Engineer Details Secure BLE Firmware Update Architecture for Nordic nRF5340

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A developer has published architecture notes from an internal R&D project exploring secure over-the-air firmware updates on the Nordic nRF5340-DK development board using Bluetooth Low Energy. The system uses Zephyr RTOS, nRF Connect SDK, MCUmgr SMP for transport, and MCUboot for verified boot, allowing a technician to update field devices locally without requiring cloud or internet connectivity. Firmware images are signed with ECDSA P-256 and verified by MCUboot before execution, ensuring an unauthorized binary cannot be run even if a BLE connection is established. The update flow separates three distinct states — image transferred, image allowed to boot, and image confirmed healthy — so that if a new firmware fails its startup checks, MCUboot automatically restores the previous working image on the next reboot. A timed service mode further limits maintenance access to a defined window, keeping update control at the device level rather than relying solely on the operator dashboard.

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