MQTT

MQTT (Message Queuing Telemetry Transport) is a lightweight messaging protocol that plays a vital role in automotive applications. It is widely used for:

• Vehicle Telemetry: MQTT efficiently transmits real-time data such as speed, location, fuel level, and engine performance from vehicles to central servers for monitoring and analysis.

• Fleet Management: It enables communication between fleet vehicles and management systems, improving route optimization, resource allocation, and maintenance scheduling.

• Remote Diagnostics and Updates: It facilitates remote diagnostics and software updates for vehicles, reducing downtime and maintaining system efficiency.

Overall, MQTT's lightweight nature and efficient communication capabilities make it ideal for the automotive industry, where reliable data exchange is critical.

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Mosquitto Clients Complete Guide

Let's start with the fundamental commands for publishing and subscribing. The mosquitto-clients package provides two main tools: mosquitto_pub for publishing messages and mosquitto_sub for subscribing to topics.

Basic Publishing (mosquitto_pub)

The simplest form of publishing a message:

# Publish a single message to a topic
mosquitto_pub -h localhost -t "test/topic" -m "Hello, AutoSecurityy!"

# Publish with quality of service (QoS) level 1
mosquitto_pub -h localhost -t "test/topic" -m "Important message" -q 1

# Publish retained message (stays active on broker)
mosquitto_pub -h localhost -t "test/status" -m "device_online" -r

# Publish null message (useful for clearing retained messages)
mosquitto_pub -h localhost -t "test/topic" -n -r

# Publish from a file
mosquitto_pub -h localhost -t "test/topic" -f message.txt

# Publish JSON data
mosquitto_pub -h localhost -t "test/data" -m '{"sensor": "temp", "value": 25.1}'

# Publish binary data (hex)
mosquitto_pub -h localhost -t "test/binary" -m $'\x41\x75\x74\x6F\x53\x65\x63'

# Publish periodically
for i in {1..5}; do
    mosquitto_pub -h localhost -t "test/count" -m "Counter: $i"
    sleep 1
done

Basic Subscribing (mosquitto_sub)

Basic subscription commands:

# Subscribe to a single topic
mosquitto_sub -h localhost -t "test/topic"

# Subscribe with QoS 1
mosquitto_sub -h localhost -t "test/topic" -q 1

# Subscribe to multiple topics
mosquitto_sub -h localhost -t "test/topic1" -t "test/topic2"

# Subscribe using wildcards
mosquitto_sub -h localhost -t "test/#"    # Multi-level wildcard
mosquitto_sub -h localhost -t "test/+" -v # Single-level wildcard

# Subscribe and log to file
mosquitto_sub -h localhost -t "test/#" -v | tee mqtt_log.txt

Authentication and Security

When working with secured MQTT brokers, you'll need these authentication commands as below:

# Username and password authentication
mosquitto_pub -h localhost -t "test/topic" -m "secure message" -u "username" -P "password"
mosquitto_sub -h localhost -t "test/topic" -u "username" -P "password"

# TLS/SSL encryption without certificate verification
mosquitto_pub -h localhost -t "test/topic" -m "encrypted" --insecure -p 8883
mosquitto_sub -h localhost -t "test/topic" --insecure -p 8883

# TLS/SSL with certificate verification
mosquitto_pub -h localhost -t "test/topic" -m "verified" --cafile /path/to/ca.crt --cert /path/to/client.crt --key /path/to/client.key
mosquitto_sub -h localhost -t "test/topic" --cafile /path/to/ca.crt --cert /path/to/client.crt --key /path/to/client.key

Debugging and Troubleshooting

Commands useful for debugging MQTT communications:

# Debug mode (show extra information)
mosquitto_sub -h localhost -t "test/#" -d

# Show verbose output
mosquitto_sub -h localhost -t "test/#" -v -d

# Print only messages (no other output)
mosquitto_sub -h localhost -t "test/#" --quiet

# Show connection details
mosquitto_sub -h localhost -t "test/#" -d -v --quiet

Common Options Reference

Here are the most commonly used options for both clients:

General Options

• -h : Broker host

• -p : Broker port (default: 1883)

• -u : Username

• -P : Password

• -i : Client ID (useful for eliminating the existing node by spoofing)

• -d : Enable debug messages

• --quiet : Suppress non-essential output

• -v : Be more verbose

• -V : Specify the MQTT protocol's version to use ( e.g.; mqttv31, mqttv311. defaults is mqttv31)

Publishing Options

• -t : Topic to publish to

• -m : Message payload

• -f : File to read message from

• -l : Read messages from stdin line by line

• -n : Send null message

• -r : Make message retained

• -q : Quality of Service (0, 1, or 2)

Subscription Options

• -t : Topic to subscribe to (can be used multiple times)

• -R : Do not print stale messages (those with retain set)

• -c : Disable clean session

• -N : Do not add newlines after messages

• -v : Print topic name with message

Sample Bash Script for Controlling Vehicle

A sample bash script for controlling a vehicle via MQTT using mosquitto-clients.

#!/bin/bash
# vehicle_control.sh
BROKER="localhost"
VEHICLE="VEHXX1"

case $1 in
    "lock")
        mosquitto_pub -h $BROKER \
            -t "vehicle/$VEHICLE/command/doors" \
            -m '{"action": "lock", "door": "all"}'
        ;;
    "unlock")
        mosquitto_pub -h $BROKER \
            -t "vehicle/$VEHICLE/command/doors" \
            -m '{"action": "unlock", "door": "all"}'
        ;;
    "ac_on")
        mosquitto_pub -h $BROKER \
            -t "vehicle/$VEHICLE/command/climate" \
            -m '{"action": "on", "temperature": 20}'
        ;;
    "ac_off")
        mosquitto_pub -h $BROKER \
            -t "vehicle/$VEHICLE/command/climate" \
            -m '{"action": "off"}'
        ;;
    *)
        echo "Usage: $0 [lock|unlock|ac_on|ac_off]"
        ;;
esac

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How to Perform Security Testing of MQTT?

Find out the answer below.

• MQTT Security 101

• MQTT in Connected Cars and Hacking Them