Firmware protection unit of microcontroller with on-chip flash memory and protection method

The invention discloses a firmware protection unit of a microcontroller. The firmware protection unit of the microcontroller comprises a firmware bag and a Bootloader, wherein the firmware bag and the Bootloader are publicly issued; the public firmware bag is composed of an encrypted guide block and a firmware after being encrypted; the encrypted guide block comprises information of encrypted local area of the firmware, and the information comprises offset and length and is used for orientating a ciphertext area when decoding; the encrypted guide block further comprises a random number with 16 bytes, and the random number is used for producing a practical working secret key; a protection method specifically comprises the steps of firstly conducting encryption on part of the firmware, wherein different secret keys are used to conduct encryption during the encryption of each time; then starting a loading program Bootloader, carrying out one machine one recognition code starting, upgrading a decoding firmware, a