Usually my process is very… hammer and drill related - but I have a family member who is interested in taking my latest batch of hard drives after I upgraded.
What are the best (linux) tools for the process? I’d like to run some tests to make sure they’re good first and also do a full zero out of any data. (Used to be a raid if that matters)
Edit: Thanks all, process is officially started, will probably run for quite a while. Appreciate the advice!
So I run encrypted drives except for the odd thing where it would be a pain in the anoos, but what would… drive… someone to physically destroy the drives?
Literally the only thing I can think of is having massive amounts of illegal data but what would that even be.
Physically destroying drives is standard operating procedure. Big data centres and data brokers literally have a giant industrial shredder in the basement which shred and pulverise all obsolete hardware.
Anyone with any sort of fiduciary or legal duty to keep any data safe would also need to destroy data storage - think Lawyers, Doctors with their own clinics, Journalists, Police Officers etc. Now even people in finance need to worry about their data, because even the most inane shit like call logs from a mid to high level banker can be sold for a fuckton of money.
Or it could be plans for 9-11 part deux electric boogaloo, can’t tell.
Just FYI: the often-cited NIST-800 standard no longer recommends/requires more than a single pass of a fixed pattern to clear magnetic media. See https://nvlpubs.nist.gov/nistpubs/specialpublications/nist.sp.800-88r1.pdf for the full text. In Appendix A "Guidelines for Media Sanitation" it states:
Overwrite media by using organizationally approved software and perform verification on the
overwritten data. The Clear pattern should be at least a single write pass with a fixed data value,
such as all zeros. Multiple write passes or more complex values may optionally be used.
This is the standard that pretty much birthed the "multiple passes" idea, but modern HDD technology has made that essentially unnecessary (unless you are combating nation-state-sponsored attackers, in which case you should be physically destroying anything anyway, preferably using some high-heat method).
it's not much use now, but to basically avoid the entire issue just use whole disk encryption the next time. Then it's basically pre-wiped as soon as you "lose" the encryption key. Then simply deleting the partition table will present the disk as empty and there's no chance of recovering any prior content.
Does one have to supply the password at each boot with what you are describing - this sounds like the password is somewhere in the partition table. If so what do I google to learn more?
There's many different ways with different performance tradeoffs. for example for my Homeland server I've set it up that I have to enter it every boot, which isn't often. But I've also set it up to run a ssh server so I can enter it remotely.
On my work laptop I simply have to enter it on each boot, but it mostly just goes into suspend.
One could also have the key on a usb stick (or better use a yubikey) and unplug that whenever is reasonable.
There are many ways to setups full disk encryption on Linux, but the most common all involve LUKS. Providing a password at mount (during boot, for a root partition or perhaps later for a “data” volume) is a but more secure and more frequently done, but you can also use things like smart cards (like a Yubikey) or a keyfile (basically a file as the password rather than typed in) to decrypt.
So, to actually answer your question, if you dont want to type passwords and are okay with the security implementations of storing the key with/near the system, putting a keyfile on removable storage that normally stays plugged in but can be removed to secure your disks is a common compromise. Here’s an approachable article about it.
I have been researching the same question a few days ago and am currently running > badblocks -b 4096 -c 8 -svw /dev/sdaon my old NAS drive. It makes a few passes writing the disk full of 0xaa and 0x55 and then reading it back. I have my disk in a USB2.0 SATA adapter on a raspberry pi 3 and it’s currently at 70% of pass #2 after 100 hours, so it sure is slow, but I don’t mind.
While this wouldn’t work for you now, something to think about is encrypting new drives going forward so that you don’t have to worry about erasing/zeroing them, just toss the encryption key and your good to go.
‘dd’ works, but I prefer ‘shred’. It does a DoD multi-pass shred by default, so I usually use ‘shred -vn1z /dev/(drive)’. That gives output, does a one-pass random write followed by one-pass zero of the disk. More than that just wastes time, and this kinda thing takes hours on large spinners. I also use ‘smartmontools’ to run SMART tests against my drives regularly to check their health.
Just a heads up that's not a thing anymore (since 2006 when the 1995 revision was superseded), except that you have to physically destroy it or whatever the CSA's policy that owns it says to do. Generally the direction for an HDD would be, if available, use a degaussing rod and then regardless, you must shred it in an approved HDD shredder (a physical shredder) or incinerate it. For an SSD, it would be to incinerate it.
