How to keep things secure in your Dropbox or other cloud storage

I'm a huge fan of Dropbox and other cloud services.  It's just incredibly convenient to be able to access my stuff from all my machines.

But security and privacy remain problematic: If your stuff is stored on someone else's machine, who else can access it?  The question has been in the news lately.  Expect more such stories as adoption of cloud technologies accelerates.

Yet by far the largest risk to your data is loss from hardware failure, theft or physical disaster.  Aside from the convenience factor, storing things in your Dropbox means it's locally copied to all your machines as well as safely backed-up (and versioned!) in the cloud.  For those reasons, I keep all my current work in my Dropbox.  Securely!

Here's How:

I use Macs most often lately, and this tip leverages some truly keen capabilities of OS X.  (I am unaware if Windows 7 offers similar functionality combined with similar ease and baked-in speed, but there are third-party tools like TrueCrypt which can attempt something kinda/sorta parallel, but not as easy or automagical, and not as swift in execution.)

Disclaimer: a patient Bad Guy could probably hack any encryption, and it probably serves as a minor inconvenience at best to any of several three-letter agencies.  But, I suspect that should I be of sufficient interest to such folks that they'd be groping my digital giblets rather than just fondling my carbon-based ones at airports, encryption strategy would be the least of my worries.

Next:

• Open Disk Utility.  (It's in your Applications | Utilities folder, or just go to Spotlight and type "disk utility.")
  
• Click the New Image button.
  
• A form will pop up.  Fill it out as follows.  You're creating a sparse bundle disk image-- a virtual disk divided into small files (more backup- and Dropbox-friendly than a monolithic disk image would be).  Give both the image and the virtual disk that will appear on mounting it sensible names (via the "Save As" and "Name" fields, respectively).  Choose the size as-desired.  Select Mac OS Extended (journaled) as the format and a single Apple Partition Map as the partition.  Choose 256-bit encryption if you're uber-paranoid, or consider the faster 128-bit.  Select a size that's adequate but not obese for your purposes.

• Click the Create button.  You'll be prompted to enter a password.  Do so (twice) and be sure to UNCHECK the "Remember password in my keychain" so you'll be prompted for the passcode each time you mount the disk.  You want that behavior.

• Click OK.  The disk will mount and appear on your desktop, and Dropbox will begin uploading it to its servers (and then down to any of your other linked computers).
  
• Now do whatever you want to do.  Put stuff in the disk as usual. 
  
• Here's the automagical part: you can make aliases to any item that's inside and put the alias wherever you want-- on your desktop, for example.  Clicking on such an alias will automagically resolve to the encrypted disk, and you'll be prompted for its password if it isn't already mounted.  Changes you make will automagically be stored in the encrypted disk.  You can, of course, mount the virtual disk manually by double-clicking on the sparsebundle in your Dropbox.  But you don't need to.
  
• Using this strategy, at no time does unencrypted information get transmitted (Dropbox connections are themselves encrypted) or stored on Dropbox.
  
• When you're done, "eject" the virtual disk (or, this will happen automatically when you shut down).  It is now unopenable and its contents unreadable by anyone lacking the password.

 You can now access your encrypted disk from any OS X Mac!  (To-date, encrypted disk images aren't supported by iOS... hope that changes.)

You can, of course, do the same thing without putting the sparsebundle in your Dropbox.  For example, I have a VMWare Fusion virtual machine with sensitive content installed on a 25GB encrypted sparsebundle on my external Firewire disk.  Thanks to OS X's deep integration of this functionality, it runs like a hose.


(Don't have Dropbox yet?  Get it at http://db.tt/Me4yRjt and I get a little space bonus... [grin].)