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

Computer systems and their hard drives

[Anonymous Coward]

can be rendered inoperable in seconds - the method's name is "slashdotting".
 
How curious that the anti-bot please-type-in-this-word word is kilobyte for this post.

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.

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

[Anonymous Coward]

Threat is combination of assets and risks. The amount of risk is often a funtion of the value, or percieved value, of the assets, but that generality is proved invalid when bored kids are involved, or the attack is particularly simple.

In term of data on hard disk, there are three circumstances. First, a person may not protect the asset, i.e. not erase the hard disk, and a bored kid then rummages throughthe harddisk. Second, a user may not understand what erase means. There was a time when erase simpley meant change a bit in the file table and mark the space as free. Unerase was then simply a matter of resetting that bit, and then seeing what data as left. Again, the bored kid would unerase and rummage. This has gotten better with the two stage trash can/erase, but can stil be a problem. Both of these are simply solved by a hard disk wipe, as the bored kid will not spend hours with a hard disk, especially when the asset is of no value.

If the asset is of value, all bets are off, and the third case is in effect. If the data is of value, or is incriminating, then the scenario of the parent takes effect. Risk is increased not only because exposure has personal consequences, but there is a specific attacker looking for specific things. In the case of the story, the specific attackers has significant resources to throw at the problem. This was not some bored kid or some local PD on a fishing expedition. Therefore any shortcut trick that did not destroy the integrity of all the data would be insufficient. The attacker has at lesat the resources of the defender. This is the same problem with missle defense. Defense is much more difficult because it must defend against all threats.

So the permamanent magnet seems effective and elegent. It does not require the vaguaries of matching a wipe with specific recording formats. It restores the suface to baseline radomness, perhaps for real. Even normal destruction is often insuffiecent. I once heard a story where to destroy a secret paper one had to burn it, crush the asses, blend it in water, dye it, and who knows what else.

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.

Re:Joe does it

[Mr. Freeman]

Actually, people do know. They've tried it and it works. People have been able to recover data up to something like 2-4 overwrites and it's theoretically possible up to something like 5-7. However I believe this "theoretical" limit requires millions of dollars in technology.

Re:Joe does it

[DamnStupidElf]

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.

That depends on how much attackers know about a given drive. If they can rewrite the drive firmware to give raw access to disk tracks and sub-track positioning, there's a lot that can be done in software without opening the drive.

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.

Hard disks are very far from any theoretical maximum in magnetic storage for a few reasons. The first is that the read/write heads are moving very fast and are roughly linear in nature, e.g. they use tracks and can't analyze 2D regions on the disk as well as a stationary head could, or a head free to move in two dimensions over a point on the disk. Second, hard disk drives must have a very low error rate which means that any recording and subsequent reading must have a high redundancy both in terms of information theory and track width. Basically, the technology that allows a 100GB disk to move tens or hundreds of TB of data over its lifetime with little or no data loss provides plenty of redundancy to read at least some data that is partially overwritten with random data. Third, increasing data density available per disk platter directly implies that at least the older platters were not using anything close to the theoretical maximum of the media. Some data density comes from the magnetic property of the platters, but a lot more comes from the read/write heads and new encoding schemes. With each advance in head technology, it becomes much easier to read more information off existing platters, making data recovery easier.

There are a couple practical reasons simply overwriting a drive doesn't work very well. The first is that simply overwriting each sector on the disk with random data is not truly random. The error correction codes for the sector are still valid, which means that all the data on the track is predictable, making it easier to recover what was on the disk before. Since both the original overwritten data and the new "random" data are mathematically related, it is much easier to reconstruct the original data. Some drives have modes to access the raw tracks directly, and this mode could theoretically be used to write random data over the entire track, including ECC areas. It would also allow remapped sectors to be overwritten. Generally, after a sector has required error correction to be applied more than a set number of times the data is remapped to a set of spare tracks reserved for that purpose. Without raw access to the disk, there is no way to overwrite the original data from these remapped sectors which are still able to provide the correct data after error correction is applied.

Re:Joe does it

[zaphod_es]

You may be correct but you are only talking about current technology. When you are dealing with the most sensitive data involving governments and the miilitary you have to be pretty sure that the data cannot be reconstructed in five or ten or even fifty years time. Some of the more extreme suggestions for destruction of disks do not seem so silly in that context.

Re:New technique?

[ballermann]

FTFA: The researchers concluded that permanent magnets are the best solution.

In related news . . .

