How to protect your Mac's most secret stuff with an encrypted disk image

Given the countless reports of our data being exploited, many of us are increasingly concerned about protecting that data. In this movie I’m going to show you how to protect a collection of data on your Mac.

Launch Disk Utility and choose File > New > New Disk Image.

In the New Blank Image window that appears name your image—something like My Secret Stuff. From the size menu choose a maximum size for the image—the absolute most you think it will hold rather than what it will currently hold.

Choose an encryption type—either 128- or 256-bit AES (256-bit is more secure but takes longer to encrypt).

From the Image Format menu choose Sparse Disk Image. You create a sparse disk image because, unlike other kinds of images, it will only consume the amount of storage used by its contents. So, if I have a 100MB file in it, it will only consume 100MB. It can, however, expand to the maximum size I originally defined. If I created a read/write image or DVD/CD Master, it would consumer every bit of storage assigned to it, even though its contents might be a third of that storage.

Click on Create and you’ll be prompted for a password. Enter and verify one but disable the Remember Password in My Keychain option. You do this because you don’t want someone sitting at your computer to be able to double-click on the image to unlock it. Rather, you want to be prompted for a password every time you access it. Click OK.

You now have both the image and the mounted image on the desktop. Feel free to throw your most secret documents into this mounted image. Once it’s copied to the image, delete it from your Mac. Now unmount the image by dragging it to the Trash.

To later access your locked image, double-click on it and enter the password. There it is, complete with all your secrets.

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