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SteveDeFacto

Files can always be recovered no matter what you do...

34 posts in this topic

[quote name='cowsarenotevil' timestamp='1316825319' post='4865362']
Also, the "just because there haven't been any published cases of data being recovered doesn't mean it's not happening! The government just keeps it secret" argument isn't compelling to me.
[/quote]
I never said that. I don't know if anyone does it. I don't know if anyone is going to be able to do it in 20 years on a current day harddisk. But asserting with certainty that it is 'impossible' is dangerous and a bit naive.

Fact is, the physical processes behind magnetic storage are not controllable down to an atomic level in a device like a harddisk. Can you [i]guarantee[/i] that your HDD does not leave [i]any trace[/i] of the original data when you overwrote it with zeros ? Not the slightest area, even if its only a few molecules wide ? Can you guarantee that it still won't even after years of mechanical wear and tear, reduced servo precision or reduced magnetic writing energy due to slowly failing heads ? Would you bet your life on it ? I certainly wouldn't. That's why there are much stricter procedures for data that is so sensitive that people would go a very long way to get a hold of it and that could have significant consequences if compromised (think nuclear weapons construction data and similar). Comparing this to psychics is a bit ridiculous, to be honest.

Of course all that doesn't apply to a normal user or company. For all common use scenarios, a simple overwrite is perfectly fine.
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[quote name='Yann L' timestamp='1316828315' post='4865370']
Would you bet your life on it ? I certainly wouldn't.[/quote]

Would you bet your life on the non-existence of psychics? I certainly wouldn't. I'd bet quite a bit of money on both, though. I also think it's highly unlikely that 50 years from now the government will reveal that they've been recovering wiped data all along and keeping it secret, as you seem to imply (or even that they'll be able to do it in the next 50 years). That said, I agree in that in most cases information on a macroscopic scale is [i]theoretically[/i] recoverable.
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[quote name='cowsarenotevil' timestamp='1316825319' post='4865362']
there [i]are[/i] cases of data being recovered from a disk that's shredded:[/quote]
[Citation needed]

And they recover valid non-erased data. That is, in some cases of physical damage, possible. But it's a completely different game from reconstructing deleted data.

[quote]you can just scan the pieces with an electron microscope, the reconstruct them with a computer (the data tracks follow a predictable curve so it's not at all hard to figure out where even a small piece belongs).[/quote]
[Citation needed]

Because... things just don't work that way.


[quote]It is extremely unlikely that there is [i]nothing[/i] there.[/quote]
Of course it is. In the same way the leaf I stepped on is now deformed.

But can this be used to reconstruct the data? I say no. Not deleted data.

[quote]...governments...NSA...DoD...[/quote]
Again, let's be real here.

Governments and these agencies can't even find perfectly indexed data. They are bureaucrats. They contain politicians, senators, people with connections, friends of family. When work needs to be done, they outsource it to government contractors. To avoid corruption, these contractors need to file a lot of paperwork to prove that their bribes are legit. So they contain a lot of paper pushers. So they again delegate work to Joe's Computer Recovery Shop. Who does the work under lockdown.

Really. There are no secret labs in Pentagon, there is no elevator going down 5 miles in NSA headquarters. That's Hollywood.

There is another reason, a purely engineering one. Managers like to talk. But when dealing with such delicate and one-off work, you cannot risk. You cannot be agile and learn from mistakes, it needs to work for the first time.

So to perform such recovery, there is only a handful of shops in the world that employ people who have been doing nothing but for past 20 years. Not government work, but recovering disk of a CEO who sat on it. Or folded a floppy in half. Or spilled coffee over it. And since those mysterious agencies aren't running such shops in their secret labs under volcano, they are commercial ventures, which might have, before budget cuts, even have some standing orders with governments. But little more.

And the devices, work, etc. they do, has been developed at public universities, is publishes as thesis, there are patent applications, presentations were had on conferences.


