Abstract: Process for confirming transactions by means of mobile units (MU), wherein a control device (CD) sends a request message (RM) containing transaction data (TD) to a mobile unit (MU), which can send to the control device (CD) a confirmation message (CM) containing a confirmation code (CD), wherein the control device (CD) and/or the mobile unit (MU) are provided with one or more digital memories (DM) in which security applications (SA) are stored for encoding and digitally signing the request message (RM) and/or the confirmation message (CM), respectively, before sending them. The present invention also relates to a system for carrying out said process.