A system and method updates software in a mobile device, which includes an application processor and associated application processor memory and a radio processor and associated radio processor memory and a serial port connecting the processors. The associated application processor memory stores an "n" byte digest signature that had been calculated. The software in the radio processor and associated radio processor memory can be updated by over-the-air software loading while checking the associated application processor memory for the "n" byte digest signature used for the over-the-air software loading.