Like I said, it's romantic, but things just don't work like that in real world. In real world, such discovery would get stonewalled because the junior researcher wouldn't properly attribute their mentoring professor who would then hold a grudge and discredit the guy and have them kicked off the faculty while destroying their paper out of jealousy.
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[quote name='Antheus' timestamp='1316873019' post='4865471']
Again, let's be real here.
[/quote]
Good idea. First step would be to get off this "OMG you said gov't, teh CONSPIRACY !!1" trip, shall we ? Governments are obvious candidates for data forensics. If that makes you feel better, replace every instance of "government" in my posts above with "bored student with access to a big lab and too much time on his hands who wants to use university resources to reconstruct his accidentally deleted porn collection".

Second, let's get back to the technical side. So on one hand we have a harddisk. A very low cost mass produced device that is subject to large environmental influences, manufacturing tolerances, considerable wear and tear, mechanical shock, possibly bad power supply, interferences, and much more. A device that is just as precise as it needs to keep data integrity in a more or less acceptable range. Do you operate your harddisk in a temperature, humidity and pressure controlled HF shielded cleanroom ? Does it come certified by the manufacturer that it will write down to molecular precision and that every write will induce exactly the same field strength ? Do you have it recalibrated every month ? No ? Well, your HD is going to spill its magnetic signal all around the intended write track. Magnetization is a stochastic operation. You will never get 100% repeatability unless you are using feedback on almost atomic level or subject the magnetic material to a very high power magnetic field (ie. degaussing). And the latter isn't even 100.00% certain either.

On the other hand we have devices that are capable of measuring this magnetization down to the molecular scale [url="http://nano.tm.agilent.com/"]readily available[/url] on the market.

So your conclusion from this is that reading the data is [i]categorically impossible[/i]. Proof by [i]"because no one has yet published a paper on it"[/i]. Right...

Oh well. Thankfully the organizations (evil conspiring big corporations and governments for example) with information that could actually impact our lives do not subscribe to your point of view :rolleyes:
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[quote name='Antheus' timestamp='1316873019' post='4865471']
And they recover valid non-erased data. That is, in some cases of physical damage, possible. But it's a completely different game from reconstructing deleted data.
[/quote]

Yes, that's [i]exactly[/i] my point. If you overwrite your data, even once, then physically destroying your disk "just to be more sure" is a waste of time, because it's a lot easier to recover a hard drive that's been physically damaged than to recover one that's been overwritten.

[quote][quote]you can just scan the pieces with an electron microscope, the reconstruct them with a computer (the data tracks follow a predictable curve so it's not at all hard to figure out where even a small piece belongs).[/quote]
[Citation needed][/quote]

Here's a [url="http://computer-forensics.sans.org/blog/2009/01/28/spin-stand-microscopy-of-hard-disk-data/"]random link I found[/url]. If you're wondering, I originally heard the story of recovering a shredded (physically) hard drive from a [url="http://www.cs.cmu.edu/%7Egkesden/"]Greg Kesden[/url] many years ago. He mentioned specific instances in which this has been done (for demonstration purposes); I can't recall them.
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[quote name='Yann L' timestamp='1316886016' post='4865520']
So your conclusion from this is that reading the data is [i]categorically impossible[/i].[/quote]

No, my conclusion is that is hasn't been done.

[quote]Proof by [i]"because no one has yet published a paper on it"[/i]. Right...[/quote]

It has to do with that thing called scientific method. But agreed, when it comes to IT, that is indeed a joke.

Fortunately, some people actually try to move beyond Feng Shui, voodoo and witchcraft and approach this in neutral manner - by [url="http://www.cs.auckland.ac.nz/%7Epgut001/pubs/secure_del.html"]publishing stuff[/url]. Even then, despite being sound, there is dire lack of evidence of any kind that such method ever successfully recovered erased data. And that is dealing with 30+ year old technology.

