Methods, computer program products, and systems for use in near field communications systems for authenticating at a near field communications receiver, a user of a near field communications transmitter. The system includes a data receiver for receiving a signal comprising a first unique identifier from a near field communications transmitter. The system also includes a received signal strength indicator for measuring a signal strength of the received signal. The system further includes a signal strength tracker for tracking a variation with time of the signal strength of the received signal and converting the variation with time into a second unique identifier. The system further includes a comparator for comparing the received first unique identifier and the tracked and converted second unique identifier and for outputting a signal indicating the result of the comparison. The user is authenticated if the signal indicates that the first and second identifiers correlate correctly.