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Data Still Left on Storage Devices for Sale
cluedweasel writes "According to a BBC story many people are still putting up their old PC's and storage devices for sale without taking basic precautions to ensure that confidential data is erased. The suggestion at the end of the story is to get a professional forensics firm to wipe your data or just destroy the item in question. With the low price of storage devices, the latter is probably preferable."
Darik's Boot and Nuke. Cheap, efficient, portable. Worst thing that happened using it was cleaning a PC so old its CD-ROM drivers weren't in firmware, so I had to download a boot disk off the net to reinstall them.
"Made up/misattributed quote that makes me look smart. I am on
...with something like Darik's Boot & Nuke
I seriously doubt that any magnet you can get your hands on would erase anything from a hard drive platter. Even bulk tape deguassers from five years ago won't do shit on a modern drive. It takes some seriously strong fields to erase a platter.
However, sticking a decently strong household or lab magnet against the drive housing may tense parts of the delicate mechanism inside, causing the bearing to go south or the actuator arm to cease working. It's still probably possible to pull the platters and remount them in a new housing (if the platters weren't too damaged by whatever mechanical failure you induce), and there are a few outfits that can do it for ~$3000 per drive.
Now, get real: Want to know the BIGGEST, best-kept secret in data forensics? The most effective way to forever put your data beyond the reach of cops and courts is:
dd if=/dev/zero of=/dev/hda
That's right, just a single-pass overwrite with zeros will do. Everything else you hear is either 8+ years out of date, or uninformed bullshit, or a scare story.
I raised this issue with the manufacturer of my USB key, after it ceased to communicate. I was offered a brand-new one upon receipt of the old one, but had no way to clear the data (a CVS tree of our product). The tech said any obvious, physical damage (i.e smashing with a hammer) would void the replacement guarantee.
Apparently, a few seconds in the microwave does not qualify as obvious, physical damage.
Now, get real: Want to know the BIGGEST, best-kept secret in data forensics? The most effective way to forever put your data beyond the reach of cops and courts is:
dd if=/dev/zero of=/dev/hda
/dev/urandom is a better source... With zero, analog analysis can be used to determine the drive's prior contents. Of course, if somebody is willing to do that to recover data, they already have your house bugged...
That's right, just a single-pass overwrite with zeros will do. Everything else you hear is either 8+ years out of date, or uninformed bullshit, or a scare story.
May as well do a second pass with /dev/random, though it's not like the cops are going to send your drive in for forensic recovery unless you're a big fish.
"We returned the General to El Salvador, or maybe Guatemala, it's difficult to tell from 10,000 feet"
I was wondering the other day what kind of shielding a drive has to keep its own magnets from wiping itself...
From what I saw in defect drives I opened, none at all, just some centimeters distance. The "strong magnet" meme is an urban m"yth. You need far stronger static magnetic fields to damage a drive without opening it than you can buy.
In addition, if you succeeded, it would likely void the warranty anyway, so why not be sure and just decline the warranty or use an encrypted filesystem in the first place?
Most ACs are not even worth the keystrokes to insult them. Be generically insulted by this and ignored otherwise.
or just destroy the item in question
Nooo!!!
I worked as the technology re-use manager at a nonprofit organization whose mission was to get donated goodies, including computers (my responsibility), to small local charitable organizations. Our warehouse had pallet upon pallet of donated computers whose hard drives were removed as part of corporate donors' policies regarding data safety. Did we get those computers to community centers, adult education programs, inner city kids, etc? Heck no, we had to send them to the metal recycler for 2 cents per pound. Sure, per-storage unit hard drives are cheap but to get enough for a couple of hundred computers is a major expense. And yes, we applied to Maxtor, Seagate, IBM, HP and a couple of others to try to get them to donate hard drives but no dice.
The late-middle aged lady who wants to type and print the church newsletter has ABSOLUTELY no use for a computer without a hard drive and even less of an idea how to install one even if she did have budget to get one. Get a commercially available eraser program; there are plenty of titles and methods. Said church lady has NO IDEA how to extract prior data from a drive that was just plain formatted and a fresh Windows installation put on.
