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Re: [debian-knoppix] Include wipe into Knoppix

On Mon, Nov 04, 2002 at 07:18:21PM +0100, Christian Wenke wrote:
> > Depending on which filesystem you use, erasing a file by copying random
> > data over it is not going to physically destroy the file contents on
> > your harddisk. Journaling filesystems for example create new blocks
> > when you overwrite a file, rather than overwriting existing ones. So,
> > even doing a dd if=/dev/urandom of=file_to_be_shred (which is what wipe
> > does), does not necessarily do what you expect.
> I always thought wipe does not only writes several times random data over the 
> data to be wiped out.

Great, but this does not help, because on a journaling filesystem, the
blocks that are written (or overwritten) are always new blocks. You have
no control on what blocks are physically overwritten.

> I understood this tool, as it would write some special 
> patterns in a special sequence, so that the possibility of getting old data 
> out of the effect of the magnetical remanence, is decreased more than just 
> writing random patterns. But I'm open to other explanations. :)

Again, it cannot physically overwriting the file, because it has no clue about
where the file is located on the medium.

> Another 'problem' is that if I want to overwrite a file with dd i need to say 
> dd the size of the wile. wipe deals that automatically.

No, after deleting a file, you would use dd to create a big NEW file with zeros
or random data until your entire filesystem is full. That's the only way in which
the "unused" blocks of old file versions are being physically overwritten.

-Klaus Knopper
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