In a method of establishing a secure communication link between a first terminal and a second terminal, the first terminal is connected to a third terminal which can be connected to a mobile telephone network and the second terminal is connected to an authentication element of the telephone network. The method includes: transfer of an authentication datum from the third terminal to the network authentication element; following authentication of the third terminal, the transfer of a random variable from the network authentication element to the third terminal; the parallel generation of a session key by the third terminal and the network authentication element from the random variable; the generation by the first and second terminals of a shared key from the session key; and the opening of a secure communication link with the use of the shared key.