Sometimes you share your Mac with other people without using separate user accounts, or sometimes you just need an extra secure place to keep some valuable information. This guide will show you how to create a password-protected disk image file to keep your data in that is protected with encryption.
1. In your Applications folder find the Utilities folder and open Disk Utility
2. On the top of the Disk Utility window, click New Image.
3. Name the image and choose the location you would like to save it, then set the image size (there are predefined sizes and you set any size at the bottom of the drop menu under Custom…). Make sure you make your disk a size that is large enough to hold all the files you want to keep plus any anticipated expansion.
4. Select the level of encryption you’d like to use. 128bit is generally a good compromise for security and quick access. If you require the highest grade security, select 256bit. 256bit encryption will slow down read/write access to the files within your image.
5. For an image that will contain files you wish to edit you want to partition the disk formatted as a Hard Drive and keep the Format as read/write disk image.
6. Click Create and enter the password for the disk image in the following screen.
7. Now you will see the new image listed in the left pane of Disk Utility and also a removable disk icon on your desktop. Double click on the disk and move any files you want to secure inside of it.
When finished, simply eject the disk to close and secure it. When you want to access it again find the file where you saved it, double click it and enter your password. The removable disk will now be loaded in your finder and you can access all your protected files again.