Abstract: The present invention relates to a method for authenticating a user (Ui) requesting a transaction with a service provider (SP), which comprises: using authentication data (dauth) read on a screen by means of a mobile terminal (TEL) to generate (E) an authorisation code (cod.) that is specific to the user and to the requested transaction; reading (F) the authorisation code, displayed by the mobile terminal, using a reading means of a digital device (PC); and sending (G) the read authorisation code from said digital device to the service provider in order to authenticate the user.