Authentication of an electronic tag

A method for authenticating an electronic tag by a host communicating with the electronic tag via a reader, the method comprising:

• extracting from the electronic tag data to be transmitted to the host;
• transmitting the data to the host via the reader, while storing the data on a host side and on a reader side;
• generating, on the host side, a random or pseudo-random number and transmitting the random or pseudo-random number to the electronic tag via the reader, while storing the random or pseudo-random number on the host side, on the reader side, and on an electronic tag side;
• calculating, on the electronic tag side, an intermediary signature by application of at least one first function shared by the electronic tag and the reader to the random or pseudo-random number, the data and at least one first secret key known by the electronic tag and the reader only;
• calculating, on the electronic tag side, a first combination of XOR type of the intermediary signature with a second secret key, to obtain a first digital signature to be transmitted to the reader, wherein the second secret key is known by the electronic tag and the host only;
• transmitting the first digital signature to the reader;
• calculating, on the reader side, a second combination of XOR type of the received first digital signature with the intermediary value to obtain a result of the second combination;
• calculating, on the reader side, a second signature by application of a second function to the result of the second combination, the random or pseudo-random number and the data, wherein the second function is a pseudo-random number generation function, common to the reader and to the host, and wherein the pseudo-random generation function uses as seeds the data, the random or pseudo-random number and, respectively on the reader side and on the host side, the second combination and the second secret key;
• transmitting the second signature to the host;
• and
• checking, on the host side, a coherence between the second signature and a validation value calculated from the second function and the second secret key.