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3.7   Protecting Your Files With Encryption

Apple’s FileVault encrypts your whole hard drive (Mac OS X 10.7) or home folder (Mac OS X 10.6 and earlier). This is overkill for many users, needlessly slowing access to files and increasing the risk of data corruption. Additionally, whole drive encryption does not secure your files from other user accounts on the same Mac.

DropDMG lets you use the same encryption technology to protect a select group of files from prying eyes. Each group of files is stored on an encrypted disk image. Each disk image can hold as many or as few files as you want and can have its own passphrase. The files will be secure if your hard drive is stolen or if you send the disk image across a network. The files will be 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. Mac OS X 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 Preferences… 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.

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