Abstract: A hardware authentication token is intended for being connected to a computer terminal. This token includes a confirmation button, a processor and a secure memory area where a first private key is stored. The terminal can ask the user to authenticate using the token by transmitting a first nonce to the user. After the confirmation button has been pressed, the token generates a second nonce, encodes it using ultrasonic signals and transmits it, via an acoustic channel, to the user's smartphone. The token determines from the response whether the second nonce has been signed with a second private key belonging to the user and, if so, returns the first nonce encrypted by the first private key to the computer terminal in order to authenticate the user.

Abstract: A physical device is designed to store digital keys for carrying out transactions on a blockchain. The physical device comprises a microphone, a loudspeaker, and a DSP processor comprising a secured element in which the pairs of secret keys and public keys are stored, the DSP also comprising an acoustic codec using a dictionary S containing words that represent random or pseudo-random ultrasonic signals stored in the memory of the DSP. The DSP is designed to decode a message consisting of words from S, received from an acoustic channel via the microphone, to sign the thus decoded message by a private key and to transmit the signature obtained in this way in the form of a response consisting of successive words from S, over the acoustic channel, via the loudspeaker.