Relay attack
An attack in which two devices forward the radio traffic between a card and a terminal that are far apart.
Cryptography does not help, because the attacker does not need to understand anything. One device sits near the victim's card in a pocket, another against a terminal in a different shop, and the messages pass between them untouched. The card believes it is next to the terminal, and the terminal believes the same of the card. Gerhard Hancke demonstrated it against ISO 14443 cards in 2005, and the same trick opens cars with keyless entry.
The countermeasure is measuring time. Mastercard added a relay resistance protocol to its contactless kernel, in which the terminal times the card's reply and gives up if it is too slow for a signal that only travelled a few centimetres. In 2021 researchers at Birmingham and Surrey showed that Apple Pay's Express Transit mode could be relayed with a Visa card on a locked phone.