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Da_Nuke
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 Posted: Fri Mar 09, 2012 5:37 am Post subject: My disk erasing procedures -- do you think that's enough? |
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OK, so, as a network engineer who has studied topics on encryption and security, I know damn well how easy it is to retrieve supposedly erased stuff from an HD like a highly compromising legal declaration, or let's be honest, that folder of lewd Japanese drawings of fictional girls, so in order to avoid this I religiously encrypt absolutely everything I wouldn't like others to see and I erase my hard drives' contents every week. The only thing that keeps me from using full disk encryption is the fact that Truecrypt doesn't supports dual-boot systems, and I require Windows because I'm a huge fan of Touhou Project in my experience it's been rather hard to get Touhou games running on Debian Wheezy (I've only managed to run EOSD, Imperishable Night and Mountain of Faith).
The erasure process goes like this:
- Weekly erasing: Just a quick pass of Windows's Eraser utility, then I fill my Linux partition with /dev/urandom noise and then I run sfill and sswap to clear anything that remained as well as my swap partition.
- Bi-weekly erasing: Create a Truecrypt volume spanning all the partition's free space, run one pass of Eraser on them, then /dev/urandom, sfill and sswap on my Linux partitions.
- Monthly erasing: Eraser on Windows is run with Bruce Schneier's 7-pass method, Linux erasure is done with 7 passes of /dev/urandom as well. This is finished with one final pass of encrypted /dev/urandom on everything.
- Annual erasing: Uses 35-pass Gutmann instead of Schneier's 7-pass. This is followed with 3 passes of encrypted /dev/urandom on all my drives' free space.
- Destroying a drive with DBAN and restoring its contents with Clonezilla is out of the question because it would be extremely lengthy and I don't have that much time to spare.
Thing is, because I spend very little time at home these erasing cycles have been starting to become very time-consuming, so now I'm forced to cut back on my disk cleaning efforts. That, and I'm also starting to become far more careful to not save plaintext on my computer in the first place (I always open a private window on Chromium prior to browsing 4chan or Danbooru).
So, basically, the question is: are these disk cleaning procedures enough? |
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BoneKracker
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Joined: 14 Mar 2006
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| Posted: Fri Mar 09, 2012 7:23 am Post subject: |
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No. Stop deceiving yourself with all this flailing. You are still not protected. There is only one way you can be adequately protected, and that is to operate entirely in RAM without a hard disk altogether (or from a read-only disk). This is what you need:
http://opensource.dyc.edu/tinhat
Keep in mind, however, that data can actually be recovered from RAM chips for a while even after a computer has been shut down, and this can be used to recover encryption keys for any disk encryption anyway. So to be safe, you must power off the system and then sit there to maintain absolute physical control over the RAM for at least a 5-minute power dissipation interval (10 minutes to be super, super safe).
https://citp.princeton.edu/research/memory/
For variable persistent data (including things like /var /home and so on), you should use an encrypted removable flash stick (i.e. jump drive, thumb drive, etc.). If you yourself fall into their clutches, you can then swallow it or shove it deep (deeper than a tall man's fingers) in your ass.
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Last edited by BoneKracker on Fri Mar 09, 2012 7:25 am; edited 1 time in total |
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Muso
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Joined: 22 Oct 2002
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Location: The Holy city of Honolulu
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| Posted: Fri Mar 09, 2012 7:24 am Post subject: |
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Bleach + Sledgehammer = Erased.
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aidanjt
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| Posted: Fri Mar 09, 2012 11:28 am Post subject: |
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If you're that paranoid, then just do full-disk encryption ffs. And run windows in a VM (VMware 8 actually produces very usable 3D accel).
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| juniper wrote: | | you experience political reality dilation when travelling at american political speeds. it's in einstein's formulas. it's not their fault. |
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cach0rr0
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Location: Houston, Republic of Texas
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| Posted: Fri Mar 09, 2012 11:43 am Post subject: |
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my setup for my boxen that require windows:
-grub and /boot on unencrypted usb stick
-crypt keys on separate usb stick, that's really a micro-sd adapter. I can swallow a microsd card in a pinch.
-sda1 == windows, only encrypted containers via truecrypt
-sda2-* == gentoo, dmcrypt=>lvm volumes, everything encrypted
more than sufficient, and functional.
your weekly overwrites are absurdly excessive. seriously. I'm the guy talking about swallowing a micro-sd card, and I'm saying your weekly overwrites are absurd. |
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username234
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| Posted: Fri Mar 09, 2012 12:23 pm Post subject: |
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| Peter Gutmann wrote: | | 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. |
Source: http://www.cs.auckland.ac.nz/~pgut001/pubs/secure_del.html
The easiest way to securely erase a hard disk is to ask the drive controller to do it. This can be done using hdparm. See http://tinyapps.org/docs/wipe_drives_hdparm.html for details.
