Mac® Security Bible

5.2. What Keychains Can Store

Keychains are for keys, but what exactly does that mean? The digital data you can store securely in a keychain falls into several major categories.

5.2.1. Passwords

Without a doubt, the vast majority of items you store in your keychain are passwords of one kind or another. Each password in a keychain also includes the associated username (if any) and the location of the item — usually a URL or an IP address. A keychain may contain passwords such as the ones needed for the following:

• Local servers, including other Macs on your network using file sharing, screen sharing, and other shared services

• Remote file servers, including FTP servers and WebDAV servers, among many others

• Mail servers

• Websites (nearly any website that requires you to log in with a username and password)

• MobileMe

• Wireless networks

• AirPort base stations and Time Capsule devices

• Applications that use encryption or that must access password-protected network services on your behalf (including chat, blogging, synchronization, and telephony applications, among others)

• Encrypted disk images

• VPN services

5.2.2. Public keys, private keys, and certificates

Although passwords are fairly self-explanatory, some of the other objects stored in keychains may be less well-understood. The next set of items has to do with verifying someone's identity in a different manner than simply asking for a password.

Public key cryptography is a clever way of encrypting data without the sender and recipient ever having ...