Hardware: S32K144EVB-Q100
Software: S32 Design Studio, OpenBLT Bootloader, an5401-csec
We intend to protect only the bootloader using BOOT_DEFINE (16KB protected) and want the bootloader to verify the application MAC on every reset to establish a proper chain of trust.
We currently have a hardcoded CMAC value that we store and verify upon every reset as a proof of concept.
After bootloader verification (BOK=1), we need to verify application on every reset. For this, we need to:
- Store application MAC somewhere during programming
- Verify application MAC on every reset
We've considered these options but have concerns:
- CSEc KEY slots (like KEY_2): Can't read back stored keys due to SHE protocol security - keys are write-only. How can we retrieve MAC for comparison?
- Flash memory: Not suitable because application area gets erased when new application is programmed, so stored MAC would be lost.
- EEPROM: Is this a good approach? Any recommended EEPROM addresses?
What other approaches would be suitable for storing application MAC that bootloader can reliably read for verification on every reset?
