The document discusses the transaction timer feature of MIFARE DESFire EV3 and MIFARE Plus EV2 contactless smart cards. The transaction timer allows a card issuer to configure a maximum time limit for transactions, to mitigate man-in-the-middle attacks. It works by automatically resetting the card and aborting the transaction if the time threshold is exceeded. Transaction timers can be set individually for each application. The feature enhances security without requiring changes to existing reader terminal infrastructures.