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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."
"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
Windows has detected an undetectable error.
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 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.
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Poster wrote:
If you had read the article , you would have found that they ARE using magnets to wipe the hard drives. FTFA:
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.
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.
Most ACs are not even worth the keystrokes to insult them. Be generically insulted by this and ignored otherwise.
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).
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.
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.
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.
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.
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