[UnknowingFool]

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..

[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:

[nottestuser]

Because the Windows 98 computers running the spy cameras don't support encrypted file systems.

Seriously, this is a fricking no-brainer. Make the key 4096 bits of random data, load it into battery-backed RAM from a storage device kept at the air field. When you run in to a problem you have 4K of data in RAM to destroy instead of GBs of data on disk with the added benefit that if you ever get the disk back to the air field you still get your data. Unless the Air Force doesn't have access to unbreakable encryption...

Re:First question:

[SagSaw]

Why wasn't the content of the harddrive encrypted?

Encrypting the harddrive (which it may have been) simply changes the problem from one where you need to destroy the unencrypted information quickly and compleatly to one where you need to destroy the encryption key quickly and compleatly. Destroying the key may or may not be any easier that destroying the data depending on how it is stored. Also, even if the data is encrypted and the key compleatly destroyed, you probably still want do destroy the encrypted data. After all: How sure are you that your enemy hasn't found a way to break your encryption or somehow obtained a copy of the key?

Re:First question:

[bwd]

I would imagine that the plane was recording enormous amounts of data, both video and otherwise. Streaming all of that to a satellite in real time would not be practical. I'm sure that those large spyplanes were recording significantly more data than a predator drone.

Re:First question:

[Takumi2501]

In most cases, I would tend to agree with you.

At the present level of computing technology, a brute force attack on such a key would take waaaay too much time to be practical, but you have to consider the length of time that you want to keep this data secret, and how much processor speed will improve within that time span.

Damn you Moore!

Note: Yes I know that Moore's law refers to the compexity of integrated circuits, and not their speed.

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:

[gweihir]

Actually, No matter what cipher you'll be using or how large the keys you're using are:
One can always use brute force to find a solution.

P.S.: And before I forget: This is wrong as well unless you can do a known-plaintext attack (i.e. cheat). If you do not already know what the plaintext is, there is a minimal amount of ciphertext and knowledge you need. And it needs to be more than the entropy in the key. If it is not, you cannot brute-force it. For example the Enigma is completely secure, unless you encrypt more than about 4kb of german text with a key.

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:First question:

[Anonymous brave dude]

umm, it's 10443888814131525066917527107166243825799642490473 83780384233483283953907971557456848826811934997558 34089010671443926283798757343818579360726323608785 13652779459569765437099983403615901343837183144280 70011855946226376318839397712745672334684344586617 49680790870580370407128404874011860911446797778359 80290066869389768817877859469056301902609405995794 53432823469303026696443059025015972399867714215541 69383555988529148631823791443449673408781187263949 64751001890413490084170616750936683338505510329720 88269550769983616369411933015213796825837188091833 65675122131849284636812555022599830041234478486259 56744921946170238065059132456108257318353800876086 22102834270197698202313169017678006675195485079921 63641937028537512478401490715913545998279051339961 15517942711068311340905842728842797915548497829543 23534517065223269061394905987693002122963395687782 87894844061600741294567491982305057164237715481632 13806310459029161369267083428564407304478999719017 81465763473223850267253059899795996090799469201774 62481771844986745565925017832907047311943316555080 75682218465717463732968849128195203174570024409266 16910874148385078411929804522981857338977648103126 08590300130241346718972667321649151113160292078173 8033436090243804708340403154190336
different keys.

Re:First question:

[DrAegoon]

The one time pad idea has merit, but there are a number of problems with it. First, there is the logistical nightmare any one time pad system causes. Since each pad can only be used once a new key must be produced for every hard drive on every mission. Securely distributing all these keys brings up the same problems as protecting the data itself.

These problems can be addressed, but a one time pad cannot prevent the problem in the article since it only works for data produced while in flight. It is far more likely that highly classified data is being carried on a plane like this because it is neccessary to complete the mission. In order to access the data you would need to take the key with you and then you're back to square one because the drive containing the key still has to be destroyed in an emergency.

Finally, since the data is so important to the mission, it needs to be stored on media that is resistant to accidental modification. The device described in the article is meant to address the conflict between the robustness needed to survive a mission and the volatility needed to destroy the data in an emergency. This problem also applies to any in-flight encryption technique where a key is needed to read the data. Even if the key is not stored on a hard drive it has to be stored on something that is resistant to accidental loss.

The product sounds ridiculous because no one outside of government is trying to protect their data from an adversary with effectively unlimited resources. The military doesn't have the luxury of assuming their adversary won't take an electron microscope to the drive to recover overwritten data or determine which bits have been switched from their previous state. That's the kind of threat the technique in the article is meant to address.

