RE: How do you check "App completes DHKey calculation"?

Einar Thorsrud — Tue, 12 Oct 2021 11:57:15 GMT

Hi,

Referring to the ble_app_multirole_lesc example in SDK 13 this happens in the handling of the BLE_GAP_EVT_LESC_DHKEY_REQUEST event.

        case BLE_GAP_EVT_LESC_DHKEY_REQUEST:
            NRF_LOG_INFO("%s: BLE_GAP_EVT_LESC_DHKEY_REQUEST\r\n", nrf_log_push(roles_str[role]));

            static nrf_value_length_t peer_public_key_raw = {0};

            peer_public_key_raw.p_value = &p_ble_evt->evt.gap_evt.params.lesc_dhkey_request.p_pk_peer->pk[0];
            peer_public_key_raw.length = BLE_GAP_LESC_P256_PK_LEN;

            err_code = nrf_crypto_ecc_public_key_from_raw(NRF_CRYPTO_BLE_ECDH_CURVE_INFO,
                                                          &peer_public_key_raw,
                                                          &m_peer_public_key);
            APP_ERROR_CHECK(err_code);

            err_code = nrf_crypto_ecdh_shared_secret_compute(NRF_CRYPTO_BLE_ECDH_CURVE_INFO,
                                                            &m_private_key,
                                                            &m_peer_public_key,
                                                            &m_dh_key);
            APP_ERROR_CHECK(err_code);

            err_code = sd_ble_gap_lesc_dhkey_reply(conn_handle, &m_lesc_dh_key);
            APP_ERROR_CHECK(err_code);
            break;

Do you miss this in your implementation?

By the way, note that this was changed in later SDK versions as it is a time consuming operation, and it makes sense to do this in the main loop rather than in an interrupt (which is the case in the SDK 13 example).