A relay attack is a type of radio-based man-in-the-middle attack in which the attacker acts as a relay station
in the radio link between the radio key and the application system. Relay attacks are similar to replay
attacksand man-in-the-middle attacks and are aimed at intercepting information transmitted with the radio signals between the key owner and the secured and locked car, home or workplace. The attacker joins the communication and copies the key code for a keyless front door, Remote Keyless Entry (RKE) or Passive Entry Passive Start (PEPS) of a motor vehicle without modifying the message
, but to use it at a later time with a fraudulent intent. In a relay attack, the attacker switches into the radio link and routes the signals from the smartphone, which mimics the radio key, to the smart key module, from which it must infer that the smartphone is near the motor vehicle and opens the car door. To prevent such attacks
, the smart key module can accurately determine the distance between the vehicle and the radio keys, which would allow an attacker to intercept the radio signal from a key fob and use it later to open the car or steal it. Relay attacks can be targeted at the access code for remote keyless entry of motor vehicles, but also at contactless smart cards.