5 ms·

Secure delete with rm on OS X

24 points by mustpax 16y ago

Groxx 16y ago
Know what's easier? Right click the trash bin, and hold Command. You'll see "Secure Empty Trash". You can also do the rm -P from the trash bin, which I wish they allowed you to do under normal circumstances. (dterm makes this easy.)
- MikeCapone 16y ago
  Thanks. I knew you could hold "alt" when left-clicking on the volume control to select inputs, but I didn't know about that one. Very useful, much better than going in the Finder's preferences...
  - thought_alarm 16y ago
    For what it's worth, holding down Option/Alt will empty the Trash without confirmation. Also, from the menu you can select: Finder > Secure Empty Trash You can even give it a keyboard shortcut, if you like. Or, as you mentioned, there's an option to always securely empty the Trash in the Finder Preferences.
    - deleted 16y ago
      [deleted]
  - Groxx 16y ago
    Holding alt / control / command to modify a right-click menu is one of the most useful and worst UI decisions in OSX (IMO). Easily 95% of people I've encountered on Macs don't even know it exists, and when they do, they don't know how many places it exists. I really wish there were some kind of hinting to help people discover this.
santry 16y ago
Or use srm.
Maskawanian 16y ago
There is no guarantee this goes on the same sectors on the disk. I think that would only be guaranteed by a "secure delete call" to the drive's firmware. The only way I know to securely erase the empty space on the drive is a call like "cat /dev/urandom > file; rm file". This will error once the drive is full, then be deleted.
- KC8ZKF 16y ago
  Disk Utility can overwrite empty space on a device with zeros. It also has the dubious 7 and 35 pass overwrite options.
  - atomical 16y ago
    Why dubious?
    - timdoug 16y ago
      http://www.cs.auckland.ac.nz/~pgut001/pubs/secure_del.html http://www.cs.auckland.ac.nz/~pgut001/pubs/secure_del.html "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."
- mustpax 16y ago
  Interesting. But that would only be true for journaling file systems right? Or are there consumer hard disk drives that transparently journal writes a la ssd's?
deleted 16y ago
[deleted]
jrockway 16y ago
Secure delete is not reliable with modern filesystems. Just use full-disk encryption -- it's free.
- chbarts 16y ago
  > Just use full-disk encryption -- it's free. People can make bizarre assumptions without realizing it. This advice assumes that it's safe to have a disk full of noise (even if you deny it's encrypted data) in your control. That is perhaps a safe assumption under all foreseen circumstances, but it needs to be considered. Another piece of advice I see, to simply destroy all media that has ever held sensitive information, assumes that destroying media is safe, as opposed to being prima facie evidence of wrongdoing. Again, it might be safe in all circumstances under consideration, but the assumption needs to be made explicit and it needs to be considered. My point is that all these unexamined assumptions are quite unprofessional and reflect poorly on the commentators.
- wmf 16y ago
  Good thing HFS+ is not a modern filesystem. Also, I'm not sure what FDE has to do with recovering unlinked files.
  - jrockway 16y ago
    With secure delete, someone with your disk can't read deleted files. With an encrypted filesystem, they can't read the non-deleted files, either.
- newman314 16y ago
  SSDs with FDE... http://www.computerworld.com/s/article/9131684/Full_disk_encryption_comes_to_SSDs_for_mobile_devices_laptops http://www.computerworld.com/s/article/9131684/Full_disk_enc...
- coin 16y ago
  I haven't been able to find a free bootable full-disk encryption solution for the Mac. TrueCrypt is free but doesn't support bootable whole-disk encryption for the Mac. The only solution I found was PGP Whole Disk Encryption which isn't free.
Niten 16y ago
This isn't an OS X specific feature, it's a feature from the FreeBSD userland that Apple borrowed into OS X.

24 points by mustpax 16y ago

Groxx 16y ago

Know what's easier? Right click the trash bin, and hold Command. You'll see "Secure Empty Trash". You can also do the rm -P from the trash bin, which I wish they allowed you to do under normal circumstances. (dterm makes this easy.)

MikeCapone 16y ago
Thanks. I knew you could hold "alt" when left-clicking on the volume control to select inputs, but I didn't know about that one. Very useful, much better than going in the Finder's preferences...
- thought_alarm 16y ago
  For what it's worth, holding down Option/Alt will empty the Trash without confirmation. Also, from the menu you can select: Finder > Secure Empty Trash You can even give it a keyboard shortcut, if you like. Or, as you mentioned, there's an option to always securely empty the Trash in the Finder Preferences.
  - deleted 16y ago
    [deleted]
- Groxx 16y ago
  Holding alt / control / command to modify a right-click menu is one of the most useful and worst UI decisions in OSX (IMO). Easily 95% of people I've encountered on Macs don't even know it exists, and when they do, they don't know how many places it exists. I really wish there were some kind of hinting to help people discover this.

santry 16y ago

Or use srm.

Maskawanian 16y ago

There is no guarantee this goes on the same sectors on the disk. I think that would only be guaranteed by a "secure delete call" to the drive's firmware. The only way I know to securely erase the empty space on the drive is a call like "cat /dev/urandom > file; rm file". This will error once the drive is full, then be deleted.

KC8ZKF 16y ago
Disk Utility can overwrite empty space on a device with zeros. It also has the dubious 7 and 35 pass overwrite options.
- atomical 16y ago
  Why dubious?
  - timdoug 16y ago
    http://www.cs.auckland.ac.nz/~pgut001/pubs/secure_del.html http://www.cs.auckland.ac.nz/~pgut001/pubs/secure_del.html "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."
mustpax 16y ago
Interesting. But that would only be true for journaling file systems right? Or are there consumer hard disk drives that transparently journal writes a la ssd's?

deleted 16y ago

[deleted]

jrockway 16y ago

Secure delete is not reliable with modern filesystems. Just use full-disk encryption -- it's free.

chbarts 16y ago
> Just use full-disk encryption -- it's free. People can make bizarre assumptions without realizing it. This advice assumes that it's safe to have a disk full of noise (even if you deny it's encrypted data) in your control. That is perhaps a safe assumption under all foreseen circumstances, but it needs to be considered. Another piece of advice I see, to simply destroy all media that has ever held sensitive information, assumes that destroying media is safe, as opposed to being prima facie evidence of wrongdoing. Again, it might be safe in all circumstances under consideration, but the assumption needs to be made explicit and it needs to be considered. My point is that all these unexamined assumptions are quite unprofessional and reflect poorly on the commentators.
wmf 16y ago
Good thing HFS+ is not a modern filesystem. Also, I'm not sure what FDE has to do with recovering unlinked files.
- jrockway 16y ago
  With secure delete, someone with your disk can't read deleted files. With an encrypted filesystem, they can't read the non-deleted files, either.
newman314 16y ago
SSDs with FDE... http://www.computerworld.com/s/article/9131684/Full_disk_encryption_comes_to_SSDs_for_mobile_devices_laptops http://www.computerworld.com/s/article/9131684/Full_disk_enc...
coin 16y ago
I haven't been able to find a free bootable full-disk encryption solution for the Mac. TrueCrypt is free but doesn't support bootable whole-disk encryption for the Mac. The only solution I found was PGP Whole Disk Encryption which isn't free.

Niten 16y ago

This isn't an OS X specific feature, it's a feature from the FreeBSD userland that Apple borrowed into OS X.