Authorizing RFID reader and inhibiting skimming

In an RFID reader system including an RFID tag and an RFID reader, a method of authorizing the RFID reader, the method comprising the RFID tags performing the following steps:

• an initial-read signal receiving step of receiving a plurality of successively-transmitted RFID initial-read signals and determining respective initial-read signal characteristics of the received initial-read signals, wherein each characteristic is selected from the group consisting of a received power level of the respective read signal, the time interval between the respective read signal and a preceding or following read signal, and identification data included in the respective read signal, whereby each characteristic has a respective type of “power level,” “time interval,” or “identification data,” respectively;
• using the determined initial-read signal characteristics, automatically selecting an authorization sequence using a controller;
• an authorization-signal receiving step of receiving a plurality of successively-transmitted RFID authorization signals sequentially, and determining respective authorization-signal characteristics of the received authorization signals, wherein each characteristic is selected from the group consisting of a received power level of the respective authorization signal, the time interval between the respective authorization signal and a preceding or following authorization signal, and identification data included in the respective authorization signal, whereby each characteristic has a respective type of “power level,” “time interval,” or “identification data,” respectively;
• automatically comparing the determined authorization-signal characteristics to the authorization sequence using the controller, so that the RFID reader is authorized if the determined authorization-signal characteristics correspond to the authorization sequence;
• and
• after the initial-read signal receiving step and before the authorization-signal receiving step, listening for RFID read signals from a skimmer, and, if any read signals from a skimmer are detected, determining that the RFID reader is not authorized.