A New Technique to Quickly Erase Hard Drives

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."

Comments

Joe does it

[janet-on]

Unfortunately a few passes with random data is not as effective against a sophisticated recovery effort as is often assumed.
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_ del.html
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.

Re:Joe does it

[Anonymous Coward]

That is mostly urban legend. There is a theoretical possibility that overwritten data could be reconstructed, even several layers "deep", but in practice there is no commercially available service capable of that stunt. If you know of one, name it (with references that they can do it). If they could do it, they would have to have technology available which could instantly multiply the space on these platters. It's not just a matter of having a reader with twice as good a SNR as a standard RW head. The writing harddisk doesn't just add signal, it also adds noise. The SNR on the platter will be barely good enough to read the signal of the last write. Otherwise the harddisk manufacturer could have made a bigger harddisk at the same price. The economics of the situation make recovering a previous write unlikely. The real problem with deletion by overwriting data is that it is really slow. It takes hours per disk.

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.

Re:Joe does it

[gweihir]

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,

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.

not good enough..

[Adult film producer]

When I need to protect my data from spying eyes I secure a 500m sata cable into the back port and slowly, very carefully; feed the hard drive into the event horizon. Giving it a good yank after a few minutes and reeling it back in.. the drive returns to normal working condition afterwards.

Re:not good enough..

[proverbialcow]

I do that with my laptop, but then I always have to reset the clock.

First question:

[fluch]

Why wasn't the content of the harddrive encrypted?

Re:First question:

[Jackmn]

Encryption can be broken. Always.

One time pads cannot be broken.

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).

Re:First question:

[gweihir]

It probably was. Encryption can be broken. Always. Doesn't matter how strong.

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

But the basic problem can be solved. There is just a lot of ignorance.

Re:First question:

[dhasenan]

At the present level of computing technology, the expression "billions of years" pales in comparison to the length of time required to brute force a 4096-bit key.

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.

Re:New technique?

[Anonymous Coward]

Aluminum can act oddly in the presens of magnetic feels. see this link for information on how it might be able to bens platters.

It's really simple...

[Anonymous Coward]

Just use Maxtor harddisk drives, those things destroy themselves all the time!

Why not use flash memory?

[Richard_J_N]

Wouldn't it be easier to use a flash memory chip? It's unlikely that more than a few GB would be needed. And destroying a flash chip is much easier.
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...

[Anonymous Coward]

The Chinese eventually gained access to U.S. military secrets.

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.

Erasing, not Voodoo

[Psionicist]

I would like to take the oppertunity here to debunk a very common myth regarding hard drive erasure.

You DO NOT have to overwrite a file 35 times to be "safe". This number originates from a misunderstanding of a paper 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:

Epilogue In the time since this paper was published, some people have treated the 35-pass overwrite technique described in it more as a kind of voodoo incantation to banish evil spirits than the result of a technical analysis of drive encoding techniques. As a result, they advocate applying the voodoo to PRML and EPRML drives even though it will have no more effect than a simple scrubbing with random data. In fact performing the full 35-pass overwrite is pointless for any drive since it targets a blend of scenarios involving all types of (normally-used) encoding technology, which covers everything back to 30+-year-old MFM methods (if you don't understand that statement, re-read the paper). If you're using a drive which uses encoding technology X, you only need to perform the passes specific to X, and you never need to perform all 35 passes. For any modern PRML/EPRML drive, a few passes of random scrubbing is the best you can do. As the paper says, "A good scrubbing with random data will do about as well as can be expected". This was true in 1996, and is still true now.

Looking at this from the other point of view, with the ever-increasing data density on disk platters and a corresponding reduction in feature size and use of exotic techniques to record data on the medium, it's unlikely that anything can be recovered from any recent drive except perhaps one or two levels via basic error-cancelling techniques. In particular the the drives in use at the time that this paper was originally written have mostly fallen out of use, so the methods that applied specifically to the older, lower-density technology don't apply any more. Conversely, with modern high-density drives, even if you've got 10KB of sensitive data on a drive and can't erase it with 100% certainty, the chances of an adversary being able to find the erased traces of that 10KB in 80GB of other erased traces are close to zero.

Re:Erasing, not Voodoo

[asuffield]

Not to mention that the whole "residuum magnetism" that may actually have existed in 90s HDs isnt simply possible anymore with todays track density. Any kind of remnand from the last state would be well under the paramangetic limit and completely replaced by thermal noise.

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.

Re:Erasing, not Voodoo

[asuffield]

As far as I know, the only limitation that modern firmware places on securely erasing data is smart buffering. i.e. the firmware sees 10 writes to the same sectors in the buffer and chooses to only write the last one to save time. Although that is a problem, modern erasing software ensures that all X amount of specified writes actually get written.

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.

DMCA!

