Man-in-the-middle attack

In a man-in-the-middle attack on a communications system, the attacker is the man-in-the-middle. He deceives the victims so they think they are communicating with each other but in fact both are talking to him. It is an active attack; the attacker needs not only the ability to intercept messages, but to insert his own and to prevent delivery of genuine ones.

Conventionally, the communicating parties are A and B or Alice and Bob. Let us call the attacker Edward, for Eavesdropper or EvilDoer.