Secure IoT Data Transmission: Implement MQTT over TLS with ESP32 and MbedTLS

Introduction

In this tutorial, we will cover how to implement MQTT over TLS using the ESP32 microcontroller and the MbedTLS library. This setup ensures secure data transmission for your IoT projects. By the end, you will be able to connect your ESP32 to an MQTT broker securely using TLS encryption.

Prerequisites

• Basic knowledge of C/C++ programming
• ESP32 development board
• Arduino IDE or PlatformIO installed
• MQTT broker (e.g., Mosquitto) configured for TLS
• OpenSSL or equivalent to generate certificates

Parts/Tools

• ESP32 Development Board
• USB cable for programming
• Computer with the Arduino IDE or PlatformIO
• OpenSSL for certificate generation

Steps

1. Generate TLS Certificates
   1. Install OpenSSL if not already installed.
   2. Generate a private key:

   openssl genrsa -out ca.key 2048

   3. Create a Certificate Signing Request (CSR):

   openssl req -new -key ca.key -out ca.csr

   4. Generate the self-signed certificate:

   openssl x509 -req -in ca.csr -signkey ca.key -out ca.crt -days 365

   5. Convert the certificate to DER format for compatibility:

   openssl x509 -in ca.crt -outform der -out ca.der

2. Set Up the Arduino IDE
   1. Open the Arduino IDE.
   2. Install the necessary libraries:
      • MQTT Client library (e.g., PubSubClient)
      • MbedTLS library (included in ESP32 core)
   3. Ensure you have the ESP32 board package installed.
3. Write the Code
   1. Open a new sketch in the Arduino IDE.
   2. Include necessary libraries:

   #include 
   #include 
   #include 
   

   3. Define your Wi-Fi and MQTT broker credentials:

   const char* ssid = "your_SSID";
   const char* password = "your_PASSWORD";
   const char* mqtt_server = "your_broker_address";
   

   4. Set up Wi-Fi connection:

   void setup_wifi() {
       delay(10);
       WiFi.begin(ssid, password);
       while (WiFi.status() != WL_CONNECTED) {
           delay(500);
       }
   }

   5. Configure the MQTT client:

   WiFiClientSecure espClient;
   PubSubClient client(espClient);
   

   6. Load the certificate:

   espClient.setCACert(ca_crt); // Load the CA certificate
   

   7. Connect to the MQTT broker:

   void reconnect() {
       while (!client.connected()) {
           if (client.connect("ESP32Client")) {
               // Successfully connected
           } else {
               delay(5000);
           }
       }
   }

   8. Publish data securely:

   client.publish("topic/test", "Hello MQTT over TLS");
   

4. Upload and Test the Code
   1. Connect your ESP32 to your computer.
   2. Select the correct board and port in the Arduino IDE.
   3. Upload the code.
   4. Open the Serial Monitor to check for connection status and published messages.

Troubleshooting

• Connection Issues: Ensure your Wi-Fi credentials and MQTT broker address are correct.
• Certificate Errors: Verify that the CA certificate is correctly loaded and in the right format.
• MQTT Connection Refused: Check if the MQTT broker is configured to accept TLS connections.
• ESP32 not connecting to Wi-Fi: Confirm the Wi-Fi network is operational and within range.

Conclusion

By following this tutorial, you have successfully implemented MQTT over TLS using the ESP32 and MbedTLS library. This setup enhances the security of your IoT applications by encrypting the data transmitted between the device and the MQTT broker. For further exploration, consider experimenting with different MQTT functionalities and scaling your secure IoT solutions.