns:

	0xaaaaaaaa	(10101010)
	0x55555555      (01010101)
	0xaaaaaaaa      (10101010)
	0xaaaaaaaa      (10101010)

Followed by a final pass with:

	0x40404040	(10000000)

Consider this secure if you want.  :-)  For Unix variants, one
might consider a 'patch' to libc that scribbled on the file passed
to the 'unlink()' system call before actually performing the syscall.

This will, of course, break Unix semantics because there is no way
to tell from userland that no other process is holding the file open,
so you'll scribble on the file prematurely.  I guess itrunc() is what
really need changing.


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