Authentication

Abstract

It is obviously important to encrypt a transmitted message, but how can it be proved that the user who originally encrypted the message sent the message. This is achieved with message authentication. The two users who are communicating are sometimes known as the principals. It should be assumed that an intruder (hacker) can intercept and listen to messages at any part of the communications, whether it be the initial communication between the two parties and their encryption keys or when the encrypted messages are sent. The intruder could thus playback any communications between the parties and pretend to be the other.