STM32 MCUs secure firmware install (SFI)

STM32 SFI is a solution for secure manufacturing in production environments that guarantees the authenticity, integrity, and confidentiality of the firmware. It is available on select STM32L4, and most STM32L5, STM32U5, STM32H5 and STM32H7 microcontrollers.

Instructions

The procedure consists of two main steps:

1. Preparation of files and Hardware Secure Module (HSM) using the source code and the toolkit provided by STMicroelectronics. Two elements are necessary to perform an SFI sequence using FlashPro-ARM/GangPro-ARM

   • Encrypted firmware binary in a SFI file (*.sfi)

   • STM32HSM programmed module

2. Programming of the target’s flash memory and option bytes using FlashPro-ARM/GangPro-ARM using the files prepared in the first step.

1. Preparing necessary files:

1. Preparation of the Encryption key and Encryption nonce files (AES128Key.bin and Nonce.bin) - both files can be generated using STM32TrustedPackageCreator (SFI tab). To generate Encryption nonce file and Encryption key file, proceed as follows:

   • Open Trusted Package Creator and select SFI

   • Open SFI tab

   • Press “Generate” buttons(red arrows) and set destination place for generated files

Open

2. Preparation of Option Bytes Config file (OptionBytesSetting.csv) - file can be generated using STM32TrustedPackageCreator (SFI Option Bytes tab).
   To generate Option Bytes Config file file, proceed as follows:

   • Open Trusted Package Creator and select SFI

   • Open SFI Option Bytes tab

   • Select target microcontroller

   • In window set finall option bytes configuration after secure firmware install operation

   • Press “Open Option Bytes File” button and set destination place for generated file

Open

3. Preparation of firmware files (firmware.bin, .hex, .srec, etc.)

4. Preparation of an encrypted firmware binary file (*.sfi) using STM32TrustedPackageCreator (SFI tab) or STM32TrustedPackageCreator_CLI (-sfi option), keys, option bytes config file and input firmware are necessary in this step.

5. Programming HSM modules with a limited number of licenses using STM32TrustedPackageCreator (HSM tab) or STM32TrustedPackageCreator_CLI (-hsm option), keys (AES128Key.bin and Nonce.bin) are necessary in this step and they must be the same as for firmware encryption.

2. Programming flash memory and option bytes using FlashPro-ARM/GangPro-ARM on Windows

Configuration for FlashPro-ARM and GangPro-ARM is the same, but GangPro-ARM can program up to 6 device simultaneously.

1. Open FlashPro-ARM/GangPro-ARM software

2. Open Setup → SFI Setup window

   1. Set HSM card index(by default 1)

   2. Check “Enable” box

   3. Use “Browse” button and pick *.sfi file, generated by STM32TrustedPackageCreator

   4. Check “Set log file path” box only if you would like to save used licenses from HSM module (using saved licenses allows reprogramming of the same DUT without using HSM quota)

   5. Use “Browse” button and set place where log file with licenses should be saved

   6. Press “Ok” button to save SFI setup

3. Press “AUTO PROG.”(or “WRITE FLASH”) button to execute secure firmware install operation

4. Check output logs after AutoProgram

   1. FlashPro-ARM

      Communication initialization......... OK OSC=48.15 MHz, Sys.CLK=48.15 MHz Erasing memory ............................... done Secure firmware install procedure start... OK Communication initialization................... OK Reading MCU decriptor......................... OK Option bytes setup................................. OK Certificate analyze................................. OK Request HSM license............................ OK Firmware install...................................... OK RSS version = 1.4.0.............................. OK RSSe version = 2.3.0............................ OK Install license......................................... OK Processing Image Header..................... OK SFI programming.................................... OK Warning: Could not verify security state after last chunk programming -------- D O N E --- ( run time = 10.7 sec.)

   2. GangPro-ARM

Useful links

STMicroelectronics application notes and user manuals:

[1] AN5054 - Secure programming using STM32CubeProgrammer

[2] AN4992- STM32 MCUs secure firmware install (SFI) overview

[3] AN5156 - Introduction to STM32 microcontrollers security

[4] UM2238 - STM32 Trusted Package Creator tool software description