A method of authenticating a transponder communicating with a server, including: calculating a one-time password in the transponder with a dedicated algorithm, on the basis of the state of a counter and a physical quantity, such as a transmission delay determined in the transponder during reading by a reading device; transmitting the password to the server by the reading device, which determines a transmission delay of the transponder, and transmitting to the server, in addition to the password, the information about the transmission delay determined in the reading device; decrypting by the dedicated algorithm the password, and checking if the decrypted transmission delay of the received password corresponds to the transmission delay determined by the reading device within a determined temporal margin, and if the state of the counter is different from a received previous state of the counter so as to authenticate the transponder.