Secure Wi-Fi Connection with TLS on ESP8266

Difficulty Level: Intermediate

In this tutorial, we will configure the ESP8266 to establish a secure Wi-Fi connection using TLS (Transport Layer Security). TLS helps secure data transmitted over the network by encrypting it and verifying the identity of the server, which is essential for IoT applications dealing with sensitive data.

Components Required

• ESP8266 Module (e.g., NodeMCU or ESP-01)
• Wi-Fi access point
• Arduino IDE

Step 1: Install Necessary Libraries

To begin, make sure the **ESP8266WiFi** and **BearSSL** libraries are installed. These libraries provide the tools for creating a secure TLS connection. The ESP8266 core for Arduino comes preloaded with these libraries:

• **ESP8266WiFi** for Wi-Fi connectivity
• **BearSSL** for secure communications via TLS

Step 2: Connect to Wi-Fi

First, connect the ESP8266 to a Wi-Fi network. You need the SSID and password of the Wi-Fi network to establish a basic connection:

#include 

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

void setup() {
  Serial.begin(115200);
  WiFi.begin(ssid, password);

  while (WiFi.status() != WL_CONNECTED) {
    delay(1000);
    Serial.println("Connecting to WiFi...");
  }
  Serial.println("Connected to WiFi!");
}
        

Step 3: Set Up a Secure TLS Connection

To securely communicate with a server using TLS, use **WiFiClientSecure**. This client supports SSL/TLS connections. You can also specify the server’s certificate to ensure authenticity.

#include 

const char* host = "your_server.com";  // Replace with your server
const int port = 443;  // Default HTTPS port

// Server certificate fingerprint (SHA-1)
const char* fingerprint = "XX XX XX XX XX XX XX XX XX XX XX XX XX XX XX XX XX XX XX XX"; 

WiFiClientSecure client;

void setup() {
  Serial.begin(115200);
  WiFi.begin(ssid, password);

  while (WiFi.status() != WL_CONNECTED) {
    delay(1000);
    Serial.println("Connecting to WiFi...");
  }
  Serial.println("Connected to WiFi!");

  client.setFingerprint(fingerprint);  // Set the server certificate fingerprint

  if (!client.connect(host, port)) {
    Serial.println("Connection failed!");
    return;
  }

  Serial.println("Connected to server!");
  
  // Sending a simple GET request
  client.println("GET /path HTTP/1.1");
  client.println("Host: your_server.com");
  client.println("Connection: close");
  client.println();
  
  // Reading the response
  while (client.connected()) {
    String line = client.readStringUntil('\n');
    if (line == "\r") {
      break;
    }
    Serial.println(line);
  }
}

void loop() {
  // Nothing here
}
        

Step 4: Obtaining the Certificate Fingerprint

To securely connect using a certificate, you need to obtain the server’s SSL certificate fingerprint. You can do this using a tool like **OpenSSL**:

• In the terminal, run:

  openssl s_client -connect your_server.com:443

• Once the certificate details are displayed, copy the **SHA1** fingerprint and use it in the **setFingerprint()** method as shown in the code above.

Step 5: Error Handling

Ensure proper error handling is in place for secure connections:

• If the server’s certificate fingerprint does not match the expected value, the connection should fail.
• Handle timeouts and disconnections gracefully to avoid abrupt failures.

Conclusion

By following these steps, you can create a secure Wi-Fi connection using TLS on your ESP8266. This is critical for securing communication between IoT devices and servers, especially when handling sensitive information like sensor data or controlling devices remotely.