[url="http://en.wikipedia.org/wiki/Data_remanence#Feasibility_of_recovering_overwritten_data"]More papers[/url] (I'll trust that wiki summary is correct). "On the other hand, according to the 2006 [url="http://en.wikipedia.org/wiki/NIST"]NIST[/url] Special Publication 800-88 (p. 7): "Studies have shown that most of today’s media can be effectively cleared by one overwrite" and "for ATA disk drives manufactured after 2001 (over 15 GB) the terms clearing and purging have converged."[sup][url="http://en.wikipedia.org/wiki/Data_remanence#cite_note-SP800-88-0"][1][/url][/sup] An analysis by Wright et al. of recovery techniques, including magnetic force microscopy, also concludes that a single wipe is all that is required for modern drives. They point out that the long time required for multiple wipes "has created a situation where many organisations ignore the issue all together – resulting in data leaks and loss. "[url="http://en.wikipedia.org/wiki/Data_remanence#cite_note-wright-4"]"[/url]

The NIST report should be taken very seriously and it goes along with my original suggestion. At massive scale, wiping drives may be time consuming. And since companies hosting such data do not want to spend money on tasks like that, industrial shredder is by far most cost effective method. Grind 50 disks together and the data is, for all practical purposes, non-recoverable. Because alternative today is that these drives are, without any data destruction, physical or software, delivered in labeled bags to dump. To recover, one doesn't need effort, just an IDE or SATA connector.


Finally, on publishing. Researchers these days are in dire need of justifying their own existence. They fight tooth and nail for grants in oversaturated fields, they are scrambling to reword their "images in social networks" paper for the 12th time so they meet their quota.

And here is something that has never been done or apparently is done regularly or at least has been done - and nobody writes a single paper? The field could be milked for a lifetime. It's enough to fuel several tenures over. And nothing? Not even a single tiny footnote? Not even for a 30 year old MFM drive? A floppy? A patent?

----
Or maybe we should count each other's badges. I have 18, including knitting. So if anyone has more, then you are right and I'm wrong.

After all, it works for the OP's teacher, should work here as well.

[quote]bored student with access to a big lab and too much time on his hands who wants to use university resources to reconstruct his accidentally deleted porn collection[/quote]

If you are a student, please do this. You have a career made. And the foundation for an incredibly reliable recession-proof business.
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[quote name='Antheus' timestamp='1316890855' post='4865539']
[quote name='Yann L' timestamp='1316886016' post='4865520']
So your conclusion from this is that reading the data is [i]categorically impossible[/i].[/quote]

No, my conclusion is that is hasn't been done.
[/quote]
So you know about every possible attempt by every possible individual with access to the required technology anywhere in the world, who may for whatever possible reason not have published a paper on it. Okay. That's quite some impressive knowledge you have there. I personally prefer to be a bit more cautious (even though my own data is nowhere near that sensitive, so a simple overwrite is indeed all I need).

This discussion isn't leading anywhere and incidentally I have an internal research report to read over for monday and I haven't even started. A paper that will never be published. So that means the experimental technology it describes probably doesn't even exist and I can safely throw it away. Phew, the weekend is saved !

Oh well, enough sarcasm. Peace :)
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[quote name='Yann L' timestamp='1316892375' post='4865549']
So you know about every possible attempt by every possible individual with access to the required technology anywhere in the world, who may for whatever possible reason not have published a paper on it. Okay. That's quite some impressive knowledge you have there. I personally prefer to be a bit more cautious (even though my own data is nowhere near that sensitive, so a simple overwrite is indeed all I need).[/quote]

Since you're busy I won't hold it against you if you don't reply, but again, I don't see how this argument doesn't apply equally as well to "psychics." So how, exactly, is the comparison "ridiculous"? Surely there are [i]more[/i] attempts by individuals to use psychic powers than there are to recover overwritten data, and people who are successful have just as much incentive to keep their abilities secret.

[quote]Such cases would most likely be classified or involve illegal activities (such as high profile industrial espionage). Wait 50 years and some may fall under the FOIA.[/quote]

If I said this about governments secretly using psychics to catch criminals, would you take me seriously? Of course I can't rule out the [i]possibility [/i](either of psychics [i]or[/i] data recovery), but it really seems hardly worth considering when there's [i]no evidence at all anywhere[/i].
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I would agree that you can erase a file beyond recovery. I would simply have a program write over the data a few times with actual data of the same file type randomly found on the internet. Then set all of the bits to 0. There would be no way of knowing if the recovered data came from the random data pulled from the internet or the original file. Those are my two bits.
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