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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?

#21

Post by cmurf »

I think magnets could compromise the read/write head, or other electronic on the drive. So why not just mulch the drive with a grinding service?

If you're looking to reuse the drive, use one of the NIST SP 800-88 Revision 1 recommendations. It lists the methods in the preferred order. Ideally the drive supports ATA crypto secure erase, where it just wipes the DEK and KEK, poof, in effect the crypto encoded form of you data can no longer be turned into plain text. You can mimic this with software FDE (Bitlocker, LUKS/dm-crypt, Filevault). Fast.

But they also say it's adequate to use the other kinds of secure erase, because other than firmware bugs/exploits it's the only way to erase sectors not assigned an LBA, e.g. sectors that once had an LBA, had data written to them, but subsequently failed overwrite and the LBA remapped to a reserve sector, leaving data on a sector that cannot be overwritten via SATA commands.

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

#22

Post by Johnny555 »

Filligree wrote: post #7
tinus_hn wrote: post #2

Even if the test would have succeeded, this is a bad idea. With a magnetic swipe card that you demagnetize so it is no longer read successfully, you may well be able to recover the information using a better reader. Depending on drive age the same may be possible using a hard drive. The best option for modern drives is still to use software to wipe the drive and if reuse is not required destroy the reading mechanism…

I won't say it's completely impossible, but modern HDD read heads are already close to our technical limit, and the signal they get is so noisy as to require extensive processing. There definitely was a period where labs could recover data this way, but I think it's passed.

Hard drives automatically remap bad sectors, so even if you overwrite 100% of the accessible data, you may still have left pieces of data in remapped sectors that weren't overwritten. If your drive supports the SECURITY ERASE feature, then it should overwrite those blocks too.

Though if you really want to sell or give your drive to someone else, the best thing to do is to use full disk encryption from the beginning, then there will be no plain text data on the drive.

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

#23

Post by mark-r »

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.

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

#24

Post by Johnny555 »

bluedino wrote: post #14
nilram wrote: post #11

A friend uses a saws-all (or something of that ilk) and cuts them in half. I'm figuring on taking my old drives to him for that treatment. I don't want to resell them and have a casual snooper recover my data, and I'm not of enough interest for anyone to piece the halves together.

I use a drill or press at work to do the same thing. Bens s drive in half or put a couple holes in the platters

Someone once suggested to me drilling a hole through the platters, then using that hole to fill the drive with salt water.

I don't know if the salt water really adds to security, but for the type of data on my drives, just drilling the hole seems like more than enough - no one is going to spend $1000 to recover my 2014 tax return from my drive since there are far easier ways to get my personal data.

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

#26

Post by keithpeter »

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…

How about whole disk encryption?

When it is time to move on, one simply forgets the passphrase and reformats the drive.

Seriously: that is what I'm doing with ssd drives. Anyone know of any issues?

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

#27

Post by amluto »

A ferromagnetic cage such as a hard drive enclosure can shield against magnetic fields pretty well. The field lines are concentrated in the enclosure and mostly avoid the inside. I would imagine you need to open the drive up to have much effect.

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

#28

Post by keithpeter »

nixpulvis wrote: post #15

This is exactly how I got out of a final project in middle school. Wiped my HDD with a Neodymium magnet right before the deadline and claimed my computer was "broken"... Of course this wasn't done for highly paranoid reasons where I needed to ensure the data was really all gone, but funny story nonetheless. People are more sympathetic when they think a computer "randomly" stopped working.

Alas, such a strategy will not work at universities local to me (UK). They specifically exclude computer malfunction as grounds for extenuating circumstances.

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

#30

Post by FooHentai »

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.

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