A simple java code for SSL/TLS connection from Paho java client to mosquitto MQTT broker

TestMQTT.java

package test_mqtt;

import java.io.BufferedInputStream;
import java.io.FileInputStream;
import java.io.FileReader;
import java.security.KeyPair;
import java.security.KeyStore;
import java.security.Security;
import java.security.cert.CertificateFactory;
import java.security.cert.X509Certificate;

import javax.net.ssl.KeyManagerFactory;
import javax.net.ssl.SSLContext;
import javax.net.ssl.SSLSocketFactory;
import javax.net.ssl.TrustManagerFactory;

import org.bouncycastle.jce.provider.BouncyCastleProvider;
import org.bouncycastle.openssl.PEMDecryptorProvider;
import org.bouncycastle.openssl.PEMEncryptedKeyPair;
import org.bouncycastle.openssl.PEMKeyPair;
import org.bouncycastle.openssl.PEMParser;
import org.bouncycastle.openssl.jcajce.JcaPEMKeyConverter;
import org.bouncycastle.openssl.jcajce.JcePEMDecryptorProviderBuilder;
import org.eclipse.paho.client.mqttv3.MqttClient;
import org.eclipse.paho.client.mqttv3.MqttConnectOptions;
import org.eclipse.paho.client.mqttv3.MqttException;

public class TestMQTT {

	public static void main(String[] args) {
		
		String serverUrl = "ssl://serverip:1883";
		String caFilePath = "/your_ssl/cacert.pem";
		String clientCrtFilePath = "/your_ssl/client.pem";
		String clientKeyFilePath = "/your_ssl/client.key";
		String mqttUserName = "guest";
		String mqttPassword = "123123";
		
		MqttClient client;
		try {
			client = new MqttClient(serverUrl, "2");
			MqttConnectOptions options = new MqttConnectOptions();
			options.setUserName(mqttUserName);
			options.setPassword(mqttPassword.toCharArray());
			
			options.setConnectionTimeout(60);
			options.setKeepAliveInterval(60);
			options.setMqttVersion(MqttConnectOptions.MQTT_VERSION_3_1);

			
			SSLSocketFactory socketFactory = getSocketFactory(caFilePath,
					clientCrtFilePath, clientKeyFilePath, "");
			options.setSocketFactory(socketFactory);

			System.out.println("starting connect the server...");
			client.connect(options);
			System.out.println("connected!");
			Thread.sleep(1000);

			client.subscribe(
					"/u/56ca327d17531d08e76bddd4a215e37f5fd6082f7442151c4d3f1d100a0ffd4e",
					0);
			client.disconnect();
			System.out.println("disconnected!");


		} catch (MqttException e) {
			e.printStackTrace();
		} catch (Exception e) {
			e.printStackTrace();
		}

	}

	private static SSLSocketFactory getSocketFactory(final String caCrtFile,
			final String crtFile, final String keyFile, final String password)
			throws Exception {
		Security.addProvider(new BouncyCastleProvider());

		// load CA certificate
		X509Certificate caCert = null;

		FileInputStream fis = new FileInputStream(caCrtFile);
		BufferedInputStream bis = new BufferedInputStream(fis);
		CertificateFactory cf = CertificateFactory.getInstance("X.509");

		while (bis.available() > 0) {
			caCert = (X509Certificate) cf.generateCertificate(bis);
			// System.out.println(caCert.toString());
		}

		// load client certificate
		bis = new BufferedInputStream(new FileInputStream(crtFile));
		X509Certificate cert = null;
		while (bis.available() > 0) {
			cert = (X509Certificate) cf.generateCertificate(bis);
			// System.out.println(caCert.toString());
		}

		// load client private key
		PEMParser pemParser = new PEMParser(new FileReader(keyFile));
		Object object = pemParser.readObject();
		PEMDecryptorProvider decProv = new JcePEMDecryptorProviderBuilder()
				.build(password.toCharArray());
		JcaPEMKeyConverter converter = new JcaPEMKeyConverter()
				.setProvider("BC");
		KeyPair key;
		if (object instanceof PEMEncryptedKeyPair) {
			System.out.println("Encrypted key - we will use provided password");
			key = converter.getKeyPair(((PEMEncryptedKeyPair) object)
					.decryptKeyPair(decProv));
		} else {
			System.out.println("Unencrypted key - no password needed");
			key = converter.getKeyPair((PEMKeyPair) object);
		}
		pemParser.close();

