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Old 07-15-2010, 05:38 PM
"Perry E. Metzger"
 
Default simple way to securely destroy deleted files in a file system

On Thu, 15 Jul 2010 12:05:33 -0400 "H.S." <hs.samix@gmail.com> 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.
>
> Its first and second partitions (sdc1 and sdc2) are vfat. I was
> thinking of mounting these on /mnt/scd1 (and scd2) and then doing:
> # dd if=/dev/zero > /mnt/sdc1/zeros.bin; rm -f /mnt/sdc1/zeros.bin
>
> and the same for scd2. The idea is fill the partition with new data
> thus overwriting any deleted files' data that is lying around.
> Would that be adequate? The objective is just to prevent a casual
> recovery, reading and copying of the data by a future user, so I
> don't need multiple over-writes.

I suggest dd'ing /dev/zero over the raw disk partition instead. That
will zero out every single block of the file system. You can probably
just do

dd if=/dev/zero of=/dev/scd bs=1M

or some moral equivalent.

--
Perry E. Metzger perry@piermont.com


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Old 07-15-2010, 05:55 PM
"H.S."
 
Default simple way to securely destroy deleted files in a file system

On 15/07/10 01:38 PM, Perry E. Metzger wrote:
> On Thu, 15 Jul 2010 12:05:33 -0400 "H.S." <hs.samix@gmail.com> wrote:

>> Its first and second partitions (sdc1 and sdc2) are vfat. I was
>> thinking of mounting these on /mnt/scd1 (and scd2) and then doing:
>> # dd if=/dev/zero > /mnt/sdc1/zeros.bin; rm -f /mnt/sdc1/zeros.bin
>>
>> and the same for scd2. The idea is fill the partition with new data
>> thus overwriting any deleted files' data that is lying around.
>> Would that be adequate? The objective is just to prevent a casual
>> recovery, reading and copying of the data by a future user, so I
>> don't need multiple over-writes.
>
> I suggest dd'ing /dev/zero over the raw disk partition instead. That
> will zero out every single block of the file system. You can probably
> just do
>
> dd if=/dev/zero of=/dev/scd bs=1M

Yes, but that would wipe out everything, the OS as well.

I was looking for just making the already deleted files unrecoverable by
a casual user. In other words, since a deleted file frees the space on
disk, by filling up the disk with all zeros and then deleting that zeros
file would be overwriting the earlier deleted files with zero. Am I
correct in this?





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Old 07-15-2010, 06:00 PM
"H.S."
 
Default simple way to securely destroy deleted files in a file system

On 15/07/10 12:31 PM, Wolodja Wentland wrote:
>>
>> Its first and second partitions (sdc1 and sdc2) are vfat. I was thinking
>> of mounting these on /mnt/scd1 (and scd2) and then doing:
>> # dd if=/dev/zero > /mnt/sdc1/zeros.bin; rm -f /mnt/sdc1/zeros.bin
>>
>> and the same for scd2. The idea is fill the partition with new data thus
>> overwriting any deleted files' data that is lying around. Would that be
>> adequate? The objective is just to prevent a casual recovery, reading
>> and copying of the data by a future user, so I don't need multiple
>> over-writes.
>
> Take a look at "secure-delete" which contains "sfill" which can be used
> to fill the available free space on a hd with random (and specifically
> crafted) data to ensure that data recovery is impossible. I am not sure
> if it works with vfat though :-

I am looking at its man page, which starts with

"sfill is designed to delete data which lies on available
diskspace on mediums in a secure manner which can not be recovered by
thiefs, law enforcement or other threats. The wipe algorythm is based
on the paper "Secure Deletion of Data from Magnetic and Solid-State
Memory" presented at the 6th Usenix Security Symposium by Peter Gutmann,
one of the leading civilian cryptographers."

Talk about overkill!

Sfill has some options which will make it easier and faster (by not
doing it in the most robust and time expensive fashion) to delete/free
disk space. I just have to verify how it work and I don't inadvertently
delete files which I am not supposed to.

Thanks.




> good luck
>
> Wolodja


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


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Old 07-15-2010, 06:13 PM
thib
 
Default simple way to securely destroy deleted files in a file system

Take a look at shred (coreutils), wipe and secure-delete.

-t


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Old 07-15-2010, 06:24 PM
Mark
 
Default simple way to securely destroy deleted files in a file system

On Thu, Jul 15, 2010 at 9:05 AM, H.S. <hs.samix@gmail.com> 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.



Its first and second partitions (sdc1 and sdc2) are vfat. I was thinking

of mounting these on /mnt/scd1 (and scd2) and then doing:

# dd if=/dev/zero > /mnt/sdc1/zeros.bin; rm -f /mnt/sdc1/zeros.bin



and the same for scd2. The idea is fill the partition with new data thus

overwriting any deleted files' data that is lying around. Would that be

adequate? The objective is just to prevent a casual recovery, reading

and copying of the data by a future user, so I don't need multiple

over-writes.
This makes sense to me. * As you said dd'ing the partition will blank everything including Windows.* Alternatively, if you know of a directory you want everything inside shredded with zeros, you can use:


# find -type f -execdir shred -vfzu -n 0 '{}' ;
# rm -rf *

HTH.

Mark
 

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