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From: Stefan Patric on 29 Mar 2010 22:16
On Mon, 29 Mar 2010 15:01:52 +0800, Àî wrote:

> Thanks,
>
> But it seems that DBAN can not wipe the disk using 35 passes as file
> shredder does. How many passes can DBAN erase?

IIRC, Dban's most destructive wipe which meets the National Security
Agency's criteria for "unrecoverable" is 7 passes. It is the slowest of
the included cleansing utilities, but the most thorough.

Stef
From: mm on 30 Mar 2010 01:28
On Tue, 30 Mar 2010 02:16:23 GMT, Stefan Patric <not(a)this.address.com>
wrote:

>On Mon, 29 Mar 2010 15:01:52 +0800, �� wrote:
>
>> Thanks,
>>
>> But it seems that DBAN can not wipe the disk using 35 passes as file
>> shredder does. How many passes can DBAN erase?
>
>IIRC, Dban's most destructive wipe which meets the National Security
>Agency's criteria for "unrecoverable" is 7 passes. It is the slowest of
>the included cleansing utilities, but the most thorough.
>
>Stef

Why was more than one wipe, of all the data areas, ever necessary?

When I write a new file to a cluster, and then I read it back, it
reads what I just wrote. It doesn't include parts of what used to be
there. Because what used to be there is gone, I assume. Right?
From: Lem on 30 Mar 2010 02:22
mm wrote:
> On Tue, 30 Mar 2010 02:16:23 GMT, Stefan Patric <not(a)this.address.com>
> wrote:
>
>> On Mon, 29 Mar 2010 15:01:52 +0800, �� wrote:
>>
>>> Thanks,
>>>
>>> But it seems that DBAN can not wipe the disk using 35 passes as file
>>> shredder does. How many passes can DBAN erase?
>> IIRC, Dban's most destructive wipe which meets the National Security
>> Agency's criteria for "unrecoverable" is 7 passes. It is the slowest of
>> the included cleansing utilities, but the most thorough.
>>
>> Stef
>
> Why was more than one wipe, of all the data areas, ever necessary?
>
> When I write a new file to a cluster, and then I read it back, it
> reads what I just wrote. It doesn't include parts of what used to be
> there. Because what used to be there is gone, I assume. Right?

The theory is that with sophisticated tools, someone with physical
access to a disk can detect previously-written bit patterns. The more
times a given physical spot on the disk is overwritten, the more
difficult it is to detect the original bit value. For virtually everyone
except the more paranoid parts of the government, rewriting once, as you
describe, is sufficient.

For more information, see http://en.wikipedia.org/wiki/Data_remanence


My understanding, however, is that for really sensitive information, the
government requires physical destruction of the disk.

--
Lem

Apollo 11 - 40 years ago:
http://www.nasa.gov/mission_pages/apollo/40th/index.html
From: mm on 30 Mar 2010 16:27
On Tue, 30 Mar 2010 02:22:04 -0400, Lem <lemp40(a)unknownhost> wrote:

>mm wrote:
>> On Tue, 30 Mar 2010 02:16:23 GMT, Stefan Patric <not(a)this.address.com>
>> wrote:
>>
>>> On Mon, 29 Mar 2010 15:01:52 +0800, �� wrote:
>>>
>>>> Thanks,
>>>>
>>>> But it seems that DBAN can not wipe the disk using 35 passes as file
>>>> shredder does. How many passes can DBAN erase?
>>> IIRC, Dban's most destructive wipe which meets the National Security
>>> Agency's criteria for "unrecoverable" is 7 passes. It is the slowest of
>>> the included cleansing utilities, but the most thorough.
>>>
>>> Stef
>>
>> Why was more than one wipe, of all the data areas, ever necessary?
>>
>> When I write a new file to a cluster, and then I read it back, it
>> reads what I just wrote. It doesn't include parts of what used to be
>> there. Because what used to be there is gone, I assume. Right?
>
>The theory is that with sophisticated tools, someone with physical
>access to a disk can detect previously-written bit patterns. The more
>times a given physical spot on the disk is overwritten, the more
>difficult it is to detect the original bit value. For virtually everyone
>except the more paranoid parts of the government, rewriting once, as you
>describe, is sufficient.
>
>For more information, see http://en.wikipedia.org/wiki/Data_remanence

Thank you. I haven't read this yet but I will.

BTW, I tried to say it, but wasn't so clear. I know that when one
rewrites a file it doesn't write it to the same place the previous
copy was, and when one writes a new file, the user doesn't know what
is being overlaid. But of course in wiping a disk, it's not usually
set to wipe specific date areas but the entire disk.

Hmmm. I presume when one wipes a directory -- that's an option, isn't
it -- it will wipe everything listed in the FAT for that directory,
but what about FAT entries that have been overlaid, what about the 50
or 100 or 500 copies ofthe file that used to be in that directory?
How does it find them all? Even for a file that is still in the
directory: How does it find any copy of it except the last one, which
the FAT entry points to?

(I use FAT32. I don't remember if NTFS has a FAT, but I'm sure it has
something similar, so "Same question".

>My understanding, however, is that for really sensitive information, the
>government requires physical destruction of the disk.

Well if they're going to destroy it anyhow, can I have it?

From: Anthony Buckland on 31 Mar 2010 16:28

"mm" <NOPSAMmm2005(a)bigfoot.com> wrote in message
news:k8n4r5hk2on6dakkkcfblcpo49b6t3bo2b(a)4ax.com...
> On Tue, 30 Mar 2010 02:22:04 -0400, Lem <lemp40(a)unknownhost> wrote:
>> ...
>>My understanding, however, is that for really sensitive information, the
>>government requires physical destruction of the disk.
>
> Well if they're going to destroy it anyhow, can I have it?
>

Make an Access To Information request. When you receive the
disk, you may find that certain sensitive information areas have
been blacked out. Such as the recording surface.


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