Secure BLE OTA Firmware Updates on nRF5340: Architecture Notes

Short summary

An internal R&D project documenting a secure BLE OTA firmware update architecture on the Nordic nRF5340-DK using Zephyr, MCUmgr SMP, and MCUboot. The design separates transfer, boot-allowance, and health-confirmation into distinct states enabling automatic rollback to known-good images. Firmware is signed with ECDSA P-256, downgrade prevention is enforced, and maintenance access is time-limited. The key lesson: OTA is a system feature where all components must agree on failure states.

• •Three-state model: transferred, allowed-to-boot, confirmed-healthy — enables automatic rollback
• •ECDSA P-256 signing and downgrade prevention enforced on-device, not just in dashboard
• •BLE provides local maintenance channel without cloud dependency for field-deployed devices

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