A man-in-the-middle attack (abbreviated to MITM, also known as a grandmaster attack) is when an attacker intercepts communications between two parties and changes them to suit their own purpose. By impersonating communications from both parties and ensuring that the communications continue, both parties believe that they are directly messaging each other until it is too late.
MITM attacks can be stopped by using encrypted communications between the two parties, unless the attacker is able to break the encryption being used.
This is also known as a grandmaster attack, with the name coming from a technique for an unskilled chess player to take on two grandmasters at the same time and ensure that they can only lose at most one game. This is done by keeping the grandmasters separate from each other, with the unskilled player simply repeating the moves of each grandmaster against the other player.
Last updated: 16 October 2017