What is the reason for BLE_GAP_SEC_STATUS_DHKEY_FAILURE

[Youssif]

Hi

I am writing an app to utilise the new LESC feature using Diffie Hellman related pairing. I am testing the app against the Nordic provided ble_app_multirole_lesc. I have tried to mimic the app on my end as much as possible, including setting the IO capability to BLE_GAP_IO_CAPS_DISPLAY_YESNO. However, when I try to pair from my device using my app, I eventually get the error BLE_GAP_SEC_STATUS_DHKEY_FAILURE. This happens after I get the event BLE_GAP_EVT_LESC_DHKEY_REQUEST, and I successfully reply with sd_ble_gap_lesc_dhkey_reply(p_dhkey). So I would like to know the reason for this error. Is it related to the keys being generated or is it more related to the sequence of operations, or is it something else entirely?

I am using softdevice version 2.0.0 and SDK version 11.0.0.

[Pål Håland]

I guess it is this example you are using? ble_sdk_app_multirole_lesc

The examples is based on numeric comparison, and both devices will have to have display for it to work (DISPLAY YES NO/keyboard)

peripheral numeric comparison

central numeric comparison

When you get the BLE_GAP_EVT_DHKEY_REQUEST you should compute the dhkey, when you get the BLE_GAP_EVT_PASSKEY_DISPLAY then you reply first with sd_ble_gap_auth_key_reply and then right after sd_ble_gap_lesc_dhkey_reply

If you use keyboard on one side, then it is a different sequence, and you would have to adjust your code to match those MSC.

[Youssif]

Thanks Pal. But this doesn't answer my question, which is "What is the reason for "BLE_GAP_SEC_STATUS_DHKEY_FAILURE". The sequence you suggest is exactly what I am doing. Yet I am still getting this error message. In my example I am using the numeric comparison on both ends.

[Pål Håland]

For getting a answer on what the reason is you would have to provide a more detailed question with code snippets or sniffer logs.

There is only once place the SoftDevice generate this code, and that is when it validates the received DHKEY during the procedure. It would help with some sniffer logs to see witch device is generating the error code.

[Youssif]

Thanks Pal. I just wanted to know the general reason and this answers my question.