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Erase HD - one time vs 7 times?
Posted by: tlh828
Date: June 10, 2015 02:26PM
I've always thought overwriting with zeroes one time was as good as overwriting zeroes seven times. Any informed comments?
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Re: Erase HD - one time vs 7 times?
Posted by: cbelt3
Date: June 10, 2015 02:39PM
[en.wikipedia.org]

Most secure solution involves physical and magnetic destruction.
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Re: Erase HD - one time vs 7 times?
Posted by: GGD
Date: June 10, 2015 02:54PM
Quote
tlh828
I've always thought overwriting with zeroes one time was as good as overwriting zeroes seven times. Any informed comments?

You are correct, that's all it takes, at least for magnetic media.

[www.vidarholen.net]
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Re: Erase HD - one time vs 7 times?
Posted by: Racer X
Date: June 10, 2015 02:54PM
Even a 7 pass wipe can be retrieved by the government. Seriously.

Our solution at work was either hydraulic press until plates shattered, a drill, or torch it into pieces.
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Re: Erase HD - one time vs 7 times?
Posted by: vision63
Date: June 10, 2015 02:59PM
Quote
Racer X
Even a 7 pass wipe can be retrieved by the government. Seriously.

Our solution at work was either hydraulic press until plates shattered, a drill, or torch it into pieces.

Or just pour some Tung or Linseed oil on it.
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Re: Erase HD - one time vs 7 times?
Posted by: GGD
Date: June 10, 2015 03:00PM
Quote
Racer X
Even a 7 pass wipe can be retrieved by the government. Seriously.

Do you have a source for that statement? The "government" wasn't even able to recover the 18 1/2 minutes of analog audio that Rose Mary Woods did a single pass erase on.
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Re: Erase HD - one time vs 7 times?
Posted by: testcase
Date: June 10, 2015 03:00PM
The NSA already knows about your pRon........



One pass is enough.......



eye rolling smiley
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Re: Erase HD - one time vs 7 times?
Posted by: bazookaman
Date: June 10, 2015 03:28PM
Quote
tlh828
I've always thought overwriting with zeroes one time was as good as overwriting zeroes seven times. Any informed comments?

I just overwrite with sevens once.



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Re: Erase HD - one time vs 7 times?
Posted by: Racer X
Date: June 10, 2015 03:31PM
Quote
GGD
Quote
Racer X
Even a 7 pass wipe can be retrieved by the government. Seriously.

Do you have a source for that statement? The "government" wasn't even able to recover the 18 1/2 minutes of analog audio that Rose Mary Woods did a single pass erase on.

Security officer at work, at the country's 2nd largest defense contractor. Certain levels of security required destruction of drives. PERIOD.

She went to a security seminar where a seven pass wipe was recovered by a government "representative"

Residual magnetism resides on the area of the platters outside of the path of the heads. They can shift the heads by a minute amount, and read that magnetism, and the data that was last written there. Think of it this way. Take a soft lead pencil, and draw a line by pressing doswn almost hard enough to break the "lead" Now look at that line under a powerful magnifying glass. There is the graphite in the "groove" you engraved in the paper, filled with graphite powder. Now notice the graphite powder that has fretted off the pencil and is scattered on the paper on either side of the grove. Now imagine that graphite in the grove being perfectly removed. There is still graphite scattered on either side, outside the groove. THAT can be read. It represents the stray magnetic signals of 1s and 0s. Thus the data.



Edited 2 time(s). Last edit at 06/10/2015 03:38PM by Racer X.
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Re: Erase HD - one time vs 7 times?
Posted by: tlh828
Date: June 10, 2015 03:33PM
Thanks to all for your replies.
Once is enough ( for erasure, at least! ).
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Re: Erase HD - one time vs 7 times?
Posted by: Bimwad
Date: June 10, 2015 03:51PM
If the drive is of typical capacity for nowadays, the time required to zero it out will probably dissuade you anyway.
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Re: Erase HD - one time vs 7 times?
Posted by: cbelt3
Date: June 10, 2015 03:58PM
Quote
GGD
Quote
Racer X
Even a 7 pass wipe can be retrieved by the government. Seriously.

Do you have a source for that statement? The "government" wasn't even able to recover the 18 1/2 minutes of analog audio that Rose Mary Woods did a single pass erase on.

The government COULD have but did not want to. Seriously. Also technology is better now.

I still prefer Arlo Guthrie's version...

