Difference between two LTKs

[strengthstrong]

During the pairing phase, LTK will be generated for the secure connect, and no LTK will be generated for the legacy pair, but LTK will be generated for the subsequent bonding. Is the LTK generated during the pairing phase the same as the LTK during the bonding phase? If not, then how does secure connect generate LTK for bonding

[Kenneth]

Hi,

There is no short answer here, but we follow the Bluetooth core specification, so please refer to Bluetooth core specification for the various security procedures and phases.

In addition you can find some message sequence charts for the softdevices on which events are generated during the various security procedures here:
https://infocenter.nordicsemi.com/topic/com.nordic.infocenter.s132.api.v7.0.1/group___b_l_e___g_a_p___p_e_r_i_p_h___s_e_c___m_s_c.html 

Best regards,
Kenneth

[randy]

Hi Kenneth,

I'm also interested in this procedure. from the message chart, it didn't elaborate on how to get LTK in the legacy pairing. Could you use legacy passkey entry pairing as an example to show the detail?

Thanks,

Randy

[Kenneth]

Hi,

https://infocenter.nordicsemi.com/topic/com.nordic.infocenter.s132.api.v7.0.1/group___b_l_e___g_a_p___p_e_r_i_p_h___b_o_n_d_i_n_g___p_k___c_e_n_t_r_a_l___o_o_b___m_s_c.html

When the application reply with the sd_ble_gap_sec_params_reply() on BLE_GAP_EVT_SEC_PARAMS_REQ it provide a pointer to ble_gap_sec_keyset_t, now later when you get an BLE_GAP_EVT_AUTH_STATUS you can read out the LTK from the previously supplied ble_gap_sec_keyset_t.

Best regards,
Kenneth