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A New Technique to Quickly Erase Hard Drives
Posted by
CowboyNeal
on Sat Jun 17, 2006 10:41 AM
from the clean-and-clear dept.
from the clean-and-clear dept.
RockDoctor writes "Stories about 'wiped' hard drives appearing on eBay (and other channels) and being stuffed with personably-identifiable data are legion; rarer are spy planes having to land on enemy territory, but it happened in 2001 to a US spy plane over an un-declared enemy (China, and that's a topic in itself). Dark Reading reports the development of a technique to securely wipe a hard drive in seconds, and which is safe for flying. (The safe for flying criterion rules out things like fun with packing the drives in thermite. Also thermiting the drives may not erase the platters to the standard required, which is moderately interesting itself."
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Ask Slashdot: How to Say Goodbye to Old Hard Drives? 337 comments
An anonymous reader writes "I'm wondering if anyone else out there has a stack of old hard drives sitting around and doesn't know what to do with them. I always remove the hard drives of my parents' and friends' computers before they recycle them or get a new computer, so now I've got a whole bunch sitting around. One, I'd like to dispose of them and know that whatever data was there is gone, but before that, I'd like to hook them up, one by one, and scan them to make sure there's nothing vital there worth saving. Some are years old and may be totally dead for all I know, but is there a good system for hooking up a hard drive as an additional device, perhaps via USB? And what's a pretty good way to ensure that someone else won't pull them out later on and find usable data?" Well to start with you could always use your hard drives to make electricity or create a decorative wind chime. There are also many different options to ensure that your data doesn't fall into the hands of the enemy. What other suggestions can folks come up with?
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Computer systems and their hard drives (Score:3, Funny)
How curious that the anti-bot please-type-in-this-word word is kilobyte for this post.
Re:Computer systems and their hard drives (Score:5, Funny)
You never have to worry about arcane details such as hard drives, magnetic field strength etc etc.
Parent
Joe does it (Score:5, Interesting)
Now if it's just some random joe with an undelete program he got for $19.99 at the local shop then a single pass is often enough, more sophisticated software only tools might get past a few, but with hardware equipment (probably not used often below the fbi/pro forensics places) you might want to do something a bit more secure.
With good knowledge of how the data is actually stored on the disk you can figure out patterns that tend to degausse the bits being wiped and help eleminate the residual images left by the micro imperfection in head positioning (which are shrinking to almost nothing these days) and simular effects a trully sophisticated data recovery effort might use.
Peter Gutman put out a paper about this that can be read at http://www.cs.auckland.ac.nz/~pgut001/pubs/secure
that explains it better.
Though with remapping and newer recording techniques things change and software only erasure becomes more and more problematic. At the highest levels of secrecy I believe most governments require over-kill levels of outright hardware destruction.
the product is stupid (Score:4, Insightful)
The obvious solution: encrypt everything that hits the disk, keep the key in RAM, and overwrite the key when needed.
I'd worry the most about antenna shapes and sizes and various analog circuitry.
Parent
Read the article more closely! (Score:4, Interesting)
Parent
Re:the product is stupid (Score:4, Informative)
I work on UAV's, so we have to care about this a lot.
Check out some of the standards:
DO-178B [wikipedia.org]
Or STANAG 4044, but I don't have a good link.
Parent
Re:the product is stupid (Score:4, Interesting)
Parent
Re:the product is stupid (Score:4, Interesting)
My parents worked at (met at) a secret radar research site (the misleadingly named TRE - Telecommunications Research Establishment) during WW-II. My mom once mentioned that since it was known that in case of lost aircraft there was a real danger of some of the equipment falling into enemy hands, it was routine practise to include dummy circuitry and sometimes wholly bogus equipment just to add to the confusion. Sometimes such equipment was deliberately allowed to be "captured".
A slight weight penalty, but deemed worth it.
