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 Forum index » Off-Topic Area » Security
Securely erasing data from hard drives and other media
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Flash
Official Dog Handler


Joined: 04 May 2005
Posts: 11181
Location: Arizona USA

PostPosted: Wed 01 Sep 2010, 13:01    Post_subject:  Securely erasing data from hard drives and other media  

http://blogs.techrepublic.com.com/security/?p=4351&tag=nl.e040
Quote:
...There is a persistent myth to the effect that to securely delete everything from a hard drive one must overwrite it thirty-five times with random data. This myth arises from a superficial read and misunderstanding of Peter Gutmann’s 1996 paper, Secure Deletion of Data from Magnetic and Solid-State Memory. The truth of the matter, as presented in his paper, is that 35 random overwrites serves only to apply the necessary means of securely deleting data for any of several different drive technologies. A specific data storage technology only requires some lesser technique applied to ensure secure deletion.

Perhaps more interesting is the fact that, for the most modern hard drive technologies, a single complete overwrite of a drive with zeros should be sufficient. Part of the reason for this is the fact that data density on a drive is much greater than it used to be. In layman’s terms, “the bits are smaller”, which means that when rewriting, there is less room for old data to be left behind in a recoverable manner. A fair amount of redundancy of stored data occurred on older, lower density drives because the reading and writing devices were not as precise, and small deviations would leave random small areas unaffected on a single overwrite.

In a recent epilogue to his paper, Gutmann quoted himself responding to a researcher who considered doing some data testing:

Quote:
Any modern drive will most likely be a hopeless task, what with ultra-high densities and use of perpendicular recording I don’t see how MFM would even get a usable image, and then the use of EPRML will mean that even if you could magically transfer some sort of image into a file, the ability to decode that to recover the original data would be quite challenging. OTOH if you’re going to use the mid-90s technology that I talked about, low-density MFM or (1,7) RLL, you could do it with the right equipment, but why bother? Others have already done it, and even if you reproduced it, you’d just have done something with technology that hasn’t been used for ten years. This is why I’ve never updated my paper (I’ve had a number of requests), there doesn’t seem to be much more to be said about the topic.
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technosaurus


Joined: 18 May 2008
Posts: 4424

PostPosted: Wed 01 Sep 2010, 23:25    Post_subject:  

if you are doing this as a business - the time required to do the full wipe of machines to federal standards it is more cost effective to pull them all and melt them down.

randomize however many times you'd like with
dd if=/dev/urandom -of=/dev/sda
then zero out with
dd if=/dev/zero -of=/dev/sda

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Dragynn

Joined: 02 Sep 2010
Posts: 61

PostPosted: Sun 05 Sep 2010, 12:33    Post_subject:  

I have used DBAN the last few years, works great but does take around 2 hours usually to do a 100 gig drive, I usually start it then go do something else for a while.

http://www.dban.org/
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rcrsn51


Joined: 05 Sep 2006
Posts: 9370
Location: Stratford, Ontario

PostPosted: Sun 05 Sep 2010, 14:18    Post_subject:  

I find that bending over the pins of the IDE connector with a screwdriver works much faster than dban. Wink
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Dragynn

Joined: 02 Sep 2010
Posts: 61

PostPosted: Sun 05 Sep 2010, 17:41    Post_subject:  

rcrsn51 wrote:
I find that bending over the pins of the IDE connector with a screwdriver works much faster than dban. Wink


Laughing Laughing I guess I should have included some context, i'm usually hoping to re-use the aforementioned drives Very Happy
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Colonel Panic


Joined: 16 Sep 2006
Posts: 1543

PostPosted: Mon 29 Aug 2011, 07:49    Post_subject:  

DBAN's always been good enough for me. Use the "autonuke" option from the command prompt (I think you have to type F2 first), and a 20 GB drive will be thoroughly wiped in about 2 hours.

EBAN's essentially the same software, but runs over a network so you can wipe several computers at once (more cost-effective for a business which has to securely erase a lot of hard drives, as opposed to someone like me who only wipes my own).

The program you linked to looks like Windows-only.

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eternal-sunshine

Joined: 20 Feb 2011
Posts: 59

PostPosted: Mon 29 Aug 2011, 13:51    Post_subject:  

To all admins and moderators:

I posted today what I believed to be a perfectly reasonable and polite question to a post here in this thread and now see my post doesn't exist anymore nor the original post that I was responding to.

1. I would be surprised if the original post has been deleted by an admin/mod.
2. if my reply has been deleted as well then I consider that very heavy handed.
3. it would only be decent and respectful if whoever has deleted my message would have emailed me and told me why or said that in public.

I hope I am mistaken but if I am not then I fear this forum and its admin/mods have turned a very sad corner.
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AF Branden


Joined: 15 Sep 2009
Posts: 175
Location: United States, WA

PostPosted: Mon 29 Aug 2011, 15:29    Post_subject:  

Eternal, the poster you responded to was a spammer. He would have never answered your question.
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Flash
Official Dog Handler


Joined: 04 May 2005
Posts: 11181
Location: Arizona USA

PostPosted: Mon 29 Aug 2011, 16:15    Post_subject:  

Eternal-sunshine, here are the system requirements to run the software the spam post you replied to was advertising:
Quote:
System Requirements
Processor:Pentium Class
Operating System:Windows 7, Vista, Server 2003, XP, and 2000

That's why I removed the post and your reply to it. Smile
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eternal-sunshine

Joined: 20 Feb 2011
Posts: 59

PostPosted: Tue 30 Aug 2011, 05:45    Post_subject:  

Flash,
Thank you for replying and explaining why you deleted my post.
I still feel it would have been better if you had told me (PM etc).
Oh well. Smile
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AF Branden


Joined: 15 Sep 2009
Posts: 175
Location: United States, WA

PostPosted: Fri 02 Sep 2011, 14:36    Post_subject:  

If you want to be 100% sure the data is unretrievable check out the guide below:

http://www.dominopower.com/issues/issue200603/00001737002

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Dave_G


Joined: 21 Jul 2011
Posts: 459

PostPosted: Wed 14 Sep 2011, 06:30    Post_subject:  

Too complicated.
Below is the tool I use.
Works every time.

Dave.
DataRemovalTool.jpg
 Description   
 Filesize   61.05 KB
 Viewed   714 Time(s)

DataRemovalTool.jpg

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nooby

Joined: 29 Jun 2008
Posts: 10557
Location: SwedenEurope

PostPosted: Wed 14 Sep 2011, 06:41    Post_subject:  

old HDD them say one need to low level write over with 0 something several times but them say that very modern Terra byte ones are so dense that one only need to write once?

Where is the line then. 250GB is maybe too old so one need to write several times? Does it take hours most likely? Smile

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Dave_G


Joined: 21 Jul 2011
Posts: 459

PostPosted: Wed 14 Sep 2011, 06:44    Post_subject:  

nooby said:

Quote:
Does it take hours most likely?


Exactly, but with my system about 20 seconds. Laughing

Dave.
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Sylvander

Joined: 15 Dec 2008
Posts: 3555
Location: West Lothian, Scotland, UK

PostPosted: Wed 14 Sep 2011, 10:37    Post_subject:  

@Dave_G
I'm going to use your system on a faulty 750GB HDD [in a cheap/poor external enclosure] I have beside me here. Very Happy
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