Dropbox & EncFS on OS X Lion

I previously wrote about a method for creating a super-secure filesystem using Dropbox’s cloud storage.

After updating to Mac OS Lion I struggled to get the MacFusion GUI to work and so I wrote an application to automate the mounting and unmounting of the EncFS filesystem.

I also took the opportunity to switch from the now abandoned MacFUSE to Fuse4X, which is a properly maintained fork of MacFUSE started in June 2011.

The install procedure is much simpler than before, you install Fuse4X and EncFS, but instead of using the MacFusion GUI you just call my script instead.

To the instructions!

First download and install Fuse4X and a version of EncFS which uses the Fuse4X APIs. Thanks to Simone Lehmann for providing an EncFS Mac installer at http://www.lisanet.de/?p=128 (also mirrored here).

To create a new encrypted volume (stored locally at first to prevent the EncFS key from being synchronised with Dropbox):

encfs ~/Desktop/_Encrypted ~/Documents/_DropSec

Answer ‘yes’ when prompted to create the new folders and choose ‘p’ for pre-configured paranoia mode (256-bit AES encryption). Enter a secure EncFS password when prompted and you’re done.

Now the filesystem has been created we can deal with securing the key.

umount ~/Documents/_DropSec
mkdir ~/.keys
mv ~/Desktop/_Encrypted/.encfs6.xml ~/.keys/dropsec.xml

The commands above move your key from the EncFS filesystem into a hidden folder in your (local) home directory

Now move the entire ~/Desktop/_Encrypted folder (minus your key) into your Dropbox:

mv ~/Desktop/_Encrypted ~/Dropbox/

Finally download my DropSec application and copy it to your Applications folder.

The first time you run DropSec it will prompt you for your EncFS password which it stores in your local login keychain. The password must match the secure password you set in a previous step.

To mount or unmount the encrypted filesystem simply run the DropSec app. For convenience copy it to your Mac OS Dock for quick access.


Securing Dropbox

After the well publicised Dropbox security failings, I started searching for a solution which would allow me to encrypt private data held in my Dropbox while still having easy access to it from my personal Mac.

I could create a Mac encrypted disk image but this would be unwieldy to manage and probably result in large file updates whenever any of the contents were changed.

A more elegant technical solution is to create an encrypted user-space filesystem. It’s a bit more work to setup and you will need a combination of tools, but it does allow for a much more flexible and manageable configuration.


/usr/bin/ruby -e "$(curl -fsSL https://raw.github.com/gist/323731)"
  • Install Apple Xcode – this can be downloaded from the Apple Developer site
  • Install the latest EncFS encrypted filesystem (v1.7.4 at time of writing):
sudo brew install encfs

I want to make this installation as secure as possible so I’m not going to store the EncFS key file on Dropbox. To accomplish this I use a neat trick.

We’re going to create a new encrypted volume, but do this locally first so the EncFS key is never synchronised with Dropbox:

encfs ~/Desktop/Secure ~/Documents/DropSec

Answer ‘yes’ when prompted to create the new folders and choose ‘p’ for pre-configured paranoia mode (256-bit AES encryption). Enter a secure password when prompted and you’re done.

Now the filesystem has been created we can deal with the key.

umount ~/Documents/DropSec
mkdir ~/.encfskeys
mv ~/Desktop/Secure/.encfs6.xml ~/.encfskeys/dropsec.xml

Remove the /usr/local/bin/encfs symbolic link …

rm /usr/local/bin/encfs

… and replace with a simple wrapper script.

Use a text editor to create the following script:

# Wrapper to EncFS
export ENCFS6_CONFIG="/Users/${MYUSER}/.encfskeys/dropsec.xml"

Don’t forget to make the new wrapper script executable:

chmod 555 /usr/local/bin/encfs

Create a dummy key to ensure that the Macfusion plugin will recognise the EncFS volume:

touch ~/Desktop/Secure/.encfs6.xml

Now move the entire ~/Desktop/Secure folder into your Dropbox:

mv ~/Desktop/Secure ~/Dropbox/

To check the secure volume settings use:

ENCFS6_CONFIG="/Users/youruser/.encfskeys/dropsec.xml" encfsctl info ~/Dropbox/Secure

To change your secret password use:

ENCFS6_CONFIG="/Users/youruser/.encfskeys/dropsec.xml" encfsctl passwd ~/Dropbox/Secure

Use the Macfusion GUI to mount and unmount the volume when you need it.

  • The EncFS Raw Path is /Users/youruser/Dropbox/Secure
  • The Passphrase is the password you gave when you created your EncFS volume
  • The Mount Point is the local (unencrypted) folder where you access your secure folder (in this example we have used /Users/youruser/Documents/DropSec)

You should now have an encrypted volume in your Dropbox which you access via your local ~/Documents/DropSec mount.

The security of the ~/.encfskeys/dropsec.xml key file is of paramount importance. This is the EncFS decryption key which must stay in that folder. If you delete this file then all your encrypted data is gone forever, so keep a secure backup somewhere else just in case.

UPDATE: Read this post for a new method of creating a secure Dropbox folder.