Classical Cryptography

Humans have been hiding messages from the very first moment they started sending messages. In the early ages, messages were sent between leaders, emperors, conquerors, kings, and so on, in the form of verbal messages through a human messenger. Although unspoken rules protected the human messengers, sometimes this rule was not followed, and the messenger was caught by enemies. At that point, all the enemy needed to do was send an altered message to the rightful receiver. This is a real-life example of a man-in-the-middle attack.