Abstract: In connection with authenticating a client of a network, information is acquired that characterizes the client in a manner that enables a determination about authenticating the client of the network, the information being acquired other than in the form of a digital message that is passed on behalf of the client to the network; an authentication decision is made based on the information. Information is encrypted in a manner that is based on a physical property of an intended recipient of the information, and delivering the encrypted information to the recipient. A source of a beacon is physically associated with a person, times of receipt of the beacon at multiple stations are measured, and the location of the person is determined based on the times of receipt.