This post shows step by step how to create an encrypted disk image. The Disk Image utility is a pre-bundled application, sold with every copy of Mac OS X Tiger (10.4). Popular pre-sized images, such as CD,DVD (4.7 GB), DVD (8.0 GB) can also be burned, making this a good technique for backups, particularly if you have sensitive information on them.
The encryption used is AES-128 bit, which is very strong. A brute force key decryption attempt, even with large clusters of latest/greatest supercomputers, would still take beyond any of our lifetimes. Do not lose the key as their is no way to get the data back!!!!
Disk Utility is a handy app, though powerful. You can do many useful things with this application, including accidentally erase a hard drive, so be careful. It will warn you before you do anything, but be aware of it’s powers.
Load up Disk Utility.
Open a finder window and navigate to Applications-> Finder -> Utilities -> Disk Utility.
Applications -> Finder -> Utilities -> Disk Utility
Press the “New Image Button”
Locate the drop down menu labeled ”Encryption”, and from it, select “AES-128 (recommended)”. Select the size you want the image. I like (4.7 GB or 8.0 GB for DVD burning). If your hard drive does not have enough room, the option will be gray.
Select Size of Image
Select a folder to place your logically named image. Press Create. When prompted, enter a quality password that you won’t forget, and write it down somewhere safe. DO NOT LOSE THE KEY!!!
Enter in a key. Don
Grab a sandwich while the computer builds the image. After sandwich, this is what Disk Utility will look like:
Sandwich Time!
When it finishes building the image, drag the files you want on the image into it. Unmount the image (eject it)
Eject the image
Drag the image into the left side of the Disk Utilty window, unless it is already there. Click on the image, highlighting it.
Now, you could be happy with this and leave it as that. But, if you chose to, for example, burn this to a DVD or CD… Here are the steps to continue.
Select the image labeled with the extension “DMG”, and press the BURN button on the top menu bar.
If your prompted to allow access to the keychain, allow it. Insert a blank disk, press BURN, and it will report back if the burn completed successfully.
Now you have a backup on different medium, that nobody can access unless they have the key defined previously. Not even Very Smart people with supercomputers can crack AES type encryption, so people utilizing this algorithm should sleep at night.