SFIx

Coming soon

1. What is SFIX

OEM product can embed external Flash additionally to STM32 internal Flash.
The SFIX solution provides security when programming STM32 devices and external Flash in a non-trusted facility owned by a Contract Manufacturer (CM).
The SFIX solution is the same solution than the SFI solution, it also allows the external Flash programming.

Information

For detailed on SFIX, please refer to AN4992 STM32 MCUs secure firmware install (SFI) overview

2. External flash memory programming principle

The OEM external flash content must be encrypted to ensure the OEM data confidentiality.

External flash crypto is handled by the OTFDEC peripheral. This peripheral can encrypt and decrypt on-the-fly external firmware and data stored in external flash memory connected to STM32 microcontrollers through the OCTOSPI interface. The OTFDEC can handle up to 4 regions of external flash memory, each one with its own dedicated Key. The OTFDEC uses standard AES CTR 128-bit algorithm for encryption and decryption operations. Refer to the OTFDEC section of the STM32 microcontroller reference manual to get more insight.

The SFIX cannot handle internal flash memory in a first sequence and external in a separate independent one: when SFIX handles external firmware, it must first handle internal firmware that in turn enable the decryption at runtime of the external firmware. The internal flash firmware must enable the read/fetch of data/code within the external flash memory, using the OTFDEC and the OCTOSPI peripherals.