RE: Re-pairing NRF BLE with the same host without manual bond erase button pushing

Olli — Fri, 14 Oct 2016 06:38:39 GMT

Great, this worked!

I inserted there a small safety condition that if at least NN hours have elapsed since previous communication, then the NRF device agrees to pair again with the same host, to allow re-pairing yet avoid possibility that other malicious host mimicking the same Mac would attempt to steal the bonded connection from the actual authorized host.

Many thanks also for the quick reply: Support in this forum is awesome, I've discovered answers to dozens of my earlier questions by searching Q&As in this forum!

RE: Re-pairing NRF BLE with the same host without manual bond erase button pushing

FormerMember — Tue, 11 Oct 2016 13:08:27 GMT

The peer_manager code is set up so that it will reject a new bonding procedure from devices with already stored bonding information.

Starting from the first received event in the pairing process, BLE_GAP_EVT_SEC_PARAMS_REQUEST, the piece of code that rejects the new bonding process can be found the following way:

BLE_GAP_EVT_SEC_PARAMS_REQUEST --> security_dispatcher.c:

smd_ble_evt_handler( --> BLE_GAP_EVT_SEC_PARAMS_REQUEST --> sec_params_request_process)

-->

sec_params_request_process(--> SMD_EVT_PARAMS_REQ)

-->

smd_evt_handler( --> SMD_EVT_PARAMS_REQ --> smd_params_reply_perform(..))

In smd_params_reply_perform(..) there is a check if the connected device already is bonded. And if it is already bonded, the pairing procedure will be rejected:

static void smd_params_reply_perform(uint16_t conn_handle)
{
ret_code_t err_code;

if (  (ble_conn_state_role(conn_handle) == BLE_GAP_ROLE_PERIPH)
    && im_peer_id_get_by_conn_handle(conn_handle) != PM_PEER_ID_INVALID)
{
    // Bond already exists. Reject the pairing request if the user doesn't intervene.
    ble_conn_state_user_flag_set(conn_handle, m_sm.flag_id_reject_pairing, true);
    send_config_req(conn_handle);
}
else
{
    ble_conn_state_user_flag_set(conn_handle, m_sm.flag_id_reject_pairing, false);
}
....