Parent
Re:Joe does it (Score:5, Insightful)
Instead of worrying about residual magnetism which can at best be detected by government agencies with extreme funding, people should simply never write unencrypted confidential information anywhere. This also protects you in cases where you didn't schedule the removal of a harddisk, i.e. theft.
Parent
Wrong (Score:5, Informative)
Plus, some people have called into question a lot of the sources used in that paper. It seems that some of the sources don't even exist.
Parent
Re:Joe does it (Score:5, Informative)
Let me correct that: There is no way in this universe software can recover anything from a disk overwritten once with zeros. It is fundamentally impossible.
Also to Peter Gutman's paper: It is still relevant, but the technology has changed. Gutman is very relevant for things like floppy disks (that can hold 100MB, but are used only for 2MB). But todays HDDs go so close to the limits of the amount of data that can be physically present on a disk (as dictated by S/N ratio and surface area), that even a single overwrite with random data may be completely unrecoverable with any technology. Nobody really knows.
Parent
Interesting stuff (Score:5, Informative)
Parent
In related news . . . (Score:3, Funny)
Dozens of prank hard drive erasing have occurred within the Georgia Institute of Technology's nerd population. This was preceded by large orders of extremely powerful magnets. When questioned, the victims only had this to say:
"Khaaaaaaaaaaaaaaaaaaaaaaan!"
not good enough.. (Score:5, Funny)
Re:not good enough.. (Score:5, Funny)
Parent
First question: (Score:5, Insightful)
Re:First question: (Score:5, Informative)
Strong encryption algorithms with suitably long key lengths will take longer than the lifetime of the sun to crack (barring the possibility of quantum computing taking off).
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Re:RISK of quantum computing taking off (Score:4, Insightful)
The way that one-time-pads work, if "attack at dawn" is a possible result, then so are:
attack at dusk
eat more veges
Where's Waldo?
hoist the sail
What you say!!
Zerowing Rules
Do you get it?
search google.
Cryptonomicon.
This is ending
Game is ending
Fire is ending
Heat is ending
What is ending
Iraq is ending
USAF is ending
It isnt ending
Now, which one was the correct decryption?
The reason a one-time-pad is "completely unbreakable", even resisting brute-force cracking, is that every possible string of length X is a valid decryption result for some key. So without knowing the "correct" key, it is impossible to recover any part of the plaintext. The four character ciphertext "sjrw" could decrypt to any of the following strings, even if you found my working paper and were able to deduce that the first two letters were "go":
golf, gods, gore, gold, gone, gout, goal, goad, goat, gosh, goog, go.., go??
No plaintext has higher probability than any other of being correct...
Parent
Re:First question: (Score:5, Insightful)
Heard often, that is an urban myth and nonsense. There is proven secure encryption that is impossible to break, unless the assumption that you can generate secure (i.e. random) keys and some other very simple ones are wrong. ElGamal has this property. Even for less secure ciphers, the statement is untrue. Sure, a single cipher may have weaknesses that may allow a break with high (and often prohibitive) effort. Just use two different ciphers with independen keys and the problem becomes exponentially more difficult since you now need to find a joint vulnerability.
Of course there is a lot of bad encryption on the market, like home-brewed, not peer-reviewed ciphers. Ciphers are also often used in an insecure way, see, e.g., the very good ECB example here: Wikipedia [wikipedia.org]
But the basic problem can be solved. There is just a lot of ignorance.
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Re:First question: (Score:5, Insightful)
Given Moore's law, and assuming it holds beyond physical limits, the expression "billions of years" accurately describes the length of time required to brute force a 4096-bit key.
Given the possibility of quantum computing, the only thing you can do is use one-time pads for all your needs, provided you need these things to stay secret for more than the 50-100 years required to develop quantum codebreaking systems.
Now, that solution is quite feasible, but time-consuming. Here's how you'd do it:
1. Have a secure [D]RNG fill a hard drive to capacity. Copy that to the plane's hard drive.
2. Have a filesystem that writes raw data to the disk--you only want one file containing all data that's collected, and that should be append-only.
