How do I password protect a set of files with an encrypted disk image?

This article will teach you how to password protect files with an encrypted disk image for free, using Disk Utility on your Mac. This allows you to hide sensitive files, like your tax returns or embarrassing photos. Encrypted disk images are also a safe way to keep confidential files on CDs or USB flash drives for use with Macs (but these are not Windows compatible).

1. Open Disk Utility. It's located in Applications > Utilities. 
2. Press the New Image button or go to the menu and select File > New > New Blank Disk Image.
3. Choose a name for your encrypted disk image and a location to store it.
4. In Volume size, choose the largest capacity you will allow your encrypted folder to grow into. Try 4.7 GB or less so you can burn your encrypted files onto DVD for safe keeping.
5. In Encryption, choose at least "128-bit encryption." If you're running 10.5 or later, you can chose "256-bit encryption" for industrial strength protection.
6. In Partitions, choose "CD/DVD" if you plan to burn the folder onto a disk in the future. Otherwise Intel-based Mac users select "GUID Partition Map" and PowerPC-based Mac users (G4, G5) select "Apple Partition Map." (You may not have this option at all if you're using OS 10.4 or earlier.)
7. In image format, choose "sparse bundle disk image" if you plan to use this data with Macs running OS X 10.5 or later. If you want your image to be backwards compatible with older Macs, choose "sparse disk image." Sparse disk images grow as you add files to them, up to the volume size you set above. (They don't automatically shrink when you remove files, you'll have to use Disk Utility to resize the image.) Sparse bundle disk images were introduced in Mac OS X 10.5 Leopard because they make it easier to back up encrypted files with Time Machine.
8. Click Create.

9. Enter a memorable password that is different from your user account's password. If you forget your password, you will no longer be able to access these files.
10. VERY IMPORTANT:  Uncheck the box to " Remember password in my keychain."  If your disk image's password is stored in your keychain, then anyone logged into your user account can access your sensitive files.

Now drag and drop the files you want password protected into the new disk image. Eject the disk image (in the same way you would eject a CD) to encrypt your files. To access your files again, double-click the disk image and enter your password. Your Mac will give you the option to remember your password in the keychain each time, but don't do it! Remember to back up these important files to a CD/DVD, external hard drive, USB flash drive, or online storage service like MobileMe.

Published June 22, 2009 1:36 PM
Last modified on June 23, 2009 5:10 PM