As for your current setup, it's clearly overkill. I'd suggest you actually spend the time researching exactly what it takes to successfully clear a hard disk instead of running just about every erasure tool you can find. This is especially true for SSDs as your current technique would just wear them out faster than necessary.
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Creating usernames when you're
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aidanjt
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| Posted: Fri Mar 09, 2012 12:37 pm Post subject: |
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Yeah I tend to just dd /dev/zero over spinners and use hdparm --security-erase on ssds. That's ample to make the data entirely inaccessible to pretty much anyone (certainly for SSDs, since every block is reset to all zeroes). The ATA erase command can be done on spinners too but it isn't any faster than dd.
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| juniper wrote: | | you experience political reality dilation when travelling at american political speeds. it's in einstein's formulas. it's not their fault. |
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energyman76b
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| Posted: Fri Mar 09, 2012 3:34 pm Post subject: |
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dd if/dev/zero is even save enough for all the paranoids out there. Doing more does not increase your security.
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Libertardian denial of reality is wholly unimpressive and unconvincing, and simply serves to demonstrate what a bunch of delusional fools they all are.
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danomac
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Joined: 06 Nov 2004
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| Posted: Fri Mar 09, 2012 4:13 pm Post subject: |
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For the drives at work, I take the drives apart, remove the platters, and use my belt sander with a 40-grit sandpaper on them. Doubtful that'll be recoverable.  |
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aidanjt
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| Posted: Fri Mar 09, 2012 4:18 pm Post subject: |
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| danomac wrote: | | For the drives at work, I take the drives apart, remove the platters, and use my belt sander with a 40-grit sandpaper on them. Doubtful that'll be recoverable. |
Noob.. real paranoid loons bombard the platters with positrons until they're completely disintegrated.
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| juniper wrote: | | you experience political reality dilation when travelling at american political speeds. it's in einstein's formulas. it's not their fault. |
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nomilieu
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Joined: 22 Nov 2011
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| Posted: Fri Mar 09, 2012 4:32 pm Post subject: |
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| energyman76b wrote: | | dd if/dev/zero is even save enough for all the paranoids out there. Doing more does not increase your security. |
I did exactly this to dozens of hard drives recently, which is AFAICT in compliance with state law.
Unfortunately, there is a campus rule (which may be written somewhere, but not publicly, and I wasn't told) that they must be physically destroyed anyways.
So, instead of reselling perfectly good used state computers to regain some cash, we're going to flush it down the toilet and sell worthless scrap*, especially stupid since there's nothing sensitive on the drives to begin with.
*Average Joe will buy a used computer for a fair price, but not if there's no hard drive. |
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jdmulloy
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Joined: 24 Dec 2004
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| Posted: Fri Mar 09, 2012 5:31 pm Post subject: |
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What do you mean Truecrypt doesn't support dual boot? I'm 0pretty sure you can just encrypt the Windows partition and use dmcrypt for the Linux partition. I use dmcrypt on my home workstation and laptop. I don't bother encrypting the Windows 7 partition on my workstation since it's pretty much just for gaming. I'd suggest just using dmcrypt on Linux and not doing anything sensitive on Windows. Even if you did use encryption on Windows you're still susceptible to viruses so again I would recommend not ever doing anything sensitive on Windows. Also if you have a higher end version of Windows Vista/7 you can use bitlocker to encrypt the drive. Of course this does mean you have to trust that Microsoft didn't screw up the implementation or provide a backdoor for governments.
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sts
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Joined: 02 Jul 2007
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| Posted: Fri Mar 09, 2012 8:51 pm Post subject: |
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Yeah, what everyone else said:
1) dm-crypt is the defacto FDE for linux.
2) All you need to irrevocably erase data is to overwrite it (such as with /dev/zero) at the device level. Data recovery relies on filesystem metadata and filesystem laziness (not overwriting deleted files). The Gutmann method was developed for outdated technology (MFM/RLL encoded disks), all you're doing is reducing the life of your hard drive. Also the "Secure Erase" standard is supported by hdparm if you'd like to use that.
[If you're using SSD, things are a bit more tricky. Might want to use FDE from the start since full erasure is hard to guarantee.]
