How to quickly encrypt and securely delete with Disk Utility

Reader Bob Ross is interested in encryption. In anything-but-cryptic fashion he writes:

I want to quickly encrypt one folder at the end of the day. Disk Utility is too much trouble and amazingly doesn't securely delete the original folder at the end. Surely, there is a short AppleScript or application out there that encrypts a folder and securely deletes the original folder?

There are third-party utilities such as AgileBits' $35 Knox and Tao Effect's $35 Espionage 2 that can encrypt small bits of data like this for you, but I'd like to take a moment to revisit Disk Utility.

And I take that moment because it really isn't terribly difficult to do this nor do you need to be left with an unsecured folder. Try this:

Launch Disk Utility and choose File -> New -> Blank Disk Image. In the New Blank Image window that appears name your image, choose a size for it (something roomy enough to accommodate all the files you're likely to move to it), select 128- or 256-bit encryption from the Encryption pop-up menu, and select Sparse Disk Image from the Image Format pop-up menu. I suggest choosing sparse disk image because your disk image will take up only as much storage as the sum of the files within it. So, even though you've created a 2.5GB image, if you've only flung a single 300MB file into it, that's the size it will be. (It can hold up to 2.5GB but won't stretch beyond that boundary.)

When you click Create you'll be prompted to enter and confirm a password for the image. Do not enable the Remember Password in my Keychain option. (If you do, anyone sitting down at your computer can mount the image.) Click OK and the image file appears where you've saved it along with its mounted disk image. Just drag files and folders to the mounted image to save them. At the end of the day, drag the mounted image to the trash and you're good to go - the original encrypted image remains on your Mac but you must double-click it and enter the password in order to mount its disk image and reveal the files and folders within.

If you're concerned that you may forget to eject the mounted disk image Automator can help. Just create a new Automator workflow that uses an iCal alarm. Add two actions to it - Get Specified Finder Items and Eject Disk. Drag your mounted disk image to the first action. When you save the workflow, iCal will launch and you'll see your workflow as an event in the Automator calendar. Configure the event to repeat every day at the time when you want the image to be ejected. Done.

Safer still? Place your folder on a key drive that you jack into your Mac every day. Take it with you at the end of the day.