How Do I Encrypt Files In Mac OS X?
The easiest way to encrypt and decrypt files in Mac OS X is with FileVault. To turn on FileVault, click on the Apple menu on the top left of the screen and select System Preferences. Click on the Security panel and then the FileVault tab.
FileVault lets you set a master password on top of your login password to encrypt your entire home folder. Your files will automatically be encrypted and decrypted as you use them.