Authentication insures that a user is who they say they are.
Authorization limits a user's access to data and protocols.
Integrity assures that information has not been modified by unauthorized parties. Privacy assures that information cannot be read by unauthorized parties, particularly when using shared media. Firewalls allow authorized users access to a network or computer system. Dial back modem access insures the source of a connection request. Integrity Check Values are checksums computed via keyed algorithms.