3. Instead of simply writing data, XOR the block you're writing with the one that's currently on disk.
4. Once you're back on base, another XOR gets your information back.
Parent
It's really simple... (Score:5, Funny)
Why not use flash memory? (Score:5, Insightful)
Or, just encrypt the data with the key in RAM. (Linux can already do this with swap - it's completely transparent to the user, and the key only lasts as long as the system remains running).
What a crock... (Score:5, Interesting)
What a crock of crap. That and the rest of the story.
I worked in the military long enough to know that they would have encrypted sensitive data as a requirement (destroy or erase a security token, in the use of a combined token/passphrase crypto system and the data is safe) and that the military already use storage devices which can be erased in seconds with a function specifically built just for that.
This story sounds like it is just trying to inject some life into the stock price of some crap company that provides too little, too late.
Re:What a crock... (Score:4, Insightful)
Those guys are a laugh riot.
Parent
Re:What a crock... (Score:4, Insightful)
Yes Francis Gary Powers over flew the Soviet Union and was shot down. Never said he didn't
The EP-3 was in international airspace and was rammed by a Chinese fighter.
How is one anything like the other?
BTW according to international law it is illegal to shoot down an aircraft just from intruding into your airspace. There has to be a clear threat involved. Every attempt has to be made to contact the aircraft and to escort the aircraft to a landing field. There is an entire protocol worked out.
Russia did have at least a marginal case that the U-2 was a threat since it was so far in it's airspace and overflying military sites.
Parent
Fluff (Score:3)
"We developed a 125 rare earth magnetic eraser with self contained power source"
Interesting, but adding in this US spy plane angle has got to be simply PR.
Erasing, not Voodoo (Score:5, Interesting)
You DO NOT have to overwrite a file 35 times to be "safe". This number originates from a misunderstanding of a paper [auckland.ac.nz] about secure file erasure, written by Gutmann.
The 35 patterns/passes in the table in the paper are for all different hard disk encodings used in the 90:s. A single drive only use one type of encoding, so the extra passes for another encoding has no effect at all. The 35 passes are maybe useful for drives where the encoding is unknown though.
For new 2000-era drives, simply overwriting with random bytes is sufficient.
Here's an epilogue by Gutmann for the original paper:
Re:Erasing, not Voodoo (Score:3, Insightful)
Of course, the bad sectors that get transparently reallocated leave dead sectors that can probably be recovered and would not be wiped with stock firmware, so it's academic anyway. If you can't take that risk, you have to turn the media inside the drive into molten slag. There's no other way.
Re:Erasing, not Voodoo (Score:4, Interesting)
That's not what the text you quoted said, nor is it correct. It's true that overwriting 35 times doesn't accomplish anything more, though. The quote said:
For new 2000-era drives, simply overwriting with random bytes is the best you can do [from software / without breaking the drive]. That's because the firmware makes it almost impossible to 'securely' erase data from the drives, so you just can't do any better. It's nowhere near 'sufficient'; in fact it's almost useless against any modern hardware analysis. (The best you can do, if you don't want to keep the drive, is to heat the platters until they melt; that is guaranteed to destroy the data, but almost everything else isn't).
The other important part of the quote is:
This is true, but more commonly you've got several Gb of sensitive data, and the 'enemy' manages to recover some percentage of it. There are companies who do this stuff on the open market - you send them your drive, pay a figure on the order of several thousand dollars, and a while later they send you back most of your data. Their customers tend to be law enforcement, divorce lawyers, private detectives, and companies who are big enough to afford it but not big enough to have a proper backup system in place for their laptop hard drives. They don't need to recover 100% of the porn that has been in your browser cache, just a few pages from some of the sites.
