Relay attack

A relay attack (also known as the two-thief attack)[1] in computer security is a type of hacking technique related to man-in-the-middle and replay attacks.

In a classic man-in-the-middle attack, an attacker intercepts and manipulates communications between two parties initiated by one of the parties.

In a classic relay attack, communication with both parties is initiated by the attacker who then merely relays messages between the two parties without manipulating them or even necessarily reading them.

Peggy works in a high-security building that she accesses using a smart card in her purse.

When she approaches the door of the building, the building detects the presence of a smart card and initiates an exchange of messages that constitute a zero-knowledge password proof that the card is Peggy's.