Mac OSX Encrypted Disk Images

One of the easiest and most secure ways to store your data on your Mac is by using the built-in Encrypted Disk Image. I use this to store financial data, etc. As long as my disk image is not mounted, my documents are secure. If I lose my Mac, this data is secure. In fact, I’ve even used getdropbox.com to back up my encrypted disk images and to keep copies on multiple computers. Here’s how to create a password-protected (encrypted) disk image in Mac OS X:

1. Open Disk Utility (/Applications/Utilities/).
2. Mac OS X 10.4, 10.5 or later: Click the New Image button, or choose New > Blank Disk Image from the Disk Utility File menu.
Mac OS X 10.3 through 10.3.9: Choose New from the Disk Utility Image menu.

3. Enter a name in the Save As field. This name is used for the disk image (.dmg) file.
4. Change the save destination if you wish to.
5. Select a size for the image file from the Volume Size pop-up menu (Size in Mac OS X 10.3) .
6. Choose a volume format if you don’t want to use the default Mac OS X Extended (Journaled).
7. Choose an image format. You can use “sparse disk image” for a disk image that only uses as much space as it needs, rather than a set amount of space. If you’re not sure, use “read/write disk image” choice.
8. Choose 128-bit AES (and/or 256-bit AES in Mac OS X 10.5 or later) from the Encryption pop-up menu to encrypt the image’s contents with a password. If you don’t choose an encryption, your new image won’t be encrypted.
9. Click the Create button.
10. Enter and verify a good password in the dialog window that appears. This password will be saved in your keychain by default, or you can deselect “Remember password (add to keychain)” if you don’t want that. You can store the password in the keychain both for convenience and for reducing risk of password loss.
11. Click OK.

This information was taken from Apple’s official documentation, which you can view here.

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