ABSTRACT
Authentication (more precisely, entity authentication) is the process of identifying an entity in a reliable manner. It provides a means to verify that an entity is indeed who it claims to be. The most common technique for verification is to check whether the claimant possesses a “secret” that a genuine entity is supposed to. In an everyday situation of making a telephone call, we authenticate the person answering the phone by his/her voice. The “secret” here (voice) is a quality inherent to the person. We can identify people already known to us by their visual appearance. But authentication gets complicated 88when we do not have voice and/or sight of appearance to help identify the person we are trying to communicate with. For example, a computer trying to authenticate a human user or two computers (communicating on behalf of two human users) trying to authenticate each other.
