You can use Disk Utility to encrypt removable drives to prevent other people from accessing your data, but that requires you to navigate Disk Utility’s many options, menus, and buttons. In Mountain Lion, the process is much easier, and in this week’s video, I show you how to do it. I also show you how to encrypt your Time Machine backup drives.
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Senior contributor Kirk McElhearn covered this topic and explained how to encrypt drives using Terminal in a Mac OS X Hints article.
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(Note: An assumption made in the video, but not mentioned, is that the drive you want to encrypt is formatted as a Mac drive with a GUID Partition Table. If your drive is not properly formatted, follow Steps 1 through 10 under “Erase and reformat the storage device” in this Apple support article—ignore the rest of that section, and ignore the rest of the article, as they don’t apply here.)
OS X has long let you use Disk Utility to encrypt removable drives to prevent other people from accessing your data. But in Mountain Lion, the process is much easier. With the drive connected to your Mac and mounted in the Finder, right-click or Control-click on the drive—either on the desktop or in a Finder-window sidebar—and choose Encrypt. (The command includes the name of the selected drive; in this example, Encrypt SanDisk 2GB.) Don’t worry, any data on the drive is preserved.
You’re prompted to provide a password that you’ll use to access the drive once it’s been encrypted. Type the desired password twice, then provide a hint in case you have trouble remembering the password. A warning here: If you forget the password, you won’t be able to access the drive—there’s no “master password” for encrypted drives as there is for OS X user accounts. Click Encrypt Disk.
The encryption process is slow. For example, on a 2GB thumb drive, it took roughly three minutes for me; on a 1TB hard drive, it can take an hour or more. And unfortunately, there’s no progress bar indicating the status of the encryption. If your drive has an activity light, the light will stop flashing when the encryption process is complete. You can use the Finder’s Get Info command to confirm that your drive is encrypted.
Once a drive is encrypted, whenever you connect it to a Mac running Lion or later, you’ll need to provide the drive’s password to access the drive’s contents. (You can save the password in your account’s keychain so you don’t have to enter the password on your own computer in the future.)
If you ever want to remove encryption, so the drive is accessible by anyone, just right-click or Control-click the drive and choose Decrypt. Again, the process takes a while, so you’ll need to be patient.
Here’s a bonus tip: You can also easily encrypt your Time Machine backup drives. To do so, connect a backup drive and open the Time Machine pane of System Preferences. Click Select Disk, choose the backup drive, and then check the box to Encrypt Backups. Click Use Disk, and OS X will encrypt the drive and prepare it for use by Time Machine. Again, any existing backup data is preserved.
As with other encrypted drives, whenever you connect your encrypted Time Machine drive, you’ll need to provide its password to mount it; once you do, Time Machine will use it for backups like any other drive.
Updated 9/29/12, 6pm, to add note about the GUID-partition-map requirement.