Disk encryption is good protection against a stolen hard drive but you can't really do much for protection against the gov (or any sufficiently motivated organization with vast resources). If you're doing something illegal or you've otherwise captured their attention they'll just find other ways to convict (ISP records, email, server logs, data leakage, arresting you while you are using your laptop and everything is open, etc) or compel you to decrypt the drive. |
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sts
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Joined: 02 Jul 2007
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| Posted: Fri Mar 09, 2012 9:03 pm Post subject: |
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| nomilieu wrote: | | energyman76b wrote: | | dd if/dev/zero is even save enough for all the paranoids out there. Doing more does not increase your security. |
I did exactly this to dozens of hard drives recently, which is AFAICT in compliance with state law.
Unfortunately, there is a campus rule (which may be written somewhere, but not publicly, and I wasn't told) that they must be physically destroyed anyways.
So, instead of reselling perfectly good used state computers to regain some cash, we're going to flush it down the toilet and sell worthless scrap*, especially stupid since there's nothing sensitive on the drives to begin with.
*Average Joe will buy a used computer for a fair price, but not if there's no hard drive. |
This is a good policy to cover their ass from liability. Certain types of campus records are considered sensitive private information (grading, social security #s, financial and loan records, etc). You can't tell if a hard drive was properly formatted by looking at it, so they just require you to format it and then destroy it to make sure the data doesn't get exposed.
Governments typically require this type of disposal, too. There's also a very remote possibility they'll be able to recover usable data from a portion of the hard drive that is not accessible through your operating system. (bad sectors, disk caches, etc.) |
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BoneKracker
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| Posted: Fri Mar 09, 2012 9:44 pm Post subject: |
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| aidanjt wrote: | | danomac wrote: | | For the drives at work, I take the drives apart, remove the platters, and use my belt sander with a 40-grit sandpaper on them. Doubtful that'll be recoverable. |
Noob.. real paranoid loons bombard the platters with positrons until they're completely disintegrated. |
And then, when they've turned to dust, shove it deep (more than the length of a tall man's fingers) up your ass. It's the only way to be sure.
_________________
Oldthinkers unbellyfeel INGSOC.
-- Headline of a document on Winston Smith's terminal in his cubicle at the Ministry of Truth, seen briefly in the background in one scene of the movie rendition of Nineteen Eighty-Four. |
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nomilieu
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| Posted: Fri Mar 09, 2012 10:19 pm Post subject: |
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| sts wrote: | | nomilieu wrote: | | energyman76b wrote: | | dd if/dev/zero is even save enough for all the paranoids out there. Doing more does not increase your security. |
I did exactly this to dozens of hard drives recently, which is AFAICT in compliance with state law.
Unfortunately, there is a campus rule (which may be written somewhere, but not publicly, and I wasn't told) that they must be physically destroyed anyways.
So, instead of reselling perfectly good used state computers to regain some cash, we're going to flush it down the toilet and sell worthless scrap*, especially stupid since there's nothing sensitive on the drives to begin with.
*Average Joe will buy a used computer for a fair price, but not if there's no hard drive. |
This is a good policy to cover their ass from liability. Certain types of campus records are considered sensitive private information (grading, social security #s, financial and loan records, etc). You can't tell if a hard drive was properly formatted by looking at it, so they just require you to format it and then destroy it to make sure the data doesn't get exposed.
Governments typically require this type of disposal, too. There's also a very remote possibility they'll be able to recover usable data from a portion of the hard drive that is not accessible through your operating system. (bad sectors, disk caches, etc.) |
Oh yeah, I get it; I just wish they told me first. These were mostly student lab machines or library worker machines, and no one is supposed to be storing anything at all on them, let alone sensitive stuff. There is a state law here giving the acceptable methods for erasing hard drives of obsolete equipment before it goes to sale, so I thought complying with that law would be enough. (The law exists because some state machines were sold about a decade ago with lots of social security numbers and such saved on the hard drives. That wasn't due to crappy erasure methods though; it was due to some idiots not even bothering to erase them at all.)
As for bad sectors and such, I did make sure to toss into a junk (i.e. destroy) pile any drive that gave me a write error while dd'ing them.