		// CA certificate is used to authenticate server
		KeyStore caKs = KeyStore.getInstance(KeyStore.getDefaultType());
		caKs.load(null, null);
		caKs.setCertificateEntry("ca-certificate", caCert);
		TrustManagerFactory tmf = TrustManagerFactory.getInstance("X509");
		tmf.init(caKs);

		// client key and certificates are sent to server so it can authenticate
		// us
		KeyStore ks = KeyStore.getInstance(KeyStore.getDefaultType());
		ks.load(null, null);
		ks.setCertificateEntry("certificate", cert);
		ks.setKeyEntry("private-key", key.getPrivate(), password.toCharArray(),
				new java.security.cert.Certificate[] { cert });
		KeyManagerFactory kmf = KeyManagerFactory.getInstance(KeyManagerFactory
				.getDefaultAlgorithm());
		kmf.init(ks, password.toCharArray());

		// finally, create SSL socket factory
		SSLContext context = SSLContext.getInstance("TLSv1.2");
		context.init(kmf.getKeyManagers(), tmf.getTrustManagers(), null);

		return context.getSocketFactory();
	}

}

Dear all,
If I have only cert.pem, privkey.pem. How can I connect to MQTT Broker.
I can conenct to MQTT Broker by using Python and React, but can not conenct to MQTT Broker by using Java/Kotlin.
Please help me. Thanks a lots

In my case I have only client certificate (crt) and client key (key) files, how can I connect to Azure Event Grid MQTT. With the above code I get error as follows:
javax.net.ssl.SSLException: Unexpected error: java.security.InvalidAlgorithmParameterException: the trustAnchors parameter must be non-empty

I checked in other MQTT client like MQTTBox and MQTTX the connection is successful by using only client certificate and client key.

@mluis , et. al. - Does this connect to AWS IOT core using X.509 cert authentication to port 8883?

I have only a slight difference in sample project below because it seems that bouncycastle is being deprecated, but since private key and cert is properly parsed into a data structure and successful connection to mosquitto.org:8883 proves it works.

https://github.com/srlohr/PublicPahoClient.git

eclipse/paho.mqtt.java#972

https://stackoverflow.com/questions/74725722/paho-mqtt-android-client-to-aws-iot-connection-failure-connection-lost-32109

yes it worked at the time for aws iot

Hi All

I am getting the following error show below when running with JDK 12. Any idea, thank you for your help.

20:52:36.312 [main] INFO au.gov.nsw.rms.its.sdcs.mb.vernemq.TestMQTTSSL - starting connect the server... 20:52:36.454 [main] ERROR au.gov.nsw.rms.its.sdcs.mb.vernemq.TestMQTTSSL - Exception encounter with error MqttException org.eclipse.paho.client.mqttv3.MqttException: MqttException at org.eclipse.paho.client.mqttv3.internal.ExceptionHelper.createMqttException(ExceptionHelper.java:38) at org.eclipse.paho.client.mqttv3.internal.ClientComms$ConnectBG.run(ClientComms.java:738) at java.base/java.lang.Thread.run(Thread.java:835) Caused by: javax.net.ssl.SSLHandshakeException: No subject alternative names present at java.base/sun.security.ssl.Alert.createSSLException(Alert.java:131) at java.base/sun.security.ssl.TransportContext.fatal(TransportContext.java:320) at java.base/sun.security.ssl.TransportContext.fatal(TransportContext.java:263) at java.base/sun.security.ssl.TransportContext.fatal(TransportContext.java:258) at java.base/sun.security.ssl.CertificateMessage$T12CertificateConsumer.checkServerCerts(CertificateMessage.java:641) at java.base/sun.security.ssl.CertificateMessage$T12CertificateConsumer.onCertificate(CertificateMessage.java:460) at java.base/sun.security.ssl.CertificateMessage$T12CertificateConsumer.consume(CertificateMessage.java:360) at java.base/sun.security.ssl.SSLHandshake.consume(SSLHandshake.java:392) at java.base/sun.security.ssl.HandshakeContext.dispatch(HandshakeContext.java:443) at java.base/sun.security.ssl.HandshakeContext.dispatch(HandshakeContext.java:421) at java.base/sun.security.ssl.TransportContext.dispatch(TransportContext.java:177)

  //禁止服务端检查
  options.setHttpsHostnameVerificationEnabled(false);

Works like a charm for AWS IoT. I'm using OpenJDK 21, with paho mqtt v5. Only some small modifications to adapt to v5 API is needed.