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Creating an Encrypted Backup to External Drive

April 26, 2008 by debbie T | Digital Photography • Mac Software

Note: This tutorial is for Mac OS X - I am using Leopard, but older versions of OS X would still work fine.

My photo files were getting out of hand. I had no problem backing up to my external hard drives, but I needed a better off site backup solution. I was using Amazon S3 for my original files, but there was so much meta data in iPhoto that I didn’t want to lose, like keywords, plus all the modified versions as well.

I regularly burned my photo files onto DVDs for storage at my parents’ home, but that was becoming time consuming and inefficient.

So, what to do? I decided to purchase another external hard drive to store at my husband’s office. But security was an issue. What if the drive was stolen? I needed to add a level of security to the drive in case it ended up in the wrong hands.

I searched online, and figured out that I could create an encrypted disk image (.dmg) file that could be saved on the external hard drive. I could use my syncing software Chronosync to regularly back up all my files.

First, set up the disk image on the external hard drive using Disk Utility

Choose File>New>Blank Disk Image

New-disk-img

Type a “save as” name. This will be the name of the file.
Browse to the location of your external hard drive. Don’t worry, because this is just like any other file, it can be copied or moved to a new location later.
Volume name: is the name of the mounted volume. I just left the default, but you can choose a more appropriate name.
Volume size: choose “custom” and type a slightly lower size quantity of your external hard drive. Make sure you choose “gb” from the pull down menu. For example, if your drive is 500gb, you might want to set a volume size of 460gb. If you don’t want all your files to be encrypted, then choose a smaller size. It is very flexible.
Volume format: I chose Mac OS Extended (Journaled)
Choose either 128 or 256 for encryption. I chose 256
The partition is where I got a bit confused. I chose Single Partition, but there could be other choices that are more appropriate. This is a new setting in Leopard, and all the Disk Image tutorials I found were older.
Lastly, choose “Sparse Disk Image” - this is something very cool that I just learned. It allows your disk image to be more flexible in size. For example, if you set your volume size for 30gb, and the files saved to the volume are only 10gb, the size of the disk image will be 10gb. It grows as you add files.

IMPORTANT NOTE: It has come to my attention that there could be problems using such a large sized file if a hard drive sector becomes corrupt. I don’t know if this is true or not, but I did find another program that might be a better solution.

TrueCrypt is an open source app for Mac, Linux, and Windows. It looks very intriguing. But for now, I will use my solution, and hope for the best.