6 ms·

Create AES256 encrypted loop devices (.img files) under Linux

12 points by thefox 16y ago

beoba 16y ago
The link is for a perl script which is effectively a frontend for 'losetup', whose manpage describes how to create and mount images.
- thwarted 16y ago
  And I was under the impression that losetup is deprecated and LUKS/cryptsetup is the preferred method now. I used to use a script similar to the OP with losetup, but LUKS is better, at least from a UX standpoint, because you can multiple passphrases and it integrates with device mapper.
thyrsus 16y ago
The script initializes the image from /dev/zero, which means that an attacker can tell which blocks of the filesystem image are data and which are empty. Unless you really can't afford to wait the minute or so for it to finish, use /dev/urandom - or /dev/random, if you've got access to sufficient entropy (did you pay extra for a hardware random number generator?).
jerf 16y ago
A coworker of mine pointed me to EncFS, which I think is generally a better idea because you don't commit to sizing in advance: http://www.arg0.net/encfs http://www.arg0.net/encfs I have been satisfied with its performance used as the backing store for virtual machine images, though not having a dual-core may be problematic.
- jerf 16y ago
  Would have edited if I could, but I'd also point out that EncFS is immune to all the problems thyrsus cited. It only requires FUSE privs, which are generally pretty easy to give.
sp332 16y ago
I'd use AES128, it's more secure (well, so far anyway). There's a weakness in the AES256 algorithm that makes it weaker then AES128. Not weak enough that I would really be worried , but if you have the choice...
- nonUser 16y ago
  schneier has more on that: http://www.schneier.com/blog/archives/2009/07/another_new_aes.html http://www.schneier.com/blog/archives/2009/07/another_new_ae...
thyrsus 16y ago
When would one use this? When I install Fedora, it gives me the opportunity to encrypt any file system other than /boot. Since this requires you to enter the password at boot, that's good for a laptop, probably bad for a server. You need root privilege to mount a loopback file system. Either (a) you've got the root password (b) the admin has given sufficient sudo privileges or (c) you use pam_mount to mount the encrypted filesystem (probably as your home directory). Am I missing other scenarios? The trouble with the pam_mount scenario is that the key for the file system needs to be based on your login password. Either your account creation process involves telling the admin your password, or someone's built a collection of self service tools I'm unaware of. Changing your password also means building a new encrypted filesystem, which again involves giving the admin the new password, or invoking self service tools I'm unaware of. If there are other scenarios in which to use this kind of encrypted file system, I'd appreciate hearing about them.
thefox 16y ago
Thx for your feedback.
nonUser 16y ago
Why do we need a script for this task? Yet another newbie script on HN...
rlpb 16y ago
This uses cryptoloop, which SHOULD NOT BE USED IF YOU WANT STRONG SECURITY. See: http://mareichelt.de/pub/texts.cryptoloop.php http://mareichelt.de/pub/texts.cryptoloop.php You can do better with LUKS or Truecrypt. LUKS comes with most distributions. It comes with a handy wrapper called "cryptsetup" which does the setup for you.

12 points by thefox 16y ago

beoba 16y ago

The link is for a perl script which is effectively a frontend for 'losetup', whose manpage describes how to create and mount images.

thwarted 16y ago
And I was under the impression that losetup is deprecated and LUKS/cryptsetup is the preferred method now. I used to use a script similar to the OP with losetup, but LUKS is better, at least from a UX standpoint, because you can multiple passphrases and it integrates with device mapper.

thyrsus 16y ago

The script initializes the image from /dev/zero, which means that an attacker can tell which blocks of the filesystem image are data and which are empty. Unless you really can't afford to wait the minute or so for it to finish, use /dev/urandom - or /dev/random, if you've got access to sufficient entropy (did you pay extra for a hardware random number generator?).

jerf 16y ago

A coworker of mine pointed me to EncFS, which I think is generally a better idea because you don't commit to sizing in advance: http://www.arg0.net/encfs http://www.arg0.net/encfs I have been satisfied with its performance used as the backing store for virtual machine images, though not having a dual-core may be problematic.

jerf 16y ago
Would have edited if I could, but I'd also point out that EncFS is immune to all the problems thyrsus cited. It only requires FUSE privs, which are generally pretty easy to give.

sp332 16y ago

I'd use AES128, it's more secure (well, so far anyway). There's a weakness in the AES256 algorithm that makes it weaker then AES128. Not weak enough that I would really be worried , but if you have the choice...

nonUser 16y ago
schneier has more on that: http://www.schneier.com/blog/archives/2009/07/another_new_aes.html http://www.schneier.com/blog/archives/2009/07/another_new_ae...

thyrsus 16y ago

When would one use this? When I install Fedora, it gives me the opportunity to encrypt any file system other than /boot. Since this requires you to enter the password at boot, that's good for a laptop, probably bad for a server. You need root privilege to mount a loopback file system. Either (a) you've got the root password (b) the admin has given sufficient sudo privileges or (c) you use pam_mount to mount the encrypted filesystem (probably as your home directory). Am I missing other scenarios? The trouble with the pam_mount scenario is that the key for the file system needs to be based on your login password. Either your account creation process involves telling the admin your password, or someone's built a collection of self service tools I'm unaware of. Changing your password also means building a new encrypted filesystem, which again involves giving the admin the new password, or invoking self service tools I'm unaware of. If there are other scenarios in which to use this kind of encrypted file system, I'd appreciate hearing about them.

thefox 16y ago

Thx for your feedback.

nonUser 16y ago

Why do we need a script for this task? Yet another newbie script on HN...

rlpb 16y ago

This uses cryptoloop, which SHOULD NOT BE USED IF YOU WANT STRONG SECURITY. See: http://mareichelt.de/pub/texts.cryptoloop.php http://mareichelt.de/pub/texts.cryptoloop.php You can do better with LUKS or Truecrypt. LUKS comes with most distributions. It comes with a handy wrapper called "cryptsetup" which does the setup for you.