The word "authentication" refers to the process of proving the identity of someone or something. This is a crucial part of securing an extranet because without it there can be no access control to the information and services available over an extranet. Many people are used to being "authenticated" or to having their identity proven when they attempt to cash a check at a bank and have to present a photo ID to the bank teller in order to prove that they are who they say they are or when they have to enter a personal identification number in order to prove that they are who they say they are when conducting a financial transaction over a touch tone telephone.

There are three categories of authentication and three types of authentication techniques that apply to the Internet, intranets, and extranets. All of these will be discussed in this chapter.

Anyone who has used a time share system has encountered user to host authentication in which users must prove their identity to a host computer in order to access the information and resources available on the host machine. Similarly, one host must authenticate or prove its identity to another host in order to access the information and resources available on another host machine. User to user authentication in which one user must prove his or her identity to another user in order to access the information and resources of the other user plays a large part in...