nRF52 BLE improvements

Bluetooth.h

@@ -387,10 +387,36 @@ char bt_devname[11];
     bt_ssp_pin = 0;
     bt_state = BT_STATE_ON;
   }
-
 void bt_pairing_complete(uint16_t conn_handle, uint8_t auth_status) {
     if (auth_status == BLE_GAP_SEC_STATUS_SUCCESS) {
+      BLEConnection* connection = Bluefruit.Connection(conn_handle);
+
+      ble_gap_conn_sec_mode_t security = connection->getSecureMode();
+
+      // On the NRF52 it is not possible with the Arduino library to reject
+      // requests from devices with no IO capabilities, which would allow
+      // bypassing pin entry through pairing using the "just works" mode.
+      // Therefore, we must check the security level of the connection after
+      // pairing to ensure "just works" has not been used. If it has, we need
+      // to disconnect, unpair and delete any bonding information immediately.
+      // Settings on the SerialBT service should prevent unauthorised access to
+      // the serial port anyway, but this is still wise to do regardless.
+      //
+      // Note: It may be nice to have this done in the BLESecurity class in the
+      // future, but as it stands right now I'd have to fork the BSP to do
+      // that, which I don't fancy doing. Impact on security is likely minimal.
+      // Requires investigation.
+
+      if (security.sm == 1 && security.lv >= 3) {
+          bt_state = BT_STATE_CONNECTED;
+          cable_state = CABLE_STATE_DISCONNECTED;
           bt_disable_pairing();
+      } else {
+          if (connection->bonded()) {
+              connection->removeBondKey();
+          }
+          connection->disconnect();
+      }
     } else {
       bt_ssp_pin = 0;
     }
@@ -402,22 +428,27 @@ char bt_devname[11];
         bt_ssp_pin += ((int)passkey[i] - 48) * pow(10, 5-i);
     }
     kiss_indicate_btpin();
-      if (match_request) {
     if (bt_allow_pairing) {
         return true;
     }
-      }
     return false;
 }
 
 void bt_connect_callback(uint16_t conn_handle) {
     bt_state = BT_STATE_CONNECTED;
     cable_state = CABLE_STATE_DISCONNECTED;
+
+    //BLEConnection* conn = Bluefruit.Connection(conn_handle);
+    conn->requestPHY(BLE_GAP_PHY_2MBPS);
+    conn->requestMtuExchange(512+3);
+    conn->requestDataLengthUpdate();
 }
 
 void bt_disconnect_callback(uint16_t conn_handle, uint8_t reason) {
+    if (reason != BLE_GAP_SEC_STATUS_SUCCESS) {
         bt_state = BT_STATE_ON;
     }
+}
 
 bool bt_setup_hw() {
   if (!bt_ready) {
@@ -433,12 +464,19 @@ char bt_devname[11];
     Bluefruit.configPrphBandwidth(BANDWIDTH_MAX);
     Bluefruit.autoConnLed(false);
     if (Bluefruit.begin()) {
-        Bluefruit.setTxPower(4);    // Check bluefruit.h for supported values
+      Bluefruit.setTxPower(8);    // Check bluefruit.h for supported values
-        Bluefruit.Security.setIOCaps(true, true, false);
+      Bluefruit.Security.setIOCaps(true, false, false); // display, yes; yes / no, no; keyboard, no
+      // This device is indeed capable of yes / no through the pairing mode
+      // being set, but I have chosen to set it thus to force the input of the
+      // pin on the device initiating the pairing.
+
+      Bluefruit.Security.setMITM(true);
       Bluefruit.Security.setPairPasskeyCallback(bt_passkey_callback);
-        Bluefruit.Periph.setConnectCallback(bt_connect_callback);
+      Bluefruit.Security.setSecuredCallback(bt_connect_callback);
       Bluefruit.Periph.setDisconnectCallback(bt_disconnect_callback);
       Bluefruit.Security.setPairCompleteCallback(bt_pairing_complete);
+      //Bluefruit.Periph.setConnInterval(6, 12); // 7.5 - 15 ms
+
       const ble_gap_addr_t gap_addr = Bluefruit.getAddr();
       char *data = (char*)malloc(BT_DEV_ADDR_LEN+1);
       for (int i = 0; i < BT_DEV_ADDR_LEN; i++) {
@@ -469,11 +507,13 @@ char bt_devname[11];
     // start device information service
     bledis.begin();
 
+    SerialBT.bufferTXD(true); // enable buffering
+
+    SerialBT.setPermission(SECMODE_ENC_WITH_MITM, SECMODE_ENC_WITH_MITM); // enable encryption for BLE serial
     SerialBT.begin();
 
     blebas.begin();
 
-      // non-connectable advertising
     Bluefruit.Advertising.addFlags(BLE_GAP_ADV_FLAGS_LE_ONLY_GENERAL_DISC_MODE);
     Bluefruit.Advertising.addTxPower();
 

Config.h

@@ -189,6 +189,7 @@
     bool device_init_done = false;
     bool eeprom_ok = false;
     bool firmware_update_mode = false;
+    bool serial_in_frame = false;
 
 	// Boot flags
 	#define START_FROM_BOOTLOADER 0x01

Utilities.h

@@ -668,6 +668,19 @@ void serial_write(uint8_t byte) {
 			Serial.write(byte);
 		} else {
 			SerialBT.write(byte);
+
+            #if MCU_VARIANT == MCU_NRF52 && HAS_BLE
+            // This ensures that the TX buffer is flushed after a frame is queued in serial.
+            // serial_in_frame is used to ensure that the flush only happens at the end of the frame
+            if (serial_in_frame && byte == FEND) {
+                SerialBT.flushTXD();
+                serial_in_frame = false;
+            }
+            else if (!serial_in_frame && byte == FEND) {
+                serial_in_frame = true;
+            }
+            #endif
+
 		}
 	#else
 		Serial.write(byte);