Parent
Re:Erasing, not Voodoo (Score:5, Interesting)
The big problem is that the firmware can remap the physical layout in any way it likes. There's no guarantee that the sector 5 you just wrote to is the same sector 5 you wrote to six months ago - the only guarantee is that if you write some data to sector 5, and then later you ask for sector 5 back again, you get back the data you wrote. Successive writes aren't necessarily placed in the same location. Flash memory is notable for rarely putting two writes in the same place, but hard drives do it too (just not so often). So far as I know, the current desktop drives only remap for reliability and not for performance... but that's quite bad enough (and it seems likely that they'll start doing it for performance sooner or later).
A secondary problem is that secure erasing requires knowledge of the physical layout (to know what sectors and pattern to write in - you may need to overwrite the adjacent sectors in both directions, depending on how the disk is laid out, but which ones are they?) and the firmware hides that information.
There may be others, those are just the ones I'm aware of.
Parent
Re:Erasing, not Voodoo (Score:5, Interesting)
That may be true at some point in the future but it currently is not, and won't be without radical changes in the storage method. There must be a certain amount of tolerance in the current systems in order to compensate for drifting effects. The problem is that if you magnetise a surface such that there are two fields with opposing polarities next to each other, they will over time drift together and kinda-sorta cancel each other out (or at least, you will no longer be able to tell which one was where). So that hard drives keep their data for some number of years, the fields have to be sufficiently strong and spaced out for the drive head to still be able to identify them after they have sat there for a year. That means the head is writing strong, clear fields, and then after a few months it reads back a weaker, fuzzier field.
Now, if the head then writes a strong, clear field over the top of the fuzzy one... then there will be residual traces of the fuzziness in the space between the clear fields. Forensic analysis can use a far more expensive and accurate device to read the fields, and so it can spot several generations of this stuff - it's like a buildup of sediment.
That's not the only possible technique (I don't know which one the professional data recovery companies use), but it's one that drives based around the current methods will always suffer, simply because they must have those tolerances. You can't build a drive where the residuals are completely unreadable, because it means your data will be unreadable after a few months - you have to allow enough for the data to be readable, and that means that residuals can be readable too. Anywhere that you have tolerances like this, you can build a device with a finer tolerance and discover more data.
Parent
DMCA! (Score:5, Funny)
Easy solution (Score:5, Funny)
If the burning is a problem, just make the platters from cheddar cheese, and add a mouse in a cage adjacent to the drive. Open the hatch, and problem is solved.
Not really new (Score:3, Interesting)
Other Georgia Tech innovations (Score:5, Funny)
They have also designed a novel camera which, instead of a digital CCD array, uses a tough, thin strip of polyester polymer coated with a chemical, light-sensitive substrate. Intended for spy applications, if caught the captured images can be destroyed in seconds simply by opening the back of the camera.
Re:Other Georgia Tech innovations (Score:4, Funny)
Parent
How do you read a thermited platter? (Score:5, Interesting)
Besides, shouldn't all the data vanish due to the reaction bringing the surface above the Curie temperature?
Sounds fishy to me (Score:5, Insightful)
There is a second problem with degaussers: You have to physically remove the disks from their housing. That may take more than minutes.
And there is a third problem with degaussers: You have to very carefully check they work with each device they are to be used on. For example, older degaussers do fine for older disks, but are completely useless for modern ones.
And a 4th problem: Degaussers do not work at all for solid-state disks. Since they are not that uncommon in military application and actually may look the same, that seems to be a serious problem. One that encryption does not have.
I see one advantage for the permanent-magnet solution in military application: It works without power. But if you use the encryption-in-the-cable approach I described above, you can keep the key in a battery-buffered memory chip and erase that securely using the power of the battery (not quite as simple as it sounds, but it is possible to do). All in all, this mainly seems to be a scheme to sell the military something expensive.
China?? (Score:5, Insightful)
China may have different attitudes and morals standards than the US, but they are doing many things right as well; more than western media tends to portray (e.g. according to the CIA world factbook [odci.gov] China has a lower percentage of citizens suffering from poverty than the richest country in the world (namely the US)). I don't want to whitewash anything, but reading things like "undeclared enemy" in a tech article on an international website just pisses me off.
