Learn in the textbookAttacks on Networks and Communication Paths
DefinitionA man-in-the-middle attack (中間者攻撃) is one in which an attacker secretly places themselves between two communicating parties and eavesdrops (盗聴) on or tampers (改ざん) with the data they exchange.
ExplanationThe attacker poses as the server to the user and as the user to the server, passing data in both directions through their own hands. Because each side believes it is talking directly to the other, neither is likely to notice when the contents are read or altered on the way. Unencrypted traffic and connections made without checking whether the other side is genuine are easy targets, and the defenses are encrypting the traffic and confirming the other party is authentic, for instance by validating its server certificate.
AnalogyIt is like a messenger carrying letters between two people who quietly opens each one, reads it, adds a few lines, and then delivers it. The recipient has no idea the messenger tampered with it along the way.
Memory hookThe Japanese name is a direct rendering of "man-in-the-middle", shortened to MITM from its initials.