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Old 07-16-2010, 04:00 PM
Ron Johnson
 
Default Securely deleting *Windows* files (was simple way to securely destroy deleted files in a file system)

On 07/15/2010 11:05 AM, H.S. wrote:


I have a couple of hard disks in a computer which is to be recycled. I
want the windows OS in it to remain functional, but I want to be sure
that I have deleted all my personal files securely (never used the OS
that much anyway and there is hardly any important info in its registry
or browser). There are a number of documents that were deleted in
Windows the usual way (Shift+del) and I just want to make them
unrecoverable.



Aren't you askig the wrong list?

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Old 07-16-2010, 04:10 PM
"H.S."
 
Default Securely deleting *Windows* files (was simple way to securely destroy deleted files in a file system)

On 10-07-16 12:00 PM, Ron Johnson wrote:


Aren't you askig the wrong list?



The filesystem is vfat, files are being deleted from within Linux using
Linux tools and the partition just happens to be a Windows installation*
but could be any generic storage device. So, no.


I presume you are implying that I ask on a Windows list. Please correct
me if I am wrong. If I am not, it would be the wrong list to ask about
using dd to delete files, unless dd is developed, or at least also being
supported, by MS.


* yes, I am aware of the OS holding some information. But if you read my
original post (and the one after that) carefully, the scope of the
security is quite limited.





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Old 07-16-2010, 05:01 PM
Ron Johnson
 
Default Securely deleting *Windows* files (was simple way to securely destroy deleted files in a file system)

On 07/16/2010 11:10 AM, H.S. wrote:

On 10-07-16 12:00 PM, Ron Johnson wrote:


Aren't you askig the wrong list?



The filesystem is vfat, files are being deleted from within Linux using
Linux tools and the partition just happens to be a Windows installation*
but could be any generic storage device. So, no.

I presume you are implying that I ask on a Windows list. Please correct
me if I am wrong. If I am not, it would be the wrong list to ask about
using dd to delete files, unless dd is developed, or at least also being
supported, by MS.



I don't think you can of= just the "empty" parts of your partition.

Attached is a Python script I use to "zero" out the free space of a
mounted partition.


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Old 07-16-2010, 05:38 PM
"H.S."
 
Default Securely deleting *Windows* files (was simple way to securely destroy deleted files in a file system)

On 16/07/10 01:01 PM, Ron Johnson wrote:


I don't think you can of= just the "empty" parts of your partition.

Attached is a Python script I use to "zero" out the free space of a
mounted partition.



Thanks for the script. You are basically writing 0xFF to the available
disk space. I used to have a C program which just did a similar thing,
writing 0x00 to a new file till the disk was full (or almost full). I
just deleted that file after I ran the program. This helped to compress
an image of the disk (using dd) quite nicely since all zeros give a
better compression ratio.


Having said that, why would dd not work the same way when I am writing
to a file using "of" on the partition in question?






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Old 07-16-2010, 06:25 PM
Ron Johnson
 
Default Securely deleting *Windows* files (was simple way to securely destroy deleted files in a file system)

On 07/16/2010 12:38 PM, H.S. wrote:

On 16/07/10 01:01 PM, Ron Johnson wrote:


I don't think you can of= just the "empty" parts of your partition.

Attached is a Python script I use to "zero" out the free space of a
mounted partition.



Thanks for the script. You are basically writing 0xFF to the available
disk space. I used to have a C program which just did a similar thing,
writing 0x00 to a new file till the disk was full (or almost full). I
just deleted that file after I ran the program. This helped to compress
an image of the disk (using dd) quite nicely since all zeros give a
better compression ratio.

Having said that, why would dd not work the same way when I am writing
to a file using "of" on the partition in question?



Yeah, I guess you could write a bash script to:
1. determine the amount of free space.
2. Divide that by some efficient block size.
3. dd if=/dev/urandom of=${VFAT}/foo.bar
obs=${BLKSIZ} count=${BLKCNT}

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Old 07-16-2010, 06:33 PM
"H.S."
 
Default Securely deleting *Windows* files (was simple way to securely destroy deleted files in a file system)

On 16/07/10 02:03 PM, Mark wrote:

On Fri, Jul 16, 2010 at 9:10 AM, H.S.<hs.samix@gmail.com> wrote:


On 10-07-16 12:00 PM, Ron Johnson wrote:



Aren't you askig the wrong list?



The filesystem is vfat, files are being deleted from within Linux using
Linux tools and the partition just happens to be a Windows installation* but
could be any generic storage device. So, no.

I presume you are implying that I ask on a Windows list. Please correct me
if I am wrong. If I am not, it would be the wrong list to ask about using dd
to delete files, unless dd is developed, or at least also being supported,
by MS.

* yes, I am aware of the OS holding some information. But if you read my
original post (and the one after that) carefully, the scope of the security
is quite limited.



Not to oversimplify the situation, but focusing on the OP's original post,
why not boot to Windows, run the Eraser program (licensed under the GNU GPL)


er ... there is a fundamental problem with that. The machine in which
the disk was being used is not currently functional due to a problem
with the power supply. So I can't really do that at this moment
(otherwise I would have done something from within Windows). Now, if
push comes to shove, and I really really have only that method to
follow, then I will have to use a power supply from a good machine to
make the older machine boot up ... when a good machine becomes available
for this.


I followed up with the dd method yesterday. Basically, I did this:
$> sudo dd if=/dev/zero of=/media/windowsdata/zeros.bin bs=4096k
count=N1; rm -f /media/windowsdata/zeros.bin
$> sudo dd if=/dev/zero of=/media/windowsxp/zeros.bin bs=4096k count=N2;
rm /media/windowsxp/zeros.bin


where how to determine N1 and N2 based on the free space available and
the type of the filesystem is left as an exercise to the reader.


I wasn't aware of the application you mentioned. Thanks to you, now I am.

Regards.



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Please reply to this list only. I read this list on its corresponding
newsgroup on gmane.org. Replies sent to my email address are just
filtered to a folder in my mailbox and get periodically deleted without
ever having been read.


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Old 07-16-2010, 06:35 PM
"H.S."
 
Default Securely deleting *Windows* files (was simple way to securely destroy deleted files in a file system)

On 16/07/10 02:25 PM, Ron Johnson wrote:


Yeah, I guess you could write a bash script to:
1. determine the amount of free space.
2. Divide that by some efficient block size.
3. dd if=/dev/urandom of=${VFAT}/foo.bar
obs=${BLKSIZ} count=${BLKCNT}



Coincidentally, that is exactly what I did (but with /dev/zero). I
posted the commands in a post just a short while ago.


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filtered to a folder in my mailbox and get periodically deleted without
ever having been read.


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