Abstract: An approach for defending radio frequency identification (RFID) tags and other contactless cards against ghost-and-leech (a.k.a. proxying, relay, or man-in-the-middle) attacks incorporates gesture recognition techniques directly implemented with the RFID tags or contactless cards. These tags or cards will only engage in wireless communications when they internally detect “secret handshakes.” A secret handshake recognition system is implemented on a passive WISP RFID tag having a built-in accelerometer. This approach is backward compatible with existing deployments of RFID tag and contactless card readers and is also designed to minimize the changes to the existing usage model of certain classes of RFID and contactless cards, such as access cards that are kept in a wallet or purse, by enabling execution of secret handshakes without removing the card. This novel approach can also improve the security and privacy properties in other uses of RFID tags, e.g., contactless payment cards.