Add simple step for securing Zigbee network (#899)

* Add simple step for securing zigbee network

* Update configuration.md

* Update how_to_secure_network.md

* Update index.md

docs/configuration/configuration.md

@@ -7,7 +7,8 @@ The values shown are the default ones.
 # Required: Home Assistant integration (MQTT discovery)
 homeassistant: false
 
-# Required: allow new devices to join
+# Required: allow new devices to join.
+# WARNING: Disable this after all devices have been paired!
 permit_join: true
 
 # Required: MQTT settings
@@ -53,4 +54,4 @@ advanced:
   rtscts: true
   # Optional: soft reset ZNP after timeout (in seconds); 0 is disabled
   soft_reset_timeout: 0
-```
+```

docs/getting_started/pairing_devices.md

@@ -1,4 +1,5 @@
 **IMPORTANT:** Before you start, make sure that `permit_join: true` is set in your `configuration.yaml`. Otherwise new devices cannot join the network!
+It's equally important that `permit_join: false` is set in your `configuration.yaml` after initial setup is done to keep your Zigbee network safe and to avoid accidental joining of other Zigbee devices.
 
 Start by checking if your Zigbee device is supported, see  [Supported devices](../information/supported_devices.md).
 
@@ -65,4 +66,4 @@ Factory reset by:
 (at the 3rd, the 10th, and the 15th second).
 - After releasing the Binding Key, press the Switch Key within 2 seconds. The network indicator
 will rapidly flash green.
-- After fast flashes, Z809A will reboot, and the restore is completed. The socket will automatically connect now.
+- After fast flashes, Z809A will reboot, and the restore is completed. The socket will automatically connect now.

docs/how_tos/how_to_secure_network.md

@@ -0,0 +1,16 @@
+# How to secure your Zigbee network
+By default your Zigbee network isn't as secured as possible. The following settings are recommeded to apply to your configuration.
+
+## Disabled joining
+To disable joining it's important that `permit_join: false` is set in your `configuration.yaml`.
+
+## Change Zigbee network encryption key
+**Changing the key requires repairing of all devices!**
+
+Zigbee2mqtt uses a default encryption key. Therefore it is recommended to use a different one.  To use a different encryption key add the following to you `configuration.yaml`:
+
+**Do not use the following key.**
+```
+advanced:
+  network_key: [7, 3, 5, 7, 9, 11, 13, 15, 0, 2, 4, 6, 8, 11, 12, 13],
+```

docs/index.md

@@ -25,6 +25,7 @@ Welcome to the Zigbee2mqtt documentation!
 * [How to support new devices](how_tos/how_to_support_new_devices.md)
 * [How to debug](how_tos/how_to_debug.md)
 * [How to support new devices on Hass.io](how_tos/how_to_support_new_devices_on_hassio.md)
+* [How to secure your Zigbee network](how_tos/how_to_secure_network.md)
 
 ### Information
 * [Supported devices](information/supported_devices.md)