[fluch]

Seal the HD with a sticker that says reading the content of this HD is prohibited by the Digital Millennium Copyright Act. That will show them! :)

Degaussing Technique

[Kadin2048]

It depends on the type of magnetic field used and how it's applied. If you just put a drive platter (or magnetic tape, or floppy disk) into a static magnetic field, you might bend the platters or disturb the media, without actually destroying the data itself.

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.

Re:Degaussing Technique

[asuffield]

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.

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.

Easy solution

[JanneM]

If thermite doesn't do a good job, go one better and make the platters out of thermite. Make the motor axle out of magnesium, add a fuse and you're set.

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.

Re:New technique?

[tomhudson]

Poster wrote:

Powerful magnets do rather little to wipe hard drives

If you had read the article , you would have found that they ARE using magnets to wipe the hard drives. FTFA:

The researchers concluded that permanent magnets are the best solution.

Other Georgia Tech innovations

[dpbsmith]

And in further news, Georgia Tech scientists have designed a printer with an integral shredder that shreds all output continuously as it is printed.

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.

Wrong

[bwd]

The paper you are quoting from is horribly out of date and very little of that applies to modern drives. This post does a good job of explaining Gutmann's more recent comments.

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.

Read the article more closely!

[NixieBunny]

With all due respect, the article doesn't describe the device as you say. It weighs 125 lbs in prototype form, which will be reduced for production, and there's only one needed per airplane, not one per drive. What they're proposing is much less bulky than a similarly useful grinder or furnace. After all, it has to be usable on many packaged drives, quickly, in emergency plane-crash conditions. In a previous life, I did some work for E-Systems on a spy plane (Rivet Joint) using big removable ESDI drives of a few hundred megabytes each capacity, and the project guy said that it took about 20 minutes for their emergency drive erase sequence to finish. Not good if you're going down in enemy airspace!

How do you read a thermited platter?

[vadim_t]

Now, even assuming there's something remaining after thermite, how do you get it out of a molten platter? The head hovers at nanometers from the disk's surface. A bent disk with a huge hole through it will just instantly wreck any head trying to read it. Is it even technically possible to restore the platter to a condition where you can even try to read anything from it?

Besides, shouldn't all the data vanish due to the reaction bringing the surface above the Curie temperature?

Sounds fishy to me

[gweihir]

Degaussers are nothing new. But there is no need to use them. Encryption does the trick as well. Just erase the key securely and you are done. If the device that the disk is installed in does not support encryption, then develop a module that sits between disk and device and encrypt on that. Attach a switch that triggers key erasure.

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.

Re:New technique?

[Cromac]

According to the article, yes it is more effective than a hammer. It said that techniques such as crushing the drive still allowed the data to be recovered, given enough time.

Other methods, including burning disks with heat-generating thermite, crushing drives in presses, chemically destroying the media or frying them with microwaves all proved susceptible to sensitive, patient, recovery efforts.

China??

[nephridium]

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)

What's with all this hate mongering against China? Why was this totally OT snippet even up there anyway? To keep us reminded that there are "bad guys" out there and when we think about harddisks we also should be completely aware that we should be afraid, very afraid of an "undeclared" enemy?

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 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.

Re:Computer systems and their hard drives

[Anonymous Coward]

Anyone that has watched enough Hollywood movies knows that it is usually enough to shoot a couple of bullets into the monitor to destroy all sensitive data.

You never have to worry about arcane details such as hard drives, magnetic field strength etc etc.

Re:New technique?

[fish waffle]

According to the article, yes it is more effective than a hammer.

What about a magnetic hammer?

Re:the product is stupid

[Anonymous Coward]

You might be glossing over the flight critical requirement though. "Keep the key in RAM" is likely not something that would be allowed.. or incredibly hard to get certified. Would have to prove (which is harder than just showing) that while in flight, there was no way the key could get lost, or changed, or ... such that the software could get locked down in flight. I don't think that it would be impossible, just that the hoops you might have to go through may make other options more attractive.

I work on UAV's, so we have to care about this a lot.

Check out some of the standards:
DO-178B
Or STANAG 4044, but I don't have a good link.

Not a spy plane!

[Bowling Moses]

The US aircraft alluded to was a US Navy EP-3E Aries II, a slow four-engined turboprop plane based on a passenger airliner. It's a surveillance aircraft, not a spy plane. It's out in the open, in international airspace (usually), and a modern military will immediately pick up on where it is and what it's doing. It's completely dependent on international treaties to not get shot down by whoever it's checking out. A SR-71 or U-2 on a secrete high-altitude flight over a hostile nation it isn't.

Interesting stuff

[TheSpoom]

I have commonly heard it said that overwritten data can be recovered, so I went Googling for a rebuttal to this argument. Turns out, you appear to be right! Recovering of overwritten data is largely a myth. /me continues to use good ole' shred.

Re:the product is stupid

[FluffyG]

I'm a LAN integrator for a mobile military communications system that is used for passing of secret and top secret material... Our manual says it takes about 3 grenades in the hummer to format all the hard drives if they need to do it quickly :)