ST Controller Requirement with Secure Boot

[PMeth.2]

We are working on one of the project there is a requirements to develop small adaptor card to support new external module with I2C interface (Current Host module support only SPI interface).

We are looking for low cost basic Microcontroller from ST for SPI to I2C conversion as mentioned below;

1. Microcontroller shall have secure boot –>Secure Element (Secure memory + first stage bootloader)
2. Integrity of the Application FW shall be checked before boot.
3. Microcontroller shall be upgradable with an encrypted firmware image (Second stage bootloader) through SPI.
4. Integrity of the upgradable Image shall be checked .

[Peter BENSCH]

Welcome, @Community member​, to the community!

Two STM32 families currently fit: STM32U5 and STM32L5, both based on Cortex-M33 and providing TrustZone. Suitable and low cost types could be the STM32L552CC or the STM32L562CE (with AES encryption), which meet all requirements. There is also the software package X-CUBE-SBSFU available to speed up your development process.

Does it answer your questions?

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/Peter

[Pavel A.]

> We are looking for low cost basic Microcontroller 

Before you proceed with this, are you aware of the global shortage of microcontroller parts?

Check with your buyer what is available to purchase.

STM32L5 and U5 mentioned by Peter are new, high demand parts, and not exactly 'basic'.

If you can change the requirement from "secure boot & secure element" to something like:

"Firmware will be preloaded by trusted factory, locked down and not readable from outside"

then the selection of low cost STM32 models is much wider.

Even STM8s can act as SPI to I2C converter.

If you can reduce/reject the requirement #3 (for example, instead of in-system firmware image update of the converter,

update only some data or parameters, or replace the whole pre-programmed chip) it will be even easier.