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Can I erase sensitive data on an old hard drive with Neodymium Magnets?

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Re: Can I erase sensitive data on an old hard drive with Neodymium Magnets?

#101

Post by zkms »

Lramseyer wrote: post #85

I worked in the HDD industry, doing signal processing for a few years. HDDs are pretty much magical. It's insane how delicate, yet robust it all is. But to put things into perspective with some numbers, the write heads on a modern HDD use somewhere on the order of 50 mA of current. That may sound like a reasonable amount until you consider that the magnetic field [flux] is condensed down to a 60 x 20 nm area. It usua…

> HDDs are pretty much magical. It's insane how delicate, yet robust it all is.

Absolutely. It's bloody amazing how my laptop has a device with finger-sized actuators that read/write bit cells that are about as small as couple-year-old semiconductor feature sizes -- and that can survive mistreatment that one doesn't usually associate with micromanipulators.

Re: Can I erase sensitive data on an old hard drive with Neodymium Magnets?

#102

Post by crx087 »

abrookewood wrote: post #88
mark-r wrote: post #23

Is it really necessary to overwrite the data multiple times to erase it? With the densities provided by today's hard drives, the techniques you used to be able to use to get partially erased data are routinely used by the disk drive itself for normal reads.

It's totally not required to wipe it/over write it more than once. I wish I could find the reference, but someone made a fairly comprehensive attempt to read data that had been over written once and they couldn't detect anything.

Not true, at least not under many conditions.

The required equipment makes magnetic data unlikely to be recoverable except in exclusive cases where certain government agencies with sophisticated labs get involved, but in short, storage leaves lasting (trace) physical changes behind.

SSDs and operating systems without proper Secure Erase support can very easily leave behind complete data.

Re: Can I erase sensitive data on an old hard drive with Neodymium Magnets?

#103

Post by akvadrako »

derefr wrote: post #86
akvadrako wrote: post #39

Earlier quoted context omitted.

Well your password could be brute-forced unless it's really long and random (about 20 chars). There might also be flaws in the encryption code. And changing it later won't work, because old sectors might still be recoverable, even if they are overwritten.

Usually with full-disk encryption, your supplied encryption passphrase is used to encrypt a single sector (or redundant set of sectors, spread across the disk) containing a much larger master key, which is in turn used to encrypt the rest of the sectors. When you change the disk password at the OS level, the master key remains the same (which is why you don't have to wait for the disk itself to re-encrypt); the singl…

You can overwrite a physical sector in modern drives, at least not in a standard way. That’s because they contain internal controllers that map physical to virtual sectors.

Re: Can I erase sensitive data on an old hard drive with Neodymium Magnets?

#104

Post by zaarn »

Scramblejams wrote: post #45
2muchcoffeeman wrote: post #41

Earlier quoted context omitted.

Yeah, I hope people realise that everybody has these magnets IN their computer. You might have a NAS in which case you have several of these magnets much closer than 6 inches to the other drives and power supply and nothing happens. Magnets near your or even on the computer do nothing.

Magnets induce a current when moved relative to a conductor. The magnets you mention aren’t moving.

When you swap drives, they are. Yet people don't have mysterious data loss when swapping drives out of their bays.

Re: Can I erase sensitive data on an old hard drive with Neodymium Magnets?

#105

Post by zaarn »

zaptheimpaler wrote: post #9
tscs37 wrote: post #4

If you want to get rid of a harddrive with sensitive data I would first suggest that one gets familiar with the thought of not being able to sell it as used. Personally for my drives, I use Boot and Nuke to erase the drive three times, first with zeroes, then with random data, then with zeroes again. After that I disassemble the drive, put a strong magnet over each platter, shredder the drive into almost powder, burn…

All that effort just to get rid of some hentai...

Atleast it won't resurface as incriminating material 10 years down the line or something.

Re: Can I erase sensitive data on an old hard drive with Neodymium Magnets?

