Factory-pairing two nRF52840

[mlac]

Hi there,

I'm developing a product composed of two nRF52840, one being a USB+BLE keyboard and the other being a wireless USB dongle. The two are connected via Nordic UART Service.

I want to pre-pair the keyboard and dongle in the factory via USB. I already store the keyboard's address in the dongle via the settings API and vice versa, which works as intended. But I also want to ensure secure communication.

By secure communication, I'm not even sure which security level I should use, but I'd expect the pre-pairing process to fill out the relevant bt/* Settings API values so that the keyboard and dongle get securely connected.

Please give me some directions regarding the implementation details because I'm quite lost.

Thanks in advance!
- Laci

[Kenneth]

Hello,

If you want to ensure two devices (or a family of devices) are the ones only able to bond. Then I recommend to check out OOB, normally OOB is used over NFC, but there is nothing preventing you to store a 16byte OOB key in produciton, and use this OOB key to ensure only those two devices you control can successfully bond and exchange information.

I suggest to for instance look at the auth_oob_data_request() in main.c for peripheral_keyboard  and replace app_nfc_oob_data_get() with the 128-bit key you want to use. Similar on central you need to add the .oob_data_request callback in conn_auth_callbacks to handle such event. I believe you can use this example as starting point for central:
https://developer.nordicsemi.com/nRF_Connect_SDK/doc/latest/nrf/samples/bluetooth/central_hids/README.html 

Similar for keyboard:
https://developer.nordicsemi.com/nRF_Connect_SDK/doc/latest/nrf/samples/bluetooth/peripheral_hids_keyboard/README.html#peripheral-hids-keyboard 

Kenneth