DTLS on SAM R21 Xplained Pro: Guide/Demo

Summary

This article supplies the instructions to setup a DTLS connection demonstration by using RIOT-OS and the WolfSSL DTLS example provided by RIOT-OS. The first part guides the user in setting up two SAM R21 Xplained Pro microcontrollers using the example application to connect using DTLS. The second part guides the user in setting up virtual boards in RIOT. This is done to make capturing the DTLS packets possible.

Requirements

You must have followed the Riot-OS Setup step 1, 2 and 3 before using this guide. It is assumed that RIOT-OS is installed to ~/RIOT/.

• Operating system: Ubuntu 24.04 (Guide was created running a VM on Oracle VirtualBox 6.1)
• Packages: git python3

Description

Step 1

This step is an addition to the Riot-OS Setup.

• Update your packages if you have not already done this.

sudo apt-get update

• Install the pyudev package

sudo apt-get install python3-pyudev 

• Find out the serial numbers of your SAM R21 XPro devices and note them for later use

make list-ttys

• Open two additional terminals and connect to both devices by using their ttys. (Adjust the code if your ttys differ)

cd RIOT/dist/tools/pyterm
./pyterm -p /dev/ttyACM0
./pyterm -p /dev/ttyACM1

Step 2

Build the application and flash it on both devices.

• Navigate to the folder containing the WolfSSL DTLS example in RIOT and build the application

cd RIOT/examples/dtls-wolfssl
make BOARD=samr21-xpro

• Flash the newly built application onto both devices using their serial numbers

make BOARD=samr21-xpro SERIAL="ATML21270318xxxxxxx" flash
make BOARD=samr21-xpro SERIAL="ATML21270318xxxxxxx" flash

• The example application is now running on both devices. Use command help to show the available options

WolfSSL DTLS Example Help Menu

Step 3

Use the applications to setup a DTLS connection

• Use ifconfig on the device that is designated as the server and note the IPv6 address
• Start the DTLS Server

dtlss

• Use the DTLS Client to start the connection test

dtlsc IPv6-server-address

WolfSSL DTLS Example successful Connection

Capturing DTLS Traffic

If you want to capture and analyze the DTLS the packets using a packet sniffer, e.g. Wireshark, you have to use RIOT native boards. SAM R21 XPro devices are not powerful enough to support packet capture with Wireshark on their own.

Wireshark Setup

Follow the steps to install Wireshark on Ubuntu 24.04, if necessary:

• Install Wireshark

sudo apt install wireshark

• When asked if non-superusers should be able to catpure packets answer "Yes".
• Add user to the wireshark group to make capture possible

sudo usermod -a -G wireshark "$USER"

• Check if the wireshark group is present for your user

groups $USER

Step 1

Setup a virtual network for RIOT instances by using the Tapsetup tool.

• Navigate to the Tapsetup tool and create two virtual network taps and a virtual bridge

cd ~
cd RIOT/dist/tools/tapsetup
sudo ./tapsetup --create 2

• Build dtls-wolfdtls for RIOT native boards

cd ~
cd RIOT/examples/dtls-wolfssl
make all

• Setup the first virtual RIOT board

PORT=tap0 make term

• Setup the second virtual RIOT board using a second terminal

cd RIOT/examples/dtls-wolfssl
PORT=tap1 make term

Step 2

Configure Wireshark to capture packets on either tap0, tap1 or tapbr0 (Bridge). This depends on which view is more interesting to you. In the following steps tap1 is used for capturing packets.

• Start Wireshark and set it to capture packets on interface tap1
• Use the applications to setup a DTLS connection. First use ifconfig and note the IPv6 address of the designated server application. Then use the following commands to setup the connection:

dtlss
dtlsc IPv6-server-address

Step 3

Analyze the captured traffic in Wireshark

WolfSSL DTLS Example Wireshark Capture

Used Hardware

• 2x Atmel SAM R21 Xplained Pro
• Connective cables (Micro USB B)

Courses

• Riot-OS Setup

References

• https://www.riot-os.org/
• https://www.wolfssl.com/