3.7   Protecting Your Files With Encryption

Apple’s FileVault encrypts your whole hard drive or SSD, but it does not provide very granular security. Whenever your Mac is on, everything is unlocked. A rogue application or anyone with physical access to your Mac can access any file. And the contents of any folders synced with the cloud (Dropbox or iCloud Drive) are readable by the cloud storage provider.

DropDMG lets you use the same strong AES encryption technology to create a “mini vault” that protects a select group of files from prying eyes. Each group of files is stored on an encrypted disk image. This can either be instead of full disk encryption or as an extra layer of security on top of it. Each disk image can hold as many or as few files as you want and can have its own passphrase. You can unlock the files when you need to use them and the lock them again as soon as you’re done.

The files will be secure if your hard drive is stolen or if you send the disk image across a network. Yet they are still fully accessible in all your Mac applications and searchable via Spotlight after you’ve entered the passphrase.

To create an encrypted disk image

Choose New Blank Disk Image… from the File menu. Set an encryption level and passphrase. A white volume icon will appear in the Finder. You can move existing files onto the disk image or create new ones there.

To lock your encrypted files

Click the eject button next to the white volume icon in the Finder’s sidebar.

To access your encrypted files

Double-click the disk image file. macOS will ask for the passphrase, and it can optionally remember it in the keychain. DropDMG’s Mount Image… command provides additional options.

Tip: You can save time by creating a Login Item to make some encrypted files available whenever you log into your Mac. Choose System Settings… from the Apple menu. Click on Accounts, and then select your account. Then click Login Items. Drag your .dmg file into the list. Now, whenever you log into your Mac, it will mount the disk image.

Tip: If you copied existing files to the encrypted disk image, you may want to remove any traces of the unencrypted files from your drive. To do this, put the originals in the trash and choose Finder ‣ Secure Empty Trash… or use the Erase Free Space… button in Disk Utility.