Re:Wrong word?

[Tavor]

"Definitions of legion on the Web: * host: archaic terms for army * association of ex-servicemen; "the American Legion" * a large military unit; "the French Foreign Legion" * horde: a vast multitude" via Google's "define" search

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).

Re:Why not use flash memory?

[bcmm]

You're going to want full video of the flight, at a high resolution if possible. That's gonna take up a few GB very fast

Re:Thermite...

[Harmonious Botch]

Actually, it's the iron that comes out molten; the aluminum is tied up as solid aluminum oxide. Nonetheless, it is a good question.

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.

Re:What a crock...

[LWATCDR]

You forgot that the plane wasn't over China but was in international airspace when it got hit by the Chinese jet. You got to love the Chinese claim that a 1950's turbo-prop airliner managed to ram a supersonic jet fighter.
Those guys are a laugh riot.

Re:What a crock...

[LWATCDR]

Umm... And your point is?
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.

Fluff

[Sosarian]

If this isn't a fluff piece I don't know what is.

"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

[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

[ArbitraryConstant]

If data can be recovered after fewer wipes, the people capable of recovering it certainly wouldn't advertise the fact. Extra passes are cheap, the costs of someone recovering data might not be.

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

[asuffield]

For new 2000-era drives, simply overwriting with random bytes is sufficient.

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 any modern PRML/EPRML drive, a few passes of random scrubbing is the best you can do.

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:

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.

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.

Re:Erasing, not Voodoo

[jhines]

If I'm getting paid by the hour, 35 passes is fine by me, and I will watch every single one of them to make sure it really ran. Can't cut corners when it counts.

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.

Re:Erasing, not Voodoo

[DigiShaman]

That sounds nice and all, in theory. But I doubt anyone has ever recovered a file reading residual magnetic fields. Seriously! Just how DO you determain what group of bit/bytes belongs to what generation of residual fields? If you don't know what generation the bits are found on, then threading the data back togeather is meaningless. All you will get is random binary noise.

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:Easy solution

[Mr. Freeman]

That's a good idea.... until you pull 5 Gs trying to avoid an enemy fighter and kill the mouse.

Equip the mouse with a flight suit though, and you're all set.

Re:Easy solution

[modecx]

I think the better solution would be to make the drive platters out of a thermite-cheddar composite. Once the mice eat the cheese we can then ignite the mice for maximum data security.

the product is stupid

[r00t]

Normally the hard drives just go into a grinder or furnace. Sure, that won't suit an airplane, but neither will a bulky magnetic device that weighs 125 pounds per hard drive. (can't just have one because the drive has to slide right in)

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.

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.

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 :)

Re:the product is stupid

[AJWM]

I'd worry the most about antenna shapes and sizes and various analog circuitry.

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.

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.

Not really new

[Dolphinzilla]

Both M-Systems and Memtech have solid state disk drives that implement NSA and NISPOM approved methods for secure hard drive erase - and they can erase the entire drive in under a minute -

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.

Re:Other Georgia Tech innovations

[Dynedain]

How can that be news? The shrinter is already available from thinkgeek.

Re:New technique?

[Wonko the Sane]

If you shape the magnets correctly and use AC to power them, then a magnetic field can (in theory) move any material that conducts electricity. Because a moving magnetic field will generate an electric field in the conductor, with will create a magnetic field that interacts with the original field. It may not be practical with all materials, but it is possible.

Forget the secret information

[sk999]

the researchers designed a neodymium iron-boron magnet with special pole pieces made of esoteric cobalt alloys.

Sounds like the magnet may be worth more than the secret information it is supposed to protect.

Wiping disks...

[Gordonjcp]

... by overwriting twice with random data will destroy any data beyond recovery. You can't use special things to read residual magnetic data off the platters, unless you're habitually using 25-year-old hard disks. Modern drives use very complicated modulation schemes, unlike old MFM drives.

Comment removed

[account_deleted]

Comment removed based on user account deletion

DRM

[elgee]

Now the RIAA/MPAA/FUD are going to demand that such a device be put into every possible digital recording device.

Attempt to copy a protected product and BAM, your hard drive is toast.

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.

Re:Drill+Thermite?

[Oggust]

I know by itself thermite and similar methods have difficulty penetrating the outer case reliably, but I would think drill+thermite injection to fill the internal cavity of the system would be effective..

