System for Updating the Program Code of STM32 Microcontrollers Based on a Composite USB Device

The system was designed using the STM32CubeIDE development environment and the STM32CubeMX visual configurator. With their help, you can quickly and conveniently manage the configuration, debug the program code and write the firmware to the microcontroller's memory. The main provisions of the USB standard were studied, based on which a composite USB device consisting of two classes (CDC and MSC) was implemented. For cryptographic data protection, the AES-128 block encryption algorithm, optimal for the microcontroller, was selected. It is used to encrypt the program transferred by the user to the memory of the microcontroller and decrypt it during the download process. With the help of Option bytes, additional memory protection from reading was implemented both when connected using a programmer and via USB. Finally, the operation of the entire system was tested. With the help of test “firmware”, the correct operation of the USB bootloader was checked.