There were a few of them. Some of these drives were 15 and even 20 years old. |
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charly
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| Posted: Fri Mar 09, 2012 10:39 pm Post subject: |
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PEBKAC
(all security, that is)
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charly
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| Posted: Fri Mar 09, 2012 10:44 pm Post subject: |
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| danomac wrote: | | For the drives at work, I take the drives apart, remove the platters, and use my belt sander with a 40-grit sandpaper on them. Doubtful that'll be recoverable. |
actually, as long as there is a magnetic field around the disk then machines can build up partial info from the magnetic remnants
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sts
Tux's lil' helper
Joined: 02 Jul 2007
Posts: 97
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| Posted: Fri Mar 09, 2012 10:46 pm Post subject: |
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| charly wrote: | | danomac wrote: | | For the drives at work, I take the drives apart, remove the platters, and use my belt sander with a 40-grit sandpaper on them. Doubtful that'll be recoverable. |
actually, as long as there is a magnetic field around the disk then machines can build up partial info from the magnetic remnants |
That type of stuff is essentially urban legend. |
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charly
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Joined: 05 Apr 2011
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| Posted: Fri Mar 09, 2012 10:59 pm Post subject: |
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| sts wrote: | | charly wrote: | | danomac wrote: | | For the drives at work, I take the drives apart, remove the platters, and use my belt sander with a 40-grit sandpaper on them. Doubtful that'll be recoverable. |
actually, as long as there is a magnetic field around the disk then machines can build up partial info from the magnetic remnants |
That type of stuff is essentially urban legend. |
the government agencies have machines to do it, they are the size of cars
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jdmulloy
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Joined: 24 Dec 2004
Posts: 139
Location: Massachusetts, USA
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| Posted: Sat Mar 10, 2012 12:23 am Post subject: |
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| sts wrote: | Yeah, what everyone else said:
1) dm-crypt is the defacto FDE for linux.
2) All you need to irrevocably erase data is to overwrite it (such as with /dev/zero) at the device level. Data recovery relies on filesystem metadata and filesystem laziness (not overwriting deleted files). The Gutmann method was developed for outdated technology (MFM/RLL encoded disks), all you're doing is reducing the life of your hard drive. Also the "Secure Erase" standard is supported by hdparm if you'd like to use that.
[If you're using SSD, things are a bit more tricky. Might want to use FDE from the start since full erasure is hard to guarantee.]
Disk encryption is good protection against a stolen hard drive but you can't really do much for protection against the gov (or any sufficiently motivated organization with vast resources). If you're doing something illegal or you've otherwise captured their attention they'll just find other ways to convict (ISP records, email, server logs, data leakage, arresting you while you are using your laptop and everything is open, etc) or compel you to decrypt the drive. |
Actually Secure Erase on SSDs is pretty good and it takes about 30 seconds. It just resets ALL the flash blocks to their default state. It's commonly used to restore the performance of a well used drive.
Of course if you don't use a good unique password it's no good anyways. If it's the same password you use on a site that doesn't properly hash passwords then the government can get the password from the site and try it on your PC. Also don't share your password, ever, with anyone.
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BoneKracker
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| Posted: Sat Mar 10, 2012 5:25 am Post subject: |
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And, if you do write it down, be sure to shove it deep in your ass.
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Oldthinkers unbellyfeel INGSOC.
-- Headline of a document on Winston Smith's terminal in his cubicle at the Ministry of Truth, seen briefly in the background in one scene of the movie rendition of Nineteen Eighty-Four. |
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aidanjt
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| Posted: Sat Mar 10, 2012 5:52 am Post subject: |
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| BoneKracker wrote: | | aidanjt wrote: | | Noob.. real paranoid loons bombard the platters with positrons until they're completely disintegrated. |
And then, when they've turned to dust, shove it deep (more than the length of a tall man's fingers) up your ass. It's the only way to be sure. |
Yeah, should probably attach that with a warning "WARNING: This positron-disintegrated platter dust may contain a significant quantities of alpha-decaying unstable isotopes and shoving it up your rectum may lead to ass cancer". Just for legal purposes.
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| juniper wrote: | | you experience political reality dilation when travelling at american political speeds. it's in einstein's formulas. it's not their fault. |
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cach0rr0
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| Posted: Sat Mar 10, 2012 7:45 am Post subject: |
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by the by, is dmcrypt on SSD's still a no-go?
reorganizing my travel gear, gong to snag a new Thinkpad
if dmcrypt is still a no-go with SSD, I buy one with a 7200RPM disk that's big enough for my media
if dmcrypt and SSD's can play nicely with each other now (i.e. is the built-in wear-leveling sufficient? is a periodic wiper.sh sufficient?), I snag one with an SSD, and bring along a small external drive in my kit |
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aidanjt
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| Posted: Sat Mar 10, 2012 7:49 am Post subject: |
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The only real big problem with dm-crypt on SSD is that TRIM is disabled, and performance gets hit by the random noise already written to all cells. It wont significantly shorten the lifespan of the disk, but performance will be nowhere near the same as an unencrypted disk.
Maybe you'd be more interested in one of the hybrid drives which pretty much use flash as a huge buffer.
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| juniper wrote: | | you experience political reality dilation when travelling at american political speeds. it's in einstein's formulas. it's not their fault. |
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