On Tue, Dec 22, 1998 at 10:36:19AM +0100, Steffen Grunewald wrote:
> Why urandom ? The safest way to destroy all information on disk should
> be to reverse _all_ magnetic particles (flip and flip back)=20
> |>=20
> |> AFAIK DoD military grade wiping is zero->random->zero->random->zero.
>=20
> A better scheme would be 10101010 - 01010101 - 11111111 - 00000000
>=20
> BUT:
>=20
> if I write a bit pattern to the disk - how is it stored ?
> Remember, CD data are re-encoded to avoid long 1 or 0 patterns.
> I'd guess, with fuzzy bit stuffing nowadays harddisk use similar
> techniques... so perhaps a "all ones / all zeroes" pattern is
> re-encoded to something that is near ...01010101010...
>=20
The kernel, filesystem, and wiper code all have to support this
properly. Forgive my ignorance on the below; I've never really looked
into the lower levels of FS code.
Correct me if I'm wrong, but if I write a file, then shrink it,=20
ext2 doesn't know where the space went, so a secure deletion utility=20
can't overwrite it. If we're talking about files written by text=20
editors, utilities like patch, and other such things, the application=20
doing the shrinking doesn't know to wipe the data before shrinking.=20
Is this a case for the (not working, AFAIK) "s" ext2fs file attribute?
It could probably be modified to overwrite the file with whatever
patterns are deemed best.=20
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