Strong magnets (as strong as you're likely to have at home anyways) will erase (ruin) floppy media just fine. And cassette tape media. And probably 8 tracks. I don't know what they'll do to QIC-150, 4 mm or 8 mm media. But they won't erase DLT media, and won't erase modern hard drives, probably not even if you put it right next to the platter itself.
(Now, opening the drive up and scraping the magnet over the drum, physically damaging it, that may be effective. But a non-magnetic wire brush would work as well.)
Personally, I erase my media with some variation of this --
and let that go until it's done. Repeat if you're extra paranoid. Sure, there may be some data left in sectors that have been re-allocated by the firmware. Sure, the NSA might be able to recontruct my data bit by bit with microscopes. But if I'm really worried about that, I'm not going to sell my disk -- I'm going to physically destroy it.As for warranty repair, that's a tough call. If the dd can't be done, the odds are good that the company can recover almost everything on the disk. You'll have to consider the pros (you get a new disk! free!) vs. the cons (they might be able to recover all of your data.)
To give an example, suppose a part of your drive had this pattern written on it --
and you overwrote that with 0s. So you'd expect to seeand you would, if you read the drive in the normal way. However, underneath the covers, the data on the drive would really look more like this --the exact values are just guesses, but there is a pattern here -- if a bit used to be 0, it's very close to 0 now. If the bit used to be 1, it's still close to 0 now, but a good deal further than if it was a 0.With some different firmware, one could read most of the data that was on a drive that had been erased like this.
This is why people 1) write random or semi-random patterns to the disk to erase it, and 2) do it more than once.
Still, writing 0's just once to the entire disk will stop 99% of people who might read your disk. Writing random patterns several times will probably stop even the NSA, but if they want you bad enough, they'll stick probes into your brain and extract it that way :)
The big paper that started all this is here:
_ del.html
http://www.cs.auckland.ac.nz/~pgut001/pubs/secure
(sorry if the link gets tangled). The author is Peter Gutmann. The paper you see on that link is actually an updated version of the original, which was published at USENIX '96, minus the "epilogue" section at the end. That's the critical part, where Gutmann basically backs off all the important conclusions about hard drive data recovery. He's still pretty optimistic in the epilogue (he talks about recovering one or two previous write passes of data), but you have to notice that he doesn't support himself, there, and the original citations don't support him, either.
Not to speak ill of Gutmann--he's done a lot of great work in UNIX security over the years, and he's a stand-out researcher. But he doesn't prove what he's saying.
Hopefully, the Gutmann terminology will be enough to get you started if you want to research the issue further. I used to have a couple dozen pages of cites and summaries on the issue, but I lost most of it when I left my last job. It's still out there, but it took me a couple of months to do it originally.
Magnets just don't work for erasing data. One or two passes with good pseudo-random data are all that is needed, and even the NSA would be reliably stumped with 5 or more on modern disks. Writing constant patterns is somwhat less effective because the encoding to analog on the disc prevents long strings of highs or lows being written and because any residual field from previous writes can potentially be seperated from the constant overwrite pattern.
;|
You don't need to worry about this level of security if your threat model is phishers and the like. The people selling hard drives would like you to be so paranoid you won't let others make use of your old hardware, but there is no real need for that. If someone with the resources to go over your HDD nanometer by nanometer with SQuIDs wants your data, they'll first try a sneakier, more effective way than buying your old disks.
For quick destruction of encrypted data, assuming the encryption-block size is several times the disk-block size, overwriting just one of the disk blocks for each encryption block will effectively make the data unrecoverable. Similarly, if you use an encrypted file of long, secure keys to access your other encrypted data, once that file is destroyed, everything else is effectively gone until the encryption can be brute-forced a few decades down the line.
But for sensitive data that may need to be quickly destroyed, you're better off using CD or DVD media. Five seconds in the microwave followed by a quick couple of rubs with a piece of sandpaper to remove the flakes will do more than just about anything you could do to an HDD in a similar amount of time. This also gives you an excuse to get a really fat UPS and to have your microwave on your desk. Of course you still need to find a way to get the time needed to destroy the data when your door is being broken down or if your machine is tampered with when you are away - left as an exercise for the reader.
"Is life so dear, or peace so sweet, as to be purchased at the price of chains and slavery?" - Patrick Henry