#106

Post by zaarn »

allenz wrote: post #63
magnat wrote: post #3

Hard disks are surprisingly hard to destroy on-demand. There was a DEF CON 23 talk [1] exploring ways to quickly wipe your servers in situ using physical methods. [1] https://www.youtube.com/watch?v=-bpX8YvNg6Y

Entertaining talk, but the best method is to discard the key for your fully encrypted disk. It's 2017, all your disks use FDE, right?

SSDs internally yes. Any modern SSD simply uses some random key unless you specify another one. Shredding is as simple as telling it to shredder the key, end of story.

Some harddrives do this too, I believe but it's not as widespread yet.

Re: Can I erase sensitive data on an old hard drive with Neodymium Magnets?

#107

Post by KozmoNau7 »

FooHentai wrote: post #30
mark-r wrote: post #23

Is it really necessary to overwrite the data multiple times to erase it? With the densities provided by today's hard drives, the techniques you used to be able to use to get partially erased data are routinely used by the disk drive itself for normal reads.

What's your threat model? Data must not be recoverable for at least the next X years, or data must not be recoverable within any future time frame, no exceptions? For the former, you're absolutely right. For the latter, multiple-pass overwrite provides greater assurance than single pass. Following that up with physical destruction of the platters provides further assurance.

Why even bother with overwriting the data if you're just going to physically destroy the platters and/or heat them beyond their curie point anyway?

Re: Can I erase sensitive data on an old hard drive with Neodymium Magnets?

#108

Post by harshreality »

quickben wrote: post #92
harshreality wrote: post #90

Earlier quoted context omitted.

So what you're saying is that nobody can hot swap drives in a NAS without destroying neighboring drives? I don't buy that either.

No, what he is saying, is that moving magnetic field, induces current , and can mess up the cheap power supply and/or other components, which can then mess up the drives. In a server, the power supply is on the other end of the chasis. In a laptop, it's a lot closer to the internals. > I don't buy that either. Theory: https://en.wikipedia.org/wiki/Electromagnetic_induction The forward model: https://www.youtube.com/w…

Nobody is suggesting that electromagnetic theory is false. The question is whether there's really a danger from HDD magnets in motion relative to nearby electronics or HDD platters.

- HDDs often live right next to each other (separation of roughly 1cm, front to back).

- Power supplies and their induction coils are right next to the drives in some cases, including for instance consumer grade NAS boxes.

- HDDs tend to have a coil of wire, too.

If HDD magnets overwriting nearby HDD data was a thing, it would be happening all the time.

If HDD magnets in motion in certain orientations were inducing damaging currents in nearby HDDs or in nearby power supplies which then damaged connected components, that would be happening less often but still all the time. Not all chassis designs have power supplies at the opposite end as the disks, and some applications like consumer NAS boxes have them in close proximity to each other.

Re: Can I erase sensitive data on an old hard drive with Neodymium Magnets?

#109

Post by AnIdiotOnTheNet »

golem14 wrote: post #91
AnIdiotOnTheNet wrote: post #54

Earlier quoted context omitted.

Right? What are the people in this thread doing that they're worried someone would take the time to employ theoretical, if not entirely hypothetical, recovery methods against a zeroed disk?

Zeroing out a 4tb drive takes some time. Sometimes you might be in a hurry ;)

That's fair, but that doesn't explain the people talking about 10 pass overwrite routines and other such nonsense.

Re: Can I erase sensitive data on an old hard drive with Neodymium Magnets?

#110

Post by EvanAnderson »

joering2 wrote: post #55
EvanAnderson wrote: post #17

Here's my anecdote: In 2006, while sitting at my desk playing a video on the hard disk drive of my Thinkpad T22, I held a single neodymium magnet (harvested from an old hard disk drive) about 6 inches from the left side of the unit (where the ~40GB-ish Travelstar 2.5" PATA disk was located). The video froze, Windows XP blue-screened, and the hard disk drive started emitting a ~10Khz whine. I jerked my hand away from…

Out of curiosity, what was the brand and model of that HDD? Would like to dive deeper into its construction, etc.

It was a Travelstar (I believe still under IBM ownership at that time) 2.5" PATA drive. I don't have the exact model handy. I took a look in my "dead disks" shoebox and I don't believe I even have the drive anymore. If I run across it I'll drop a comment on here.
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