KEYCHAIN - Mac OS X Keychain File is used by Apple’s Keychain application to store a user’s encrypted passwords and provides for automatic login to websites or network resources. Apple keychain is bundled with Mac operating systems. In addition to passwords, keychain files may include certificates, private keys or other authentication data. Files can only be opened by the Apple Keychain application. Information is only stored in Keychain if users have selected the option in the operating system preferences.