Hi, I have done the bonding and saving context to flash. As an example I used ble_app_template. I cutted all redundant code and limited to single bond for simplicity. In my code I save next:
- m_connection_table (I changed it a little bit)
- m_peer_table
- m_bond_table (i.e. ble_gap_enc_key_t, LTK)
At device startup I load m_peer_table to know what peer address I'm waiting to connect.
Advertice
Than after peer connect I load m_bond_table with presaved LTK.
At BLE_GAP_EVT_SEC_PARAMS_REQUEST peer central gives:
ble_evt->evt.gap_evt.params.sec_params_request.peer_params.kdist_periph.enc - 1
ble_evt->evt.gap_evt.params.sec_params_request.peer_params.kdist_central.id - 0
ble_evt->evt.gap_evt.params.sec_params_request.peer_params.kdist_periph.sign - 1
ble_evt->evt.gap_evt.params.sec_params_request.peer_params.bond - 1
My local setup is
m_sec_params.kdist_periph.enc = 1;
m_sec_params.kdist_periph.id = 0;
m_sec_params.kdist_periph.sign = 0; //Not supported yet
At BLE_GAP_EVT_CONN_SEC_UPDATE
Established Mode 0x01, Level 0x02 - so link is encrpted.Here I apply service context.
At BLE_GAP_EVT_AUTH_STATUS if bond successfull I save context to nonvolatile memory. But here the LTK is different whan I sent as reply to BLE_GAP_EVT_SEC_PARAMS_REQUEST.
After host disconnected I save all context similar to at BLE_GAP_EVT_AUTH_STATUS event.
As I understand LTK have to be constant for long time, so why it changes at each reconnection? It seem that I repeat bonding procedure each time at connection because I do not receive BLE_GAP_EVT_SEC_INFO_REQUEST at reconnect as stated here [https://devzone.nordicsemi.com/documentation/nrf51/4.4.0/html/group___b_o_n_d_e_d___m_a_s_t_e_r.html] or here [https://devzone.nordicsemi.com/documentation/nrf51/6.0.0/s110/html/a00824.html]