Takes too long to drill the disks and insert the thermite, while your spy plane is spiralling down.

And anyway, if the themite didn't fully destroy the disks, you weren't using enough of it. See?

/August.

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!

There's powerful and then there's powerful...

[Animaether]

GP probably meant by 'powerful' magnets the kind you can get at scientific supplies shops, or even (in slightly less powerful degree) at ThinkGeek.

The 'powerful' in the article refers to the power akin to an MRI scanner. Ever see that video of somebody holding a scissor on a string several feet away from the aperture, and the scissor points straight to it with some duress on the holder's finger from the string when the MRI is on?

Suffice to say that nobody in a home/office environment is going to have one those 'powerful' magnets laying around.

Me - I settled for "Darik's Boot and Nuke" as part of the Eraser program to wipe two old computers, and will again for a third shortly. They never had highly classified or particularly sensitive information - just stopping the casual users from retrieving old porn. I hate porn pirates.

Re:There's powerful and then there's powerful...

[tomhudson]

agreed, but its obvious that the original poster never read TFA (or they were doing a TFAD :-)

I hate porn pirates.

Well, I can't see too many people getting excited over porn featuring pirates myself, but "arrrrgh, matey, to each their own ..."

Re:There's powerful and then there's powerful...

[Dining Philanderer]

Holy crap dude, If you hate porn pirates then you hate EVERYONE!!!

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?

[eqisow]

What I want to know is, is it more effective than a really big hammer?

correction

[slashdotnickname]

it happened in 2001 to a US spy plane over an un-declared enemy (China, and that's a topic in itself).

This is offtopic, although a more interesting topic than "wiping data", but the plane itself was over international waters and never over China's territory.

Also, since when does spying require a declaration of war? The whole point of spying is to aid in deciding-the-need-for or course-of preemptive actions. Given the Chinese government's penchant for secrecy and censorship, it seems fair to want to keep an eye on them. The same point can be made about spying on any other country... everyone knowing what everyone else is doing has a stabalizing affect. All bad decisions are made in fear, which brought on by ignorance, and governments, whose decisions affect millions, need all the tools possible to make correctly informed decisions.

Not in your wildest dreams.

[Ivan Matveitch]

Good trade relations with the United States are critical to the party's survival. If western markets became inaccessible and foreign capital fled, growth would falter, internal tensions would mount and the legitimacy of the party would soon be questioned. In any case, a global hyperpower can do just about anything it wants: weaker states must submit to its overwhelming might. And none of these rulers seek justification in your eyes.

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:China??

[dave1212]

China is the biggest threat in the world to these rights.

Funny, I was sure that was the USA. Clean up your own damn backyard before focusing on other people's problems.

Re:China??

[Beryllium Sphere(tm)]

>>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?
When your spy plane is making an emergency landing because another country's fighter just rammed it, it does take a while to start thinking of that country as a friend again.

Re:I've got a near-flawless erasure method.

[gweihir]

Go buy a nice 3" diameter 1" thick n50 Neodymium-boron magnet. Condiering it's strong enough to attract steel pots and pans from ten to twenty feet away, just setting one of these bad boys on a hard drive will almost 100% efectively wipe it the fuck out, not to mention most likely fuck up the heads on the drive, making it totally useless.

Also it will keep the plane attached to the steel in the concrete of the landing strip and thereby prevent it from falling into the enemies hands in the first place. A sound engineering solution!

China is not an enemy

[linuxrocks123]

> ...undeclared enemy (which is China, and that's a topic in itself).

China is not an enemy. We buy a ton of stuff from them. They buy a ton of stuff from us. Our businesses have offices there. Our colleges have exchange programs with them.

Yeah, our diplomatic relations are a little bit strained over things like Taiwan, but we're nowhere near going to war with them. If you're a troll, shame on you. In any case, shame on the Slashdot editors for choosing this ignorant or trolling person's story.

Re:New technique?

[fish waffle]

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

What about a magnetic hammer?

you read the article more closely!

[r00t]

Sure, they say they will get the weight down. OK, maybe they cut it in half.

They do need one device per drive. You missed the part about the drive being automatically pulled into the device, and the part about a twist handle as a backup.

In other words, this is a drive enclosure. The drive sits in the safe part of the enclosure most of the time, connected to a destruction actuator. Nobody is going to be running around the airplane yanking out drives.

