Authentication device intended to be used with an electronic device comprising a capacitive touchscreen and a radio transceiver, the authentication device comprising: - a light receiver disposed on a face of the authentication device, which face is intended to be placed facing the screen, - a radio transceiver, - a memory comprising an encryption key (243, 260), - a plurality of contacts (350, 351, 352, 360, 361, 362, 370, 371, 372) disposed on that face of the authentication device that is intended to be placed facing the screen, at least two contacts being made of a conductive material and forming a predetermined pattern associated with a first item of activation information, the other contacts being made of an insulating material, all the contacts having an identical appearance, - a first operating mode, called sleep mode, and a second operating mode, called active mode, the sleep mode being characterized by an energy consumption of the authentication device that is less than that of the active mode, the authentication device being designed to: - operate in the first operating mode, called sleep mode, - receive, via the light receiver, and decode a so-called activation light signal emitted by the screen, the so-called activation light signal encoding a message comprising a second item of activation information, - determine the validity of the received activation information, and, if the second activation information is identical to the first activation information, - shifting into the second operating mode, called active mode, the authentication device being designed to, in the second operating mode: - receive, via the light receiver, and decode a so-called identification light signal emitted by the screen, the so-called identification light signal encoding a message comprising an item of identification information, - transmit the identification information via its radio transceiver, - receive, via its radio transceiver, a request to establish a connection from the electronic device, and - establish the connection with the electronic device, - receive, via the established connection, a message comprising an item of information to be encrypted, - encrypt said information by using the encryption key, - sending a message to the electronic device, the message comprising the encrypted information. - a light receiver disposed on a face of the authentication device, which face is intended to be placed facing the screen, - a radio transceiver, - a memory comprising an encryption key (243, 260), - a plurality of contacts (350, 351, 352, 360, 361, 362, 370, 371, 372) disposed on that face of the authentication device that is intended to be placed facing the screen, at least two contacts being made of a conductive material and forming a predetermined pattern associated with a first item of activation information, the other contacts being made of an insulating material, all the contacts having an identical appearance, - a first operating mode, called sleep mode, and a second operating mode, called active mode, the sleep mode being characterized by an energy consumption of the authentication device that is less than that of the active mode, the authentication device being designed to: - operate in the first operating mode, called sleep mode, - receive, via the light receiver, and decode a so-called activation light signal emitted by the screen, the so-called activation light signal encoding a message comprising a second item of activation information, - determine the validity of the received activation information, and, if the second activation information is identical to the first activation information, - shifting into the second operating mode, called active mode, - operate in the first operating mode, called sleep mode, - receive, via the light receiver, and decode a so-called activation light signal emitted by the screen, the so-called activation light signal encoding a message comprising a second item of activation information, - determine the validity of the received activation information, and, if the second activation information is identical to the first activation information, - shifting into the second operating mode, called active mode, the authentication device being designed to, in the second operating mode: - receive, via the light receiver, and decode a so-called identification light signal emitted by the screen, the so-called identification light signal encoding a message comprising an item of identification information, - transmit the identification information via its radio transceiver, - receive, via its radio transceiver, a request to establish a connection from the electronic device, and - establish the connection with the electronic device, - receive, via the established connection, a message comprising an item of information to be encrypted, - encrypt said information by using the encryption key, - sending a message to the electronic device, the message comprising the encrypted information. - receive, via the light receiver, and decode a so-called identification light signal emitted by the screen, the so-called identification light signal encoding a message comprising an item of identification information, - transmit the identification information via its radio transceiver, - receive, via its radio transceiver, a request to establish a connection from the electronic device, and - establish the connection with the electronic device, - receive, via the established connection, a message comprising an item of information to be encrypted, - encrypt said information by using the encryption key, - sending a message to the electronic device, the message comprising the encrypted information.