"Guthrie later wrote a follow-up recounting how he learned that Richard Nixon had owned a copy of the song, and he jokingly suggested that this explained the famous 18½ minute gap in the Watergate tapes. Guthrie re-recorded his entire debut album for his 1997 CD Alice's Restaurant: The Massacree Revisited, on the Rising Son label, which includes this expanded version"

[en.wikipedia.org]
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Re: Erase HD - one time vs 7 times?
Posted by: Paul F.
Date: June 10, 2015 04:27PM
COULD a sufficiently well funded and motivated person or organization recover a "overwrote with zeros one pass" hard drive? Yes.
Are there any casual non-governmental agencies that will take the effort, the time, and the expense? Very unlikely.

Balance the sensitivity of the data with the realistic chances that someone with the the capability will choose to try to recover that drive.



Paul F.
-----
A sword never kills anybody; it is a tool in the killer's hand. - Lucius Annaeus Seneca c. 5 BC - 65 AD
----
Good is the enemy of Excellent. Talent is not necessary for Excellence.
Persistence is necessary for Excellence. And Persistence is a Decision.

--

--

--
Eureka, CA
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Re: Erase HD - one time vs 7 times?
Posted by: Yoyodyne ArtWorks
Date: June 10, 2015 04:30PM
Quote
vision63
Quote
Racer X
Even a 7 pass wipe can be retrieved by the government. Seriously.

Our solution at work was either hydraulic press until plates shattered, a drill, or torch it into pieces.

Or just pour some Tung or Linseed oil on it.

For the win!



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Re: Erase HD - one time vs 7 times?
Posted by: GGD
Date: June 10, 2015 05:31PM
Quote
Racer X
Residual magnetism resides on the area of the platters outside of the path of the heads. They can shift the heads by a minute amount, and read that magnetism, and the data that was last written there. Think of it this way. Take a soft lead pencil, and draw a line by pressing doswn almost hard enough to break the "lead" Now look at that line under a powerful magnifying glass. There is the graphite in the "groove" you engraved in the paper, filled with graphite powder. Now notice the graphite powder that has fretted off the pencil and is scattered on the paper on either side of the grove. Now imagine that graphite in the grove being perfectly removed. There is still graphite scattered on either side, outside the groove. THAT can be read. It represents the stray magnetic signals of 1s and 0s. Thus the data.

You should read the paper that I linked above, the reason it was written was to investigate claims about methods that you are suggesting. The probability of recovering a single bit of data may be a bit better than flipping a coin, two consecutive bits lower, an entire byte, lower than a random guess, a full disk block, essentially zero, an entire drive, wishful thinking.


Can anyone find me a data recovery service that will successfully recover the contents of a hard drive that had a single pass zero applied to it, and what will they charge for that? There were no takers when someone tried this in the past.

[www.hostjury.com]
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Re: Erase HD - one time vs 7 times?
Posted by: space-time
Date: June 10, 2015 05:36PM
Quote
Racer X
Quote
GGD
Quote
Racer X
Even a 7 pass wipe can be retrieved by the government. Seriously.

Do you have a source for that statement? The "government" wasn't even able to recover the 18 1/2 minutes of analog audio that Rose Mary Woods did a single pass erase on.

Security officer at work, at the country's 2nd largest defense contractor. Certain levels of security required destruction of drives. PERIOD.

She went to a security seminar where a seven pass wipe was recovered by a government "representative"

Residual magnetism resides on the area of the platters outside of the path of the heads. They can shift the heads by a minute amount, and read that magnetism, and the data that was last written there. Think of it this way. Take a soft lead pencil, and draw a line by pressing doswn almost hard enough to break the "lead" Now look at that line under a powerful magnifying glass. There is the graphite in the "groove" you engraved in the paper, filled with graphite powder. Now notice the graphite powder that has fretted off the pencil and is scattered on the paper on either side of the grove. Now imagine that graphite in the grove being perfectly removed. There is still graphite scattered on either side, outside the groove. THAT can be read. It represents the stray magnetic signals of 1s and 0s. Thus the data.

I like you paper and pen analogy, but what if I were to write pages of zeros and pages of ones, over and over, can they still recover that? Basically that would be like filing the entire page with graphite, erasing it, repeat 7 times.

I wonder if Disk Utility can be modified to write 1 instead of 0, then I would write both, 7x and be done with it.
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Re: Erase HD - one time vs 7 times?
Posted by: tompatrick
Date: June 29, 2015 04:36AM
Quote
Racer X
Even a 7 pass wipe can be retrieved by the government. Seriously.

Our solution at work was either hydraulic press until plates shattered, a drill, or torch it into pieces.

35 Passes then (Peter Guttman algo)
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