Probably a few drives could go into a mechanically complicated (less reliable) shared enclosure. Doing everything that way is no good. Equipment may come from different suppliers, with different technology. Think of a flying datacenter with rackmount systems from a variety of different vendors. (the prime contractor has to make it all fit, but isn't supposed to do a custom redesign of every subcontractor's computer) Also you have the matter of ongoing upgrades.

Re:you read the article more closely!

[Anonymous Coward]

I actually noticed the part about the drive being automatically pulled into the device. I assumed this meant that someone would eject the drive from whatever console it was installed in, stick it into a slot with warnings and yellow/black striped tape around the opening, and the motor (or hand crank) would draw it in past the magnets. It's possible that the intention is for one of these to be installed behind every hard drive in the plane and for them to get sucked in automatically, but the article isn't specific enough to say either way. Maybe someone will be yanking drives. Unless of course you have information outside of this article that is more specific???

Re:you read the article more closely!

[Doctor Memory]

Think of a flying datacenter with rackmount systems from a variety of different vendors

A variety of different vendors that all have to meet a spec, namely that the drive must be mounted in a non-metallic carrier of such-and-such dimensions. Or just specify that each drive must be mounted in a "Type SZW data carrier", and it's up to the primary contractor (who also supplies the SZWs) to make it all work. Either way, it's all pretty trivial: the Navy wants one of these mega-erasers for its P-3s, so (say) Lockheed figures out they're all using 5 1/4" drives, so designs an enclosure to fit. Navy then institutes an upgrade program for all specified aircraft, and new drives are obtained and installed into said enclosures. Not a terribly complicated retrofit, and for guaranteed security (if they can prove it), I'm sure they can justify the cost. Sure, there'll be a ton of engineering busy-work for somebody, figuring out how many drives are affected and designing the enclosure and associated cabling changes and documentation updates, but that's what new hires are for... ;)

Re:you read the article more closely!

[nacturation]

They do need one device per drive. You missed the part about the drive being automatically pulled into the device

The six disc CD changer in my car pulls CDs automatically into one device. I'm sure this technology will never progress to such an advanced stage though.

Re:New technique?

[Anonymous Coward]

I just have to wonder aloud for the sake of curiosity what effect a (perhaps slightly modified) medical defibrillator would have. Maybe replace the conductive paddles with said electromagnets?

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.

Waste of money

[kimvette]

125 lbs' worth of equipment to securely scramble a hard drive? Let me guess, the contractor is going to spend time "miniaturizing" it and charge several hundred grand per unit, right?

I have a solution, with the total weight being under 5 lbs and total cost being under $130 (not counting any logic/switching required to enable it).

Keep in mind:

  - the aircraft is disabled
  - flight instrument interference is a non-issue
  - The HDD not only does not have to be usable, it is intended to be unusable after this process
  - 12V, 24V, and 48V taps should all be readily available in the aircraft (NiMH batteries would suffice)

Ready?

Here are the required components:

  - a heavy-duty consumer-level inverter costing under $100 in bulk
  - a Radio Trash (or generic) degausser costing well under $30 in bulk.

Total weight: under 5 lbs. Renders a hard drive unusable in a couple of seconds.

Because Flash memory is even worse

[SargeantLobes]

Wouldn't it be easier to use a flash memory chip?

Data on Flash memory (e.g. usb drives) has a tendancy to burn in. The longer it's in there the more it burns in. There's no real way to counter this. The only way to theoretically wipe it is to do several passes each a few weeks apart.

So you'd have to really completeley destroy the drive. which basically means something like thermite, which, as the submitter mentioned, is unsuitable for aircrafts.

Everytime I hear of the milatary using these (and losing them, which they seem to do regularly), it pisses me off. They must have had an IT guy telling to never use that stuff, and to encrypt their data. For some reason the higher ups just seem to not get the point, and they still use it, and leave them behind in their rented cars.

Thermite should work...

[squoozer]

If I needed to destroy a the data on a drive in seconds I would simply heat it well above the curie temperature for the magnetic material being used. If you are feeling really paranoid add a variable field strength magnet as well - once above the curie temperature you wouldn't need much of a magnet to make sure things were well scrambled.

Re:Violation of Chinese airspace

[Dunbal]

What the **** is the US government doing violating Chinese airspace without permission or clearance?

This is an act of war.


      This has never bothered the US before, why should it now?

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:RISK of quantum computing taking off

[michaeldot]

Yes, lines 1, 2 and 4 are correct. They are Slashdot usernames.

Line 3 is obviously a Digg imposter.

