Network Key Update

1. Summary

In order to make sure that every device doesn't reach the maximum value of the frame counter, the TC need to perform a NWK key update. This update should be done periodically at long intervals. The case of SED is very specific. For example, if a SED is the sleep state, it is not going to receive any message and therefore miss the NWK key Update. It then needs to perform a rejoin to the NWK.

2. Gecko SDK version

Gecko SDK Suite 4.1.0 or later

3. Hardware Required

• 3x Wireless Starter Kit Main Board
• 3x BRD4180A

4. Connections Required

Connect the radio boards to the WSTK mainboards. Connect your desired gateway device via serial connection to a computer.

5. Running the Applications

Build and flash the nwkKeyUpdate_CO application to one board (coordinator). Build and flash the nwkKeyUpdate_Ro application to another one (Router). Build and flash the nwkKeyUpdate_SED application to the last one (SED).

Using the Application

• Form the network on the coordinator by sending form through the serial.
• If you want to capture packets, use keys print to get the NWK key and add it to your keys.
• Use open to Open the network
• Send join to both the Router and SED to allow them to join the network
• On the Coordinator (TC), send updateNwk in order to update the key when your 2 devices joined the network

Interpretation

After doing the whole process, it is possible to see that the Trust Center and the router updated their NWK key.
Before the NWK Key Update on the TC
After the NWK Key Update on the TC

After the NWK Key Update on the SED

From what we can see, the SED missed the NWK Update. It will need to perform a rejoin process in order to get the NWK Key.

6. Traces & other documents

This directory also contains trace captures on Network Analyzer and Wireshark directly in the repositories

• trace_nwk_key_update.isd : Capture for NA
• trace_nwk_key_update.pcapng : Capture for Wireshark

To use Wireshark Capture You need to add the well-known key to your wireshark keys to decode packets.
Go to : [Edit -> Preferences -> Protocols -> ZigBee -> Edit] and add : 5A:69:67:42:65:65:41:6C:6C:69:61:6E:63:65:30:39 as the well-known key\

To get more informations : AN1233: Zigbee Security
UG391: Zigbee Application Framework dev guide