Now 5220.22-M (the 1995 version) that most commercial and some not-so-commercial software referenced as the "DOD Standard" doesn't even exist anymore. It is now 32 CFR Part 117 of Title 32 and with respect to sanitization is §117.18 (b)(2).
Shred is what I used when destroying a bunch of old drives.
Then I disassbled them to pull out the magnets and platters (because they’re shiny and cool). A couple had torx screws that I didn’t have the right end for so I ran a hdd magnet over the surface and scratched them with a screwdriver.
I have an inch-high stack of platters now. Kind of interesting to see how their thickness has changed over the years, including a color change in there somewhere. Keep thinking I should bury them in epoxy on some table top.
For extra fun, you ca melt the casings and cast interesting shapes. I only wish I were smart enough to repurpose the spindle motors.
Just doing a single pass all the same like zeroes, often still leaves the original data recoverable. Doing passes of random data and then zeroing it lowers the chance that the original data can be recovered.
The “can” in can be recovered means “if a state sponsored attacker thinks that you have nuclear secrets on that drive, they can spend millions and recover data by manually analyzing the magnetic flux in a clean room lab” not “you can recover it by running this program”
Like u/MrMcGasion said, zeroing makes it easier to recover original data. Data storage and signal processing is pretty much a game of threshold values. From digital world you might see 0 or 1, but in reality it’s a charge on a certain scale, lets assume 0 to 100%. Anything above 60% would be considered 1 and anything below 45% a 0. Or something like that.
When you do zero the drive, that means drive will reduce charge enough to pass the lower limit, but it will not be 0 on any account. With custom firmware or special tools it is possible to configure this threshold and all of the sudden it is as if your data was never removed. Add to this situation existence of checksums and total removal of data becomes a real challenge. Hence why all these tools do more than one operation to make sure data is really zeroed or removed.
For this reason random data is better approach is much better than zeroing because random data alters each block differently instead of just reducing charge by a fixed amount, as it is with zeroing. Additional safety is achieved by multiple random data writes.
All of this plays a role only on magnetic storage, that is to say HDDs. SSD is a completely different beast and wiping SSD can lead to reduced lifespan of the drive without actually achieving the desired result. SSDs have write distribution algorithms which make sure each of the blocks are equally used. So while your computer thinks it’s writing something at the beginning of the drive, in reality that block can be anywhere on the device and address is just internally translated to real one.
I’ve been using Shred to wipe things at work. I give it seven passes of random, then a pass of zeros. Probably overkill, but everything is going to surplus auctions and some of the data is sensitive.
conv=fsync: basically does the equivalent of running “sync” after the command, makes sure all the kernel buffers have actually written out and are on the device. This causes the command to “hang” near the end depending on how much RAM is installed on the computer. It’s not actually hanging it’s just finishing writing out the data that’s still cached in RAM. This can take a while depending on drive speed and quantity of system RAM.
bs=4M sets the block size to something high enough you’re not CPU bottlenecked. Not particularly important exactly what the value is, 4M is a good sane default for most things including this full disk operation.
edit: one pass of zeros is enough to protect against all trivial data recovery techniques. If your threat model includes three letter agencies the hammer and drill bit technique is 👍
Thanks! I’ve used dd for things like recovering/cloning drives but it makes complete sense I can wipe it too. Thanks for the progress trick too, it was always just a blank cursor to me when I ran it before!
I recommend using a different set of flags so you can avoid the buffering problem @thenumbersmason mentions.
This next example prevents all of your ram getting uselessly filled up during the wipe (which causes other programs to run slower whenever they need more mem, I notice my web browser lags as a result), allows the progress to actually be accurate (disk write speed instead of RAM write speed) and prevents the horrible hang at the end.
“oflag” means output flag (to do with of=/dev/somedisk). “sync” means sync after every block. I’ve chosen 128M blocks as an arbitrary number, below a certain amount it gets slower (and potentially causes more write cycles on the individual flash cells) but 128MB should be massively more than that and perfectly safe. Bigger numbers will hog more ram to no advantage (and may return the problems we’re trying to avoid).
If it’s an SSD then I issue TRIM commands after this (“blkdiscard” command), this makes the drive look like zeroes without actually having to write the whole drive again with another dd command.
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