Encrypting data is a good idea if you use a portable Mac because it’ll mean that even if a thief or hacker gets hold of the data, he or she won’t be able to do anything with it.
The type of encryption offered by OS X is theoretically unbreakable. Using FileVault Perhaps the most comprehensive solution is to enable FileVault full-disk encryption in the Security pane of System Preferences (Apple menu→System Preferences → Security & Privacy), which ensures that all data on your hard disk is encrypted.
However, this can result in about 10 percent slower disk access compared to an unencrypted disk—not enough to notice during everyday use, but it will affect periods of prolonged disk access, such as when you’re booting up.
As an alternative to FileVault, you can create an encrypted archive. This is like a container file that you can save files into, a little like a USB memory stick except it’s just a file. You can mount and unmount the file whenever you want to add, remove, or view files within it.
Mounting is done by simply double-clicking the file and entering the password when prompted. To unmount it, just click the Eject icon next to its entry in the sidebar of Finder—just like you eject a USB memory stick when you’ve finished with it.
Because it’s just a file, the encrypted archive can be transferred to a USB memory stick and should be compatible with other Mac computers (including those running recent versions of OS X, such as Lion and Snow Leopard).
Once the encrypted archive is created, you can rest safe in the knowledge that— without the password—absolutely nobody will be able to access the data inside it.
Creating an Encrypted Archive: Step by Step
Here are the steps required to create a password-protected archive:
- Start Disk Utility, which you can find in the Utilities folder within the Applications view of Finder.
- On the Disk Utility toolbar, click the New Image button.
- In the dialog box, type a filename for the archive into the Save As field, and beneath that choose a location where you want to save the archive. Type the same name in the Name field below— this is what’ll appear in Finder whenever you mount your new archive.
- In the Format dropdown list, select MS-DOS (FAT). This gives you the ability to create smaller archive containers compared to using Mac disk formats. Don’t worry if this sounds less than perfect—FAT is the same disk format used on USB memory sticks and photographic memory cards. Your Mac is 100 percent compatible with it.
- In the Size dropdown, select an archive size. Even if they’re empty, OS X archives are still full size. In other words, a 2.5 MB archive will always be 2.5 MB, even if there’s only a tiny 10 KB file in it, and they don’t expand and contract to fit their contents. Choose a size that fits your needs.
- In the Encryption dropdown list, select 256-Bit AES Encryption. This is an extremely secure form of encryption that’s as strong and unbreakable as you could need. It’s a little slower if you’re saving massive files to archives, so if you intend to encrypt huge video files and are also impatient, you might like to select the 128-Bit AES Encryption option. This choice is also extremely secure.
- Leave the other fields as they are, and click the Create button to begin making the archive.
- Soon after this, you’ll be prompted to create the password for the archive. You’ll need to type it twice. Don’t forget this password! If you do you’ll never be able to access its contents again. The form of encryption used by OS X is unbreakable.
- By checking Remember Password in My Keychain, you can avoid being prompted for the password each time you mount the archive. However, this will mean anybody with access to your computer (for example, somebody walking past) can also mount the archive without being prompted for a password. Once you’re done, click the OK button.
- The archive will now be created. To test it, double-click the archive image and enter the password when prompted. It’ll appear as a volume in Finder and will be listed under the Devices heading in exactly the same way as if you’ve inserted a memory stick or a digital camera, and you can drag/drop files into it. Don’t forget to eject the disk image after you’ve finished using it by clicking the Eject icon next to its entry in Finder.
You can create aliases to any file within the archive which, when double-clicked, will automatically mount the archive, prompt you for a password (if it’s not in the keychain), and load the file.
To do so, drag and drop a file from the archive to the desktop, but before releasing the mouse button, press and hold OPTION+COMMAND. When you release the mouse button, an alias to the file will be created. However, don’t forget to eject the archive when you’ve finished working on the file!