Re:New technique?

[Walt Dismal]

I've patented my new technique and offered it to the military.

Step 1. In emergency, overwrite data with Chinese porn.

Step 2. Actually, there's no need for step 2.

Re:RISK of quantum computing taking off

[stoborrobots]

in the real world the data you send does not has many possible outcomes and many of those very few are legitimate. If you try 600 times and you get the text:

oyioa2dsi5fuso
nbvsouydgfvs4f
attack at dawn
90s8 asd0shdks ... etc

I think it's pretty clear which is the correct messae

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...

Nitpick.

[warrax_666]

Make that /dev/urandom or you could end up waiting a loooooong time for it to finish.

Re:yes

[Kreigaffe]

Better yet: Replace 'bogus information' with 'goatse.cx'

Nothing like tricking someone into looking at ol' goatse --- except tricking someone into spending millions and millions of dollars to look at ol' goatse.

Why not use sand

[frambris]

The raptors have a window in its housing letting one can show off the platters. Why not make that window removable and when in need to erase the drive just pour in some sand while it's spinning. That will surely sand of anything magnetic. Or make the heads lower themselves on to the platter and lathe the magnetic layer off. When the magnetic top layer is shaved off into dust the platters are nothing more than metallic frisbees.

"erase" is ambiguous; four kinds of erase

[whit3]

To clarify things, here's several scenarios for erasure:
"delete file" erasure: tell the OS that that part of a file system doesn't have any current ownership,
and that the filename doesn't exist, i. e. doesn't point to any data.
"overwrite sectors" erasure: direct the hard disk drive to put new, noninformative, data into the
spaces formerly occupied by a file's data (and maybe metadata, like the file's icon and such)
"multiple remagnetize" erasure: direct the hard disk drive to put all (in binary terms, both) physical
magnetizitions onto the data area, so that data's remnant traces are not informative
"whole-disk multiple" erasure: ensure that all areas on the hard disk and all other data-holding parts (flash ROM)
are multiply rewritten. This would make the bad-block list disappear, might even make the
original format (how many tracks and sectors) unknowable to an investigator.

After "delete file", unerase software can bring much data to light
by scanning the drive through the normal hardware. Because EVERYONE KNOWS THIS, there
are 'secure erase' options in many disk tools (Norton "Wipe File", Mac OS X "Secure Empty Trash" etc.)

Those secure erase tools do multiple "write-over-sector", but there are some
regulations that require "multiple remagnetize" erasure, and even 'dd /dev/random' isn't
guaranteed there; you gotta pay money for a tool certified for that use. Here's why:

What everyone DOESN'T know, is that "write-over-sector" leaves behind some small regions
(magnetic domains) in places the read/write heads cannot access, which can be sensed by
exotic techniques (optical rotation, neutron scattering, electron beam microprobing). The
erase-35-times and DOD (military) multiple-erase requirements are aimed at this kind of
exotic stuff. Nothing you can do in software would get data back from "write-over-sector"
erasure.

The modern disk drive compacts the data into a serial bit stream of known bandwidth and
containing parity/error correcting code information, and DOES NOT put ones down on the
disk when ones are in the data (MFM, RLL, and suchlike encoding schemes are in use on ALL
media I'm aware of). This embedded-clock-and-data stream is hard to predict (what does
Hitachi use on sATA drives this week? I don't know. Does anyone?), but WITH KNOWLEDGE
of the encoding scheme, there are different recommended patterns for ensuring
erasure to the standard of 'put ones on every spot, then zeros on every spot' . The use of
software with ones in the DATA INPUT is not going to cause ones in the MAGNETIZED PATTERN,
but you can come up with a set of data inputs that DOES effectively hit every bit of the surface.
The famous paper on erasure has thirty-five scenarios for the encoding on the disk,
and attempts to give a full remagnetize (with 'dd /dev/pattern01' through 'dd /dev/pattern35'
kinds of operations).

So, that's a third kind of erase, intended to remagnetize all portions of the disk surface.
The formal requirement to remagnetize the surface is ridiculously strict, becaue the exotic techniques
DON'T KNOW HISTORY. Those random little domains can be left over from the manufacturer's
bad-block scan, or from last December's diagnostic reformat, or from the camera run from last
week, or from this week's most sensitive information, or can be a combination of all of those.

Or, it could be a bit of cosmic ray induced damage. The exotic reconstruction technique
doesn't have any noise margin, it doesn't ignore the insignificant; noise is guaranteed.