US Patent 8117449 Method to detect man-in-the-middle (MITM) or relay attacks

A method for detecting a communication relay attack involves the steps of counting a number of clock cycles occurring in a clock signal between transmission of two predetermined elements of data with a data transmission device, counting a number of clock cycles occurring in the clock signal between receipt of the two predefined elements of data and comparing the number of clock cycles counted by the data transmission device with the number of clock cycles counted by the data receiving device.