Patent ID: 8198984

Claim:
A method for communicating securely between a reader and at least one tag in an RFID system, the method comprising: switching, at the reader, on an electromagnetic signal for energizing the RFID tag and/or transmitting an instruction or first data to the tag; generating, at the tag, a random number, converting said random number into a random time period and, transmitting a response to the reader after a delay time that corresponds to the random time period; measuring, at the reader, the time period between said switching on of the electromagnetic signal or said transmitting of an instruction or first data to the tag and receiving of the response from the tag, which time period corresponds to the random time period, reconverting the measured random time period into the random number, encrypting second data to be sent to the tag by the use of the random number and transmitting said encrypted data to the tag; at the tag, decrypting the received encrypted data by the use of the random number.