[Linux-Discussion] Re: Linux should be able to do this... But how?
- From: "Damian Scott" <sdamian@xxxxxxxxxx>
- To: linux-discussion@xxxxxxxxxxxxx
- Date: Fri, 12 Apr 2002 17:13:28 -0700
Here's some info off IBM' DeveloperWorks public site -
Erasing the disk
You may need to store sensitive data on the hard disk without protecting
it. Perhaps your application needs to view a sensitive document that is
much too big to fit into memory all at once. Encryption might be an option
for protecting the document in some environments, but others might have
performance considerations that forbid it. The best solution is to try to
protect the file while it is in use, and delete it as quickly as possible.
But when we delete the file, does it really go away?
Usually, "deleting" a file means simply removing a file system entry that
points to a file. The file will still exist somewhere, at least until it
gets overwritten. Unfortunately, the file will also exist even after it
gets overwritten. Disk technology is such that even files that have been
overwritten can be recovered, given the right equipment and know-how. Some
people claim that if you want to securely delete a file, you should
overwrite it seven times. The first time, overwrite it with all ones, second
with all
zeroes. Then, overwrite it with an alternating pattern of ones and zeros.
Finally, overwrite the file four times with random data, such as that
generated from /dev/urandom or a similar source.
Unfortunately, this technique probably isn't sufficient. It is widely
believed that the United States government has disk recovery technology
that can thwart such a scheme. If you are really concerned about this,
then we recommend implementing Peter Gutmann's 35-pass scheme as a bare
minimum (see Resources).
Of course, anyone who gives you a maximum number of times to write over
data is misleading you. No one knows how many times will be sufficient. If
you want to take no chances at all, then you need to ensure that the bits
of interest are never written to disk with encryption, decrypting them
directly into locked memory. There is no other alternative.
I found one website that offers a program they guarantee -
http://www.ibas.ch/datenloschung/downloads/ee_product_sheets/PS-EE-10-UK.pdf
Damian Scott
> I need a way to clean a hardrive off so that the data cannot be
> recovered. There is a windows based util that the DOD uses but you have
> to put the harddrive in another machine and it wipes the disk 7 layers
> deep. Is there a linux boot disk out there that will do this.
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