Not a spy plane! (Score:5, Informative)
Re:Wrong word? (Score:3, Informative)
Re:New technique? (Score:4, Funny)
Step 1. In emergency, overwrite data with Chinese porn.
Step 2. Actually, there's no need for step 2.
Parent
Degaussing Technique (Score:5, Informative)
I'm most familiar with procedures for erasing magnetic tape than hard drives. The conventional method that I was always taught was to put the tape very close to source of a strong alternating electromagnetic field (so easy way is to just have a small coil hooked up to the wall socket). Then -- and this is the important part -- you move the media away from the coil, while the coil is still operating. So it goes from the near field out to where the field is basically no longer having any effect, but without the field going off. The result is that different layers of the media end up with different magnetic fields: as the media moves further and further away from the coil, the field is no longer able to saturate the center of it, so it's left with a certain state. The material just next to that gets left with a different state, because by then the coil's field has changed directions. So you end up with different magnetic states (polarizations) being written to the media both in the depth direction, and lengthwise (as you pull the tape along past the coil). I guess the thickness of the "stripes" would depend on characteristics of the media, plus the frequency of the coil's field and the speed with which the media was moving past it. I just always moved it slowly away at a few inches per second, personally.
Just holding the media next to a magnet, even an AC electromagnet, and turning the magnet on and off, doesn't erase the data as effectively as moving the media from close to the coil to far away. Or at least that's what I was always told. I suppose if you had a circuit that powered down the coil slowly, it would have much the same effect.
Parent
Re:Degaussing Technique (Score:5, Interesting)
It wouldn't, but you're nearly right. Simply placing a conductive object inside a magnetic field does nothing at all. In order for something to happen there must be motion. When you're using a coil powered from regular mains AC, the power resembles a sine wave, so the field is oscillating back and forth - this is sufficient to have a small effect, but you really want to move the object relative to the coil or you're mostly wasting power (and unlikely to stop the media from working, using a little coil like that). Specifically, the object needs to move across the direction of the field, not along it. A regular coil has field lines that move out from the top of the coil, move around it in a circle, and meet again at the bottom of the coil - so the overall shape in three dimensions is like a torus, with the hole going down the centre of the coil. So you want to move the object repeatedly towards and away from the side of the coil; that cuts the field at 90 degrees, which is where you'll get the maximum effect.
Powering down the coil slowly accomplishes nothing directly - it's not about changing power levels. If you want to make the coil have a stronger effect without moving anything, you need to oscillate it faster, but that's impractical. Just move the media towards and away from the coil, in close proximity, a few times. Speed doesn't matter much, but the power developed by the coil and the length of time you spend doing it does. Moving the media towards the end of the coil (where the hole is) does very little; moving it towards the side is best. However, if you want to actually *remove* all traces of magnetism from something, then you do want to gradually reduce the power level - you see this most often in a monitor's degaussing coil. This may be necessary for tapes and floppies, if the drive can't handle media that has been randomly magnetised and you want to use the media again, but it's not required if you just want to wipe the data before disposal.
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Re:New technique? (Score:5, Informative)
Poster wrote:
If you had read the article , you would have found that they ARE using magnets to wipe the hard drives. FTFA:
Parent
Re:There's powerful and then there's powerful... (Score:4, Funny)
agreed, but its obvious that the original poster never read TFA (or they were doing a TFAD :-)
Well, I can't see too many people getting excited over porn featuring pirates myself, but "arrrrgh, matey, to each their own ..."
Parent
Re:New technique? (Score:5, Informative)
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Re:New technique? (Score:5, Informative)
Parent
Re:New technique? (Score:5, Funny)
What about a magnetic hammer?
Parent
Re:Thermite... (Score:3, Informative)