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.

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: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!

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.

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! :)

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.

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.

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.

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.