readme.txt

SSL/TLS connection from Eclipse Paho Java client to mosquitto MQTT broker

By Sharon Ben Asher
AVG Mobilation
[email protected]

Mosquitto is an Open Source MQTT v3.1 Broker written in C (http://mosquitto.org)
Eclipse Paho project has a Java MQTT client (http://eclipse.org/paho/)

The code snippet below demonstrates how to establish a secured connection from a Paho client to a mosquitto broker.
The connection includes server and client authentication through openssl (PEM formatted) certificates.

1) Follow the instructions on the mosquitto site to produce all the necessary certificates 
   http://mosquitto.org/man/mosquitto-tls-7.html

2) Configure the broker to expect SSL connections.
example configuration:
listener 1883
cafile /home/ubuntu/etc/ca.crt
certfile /home/ubuntu/etc/server.crt
keyfile /home/ubuntu/etc/server.key
require_certificate true
use_identity_as_username true

3) On the client side, Paho has several options for specifying properties for the creation of SSL sockets 
   (Properties, JVM arguments, etc).  However, none of them will work with mosquitto (historically, Paho worked with IBM brokers). 
   Fortunately, it also accepts a custom made instance of javax.net.ssl.SSLSocketFactory through the method MqttConnectOptions.setSocketFactory() and this works.

example code using Paho API to establish connection:

	String serverUrl = "ssl://myMosquittoServer.com:1883";
	MqttClient client = new MqttClient(serverUrl, "consumerId" , null);
	client.setCallback(new MyCallback());
	MqttConnectOptions options = new MqttConnectOptions();
	options.setConnectionTimeout(60);
	options.setKeepAliveInterval(60);
	options.setSocketFactory(SslUtil.getSocketFactory("caFilePath", "clientCrtFilePath", "clientKeyFilePath", "password"));
	client.connect(options);
	client.subscribe("topic", 0);

The interesting bit is, of course, SslUtil.getSocketFactory() method.  The code is attached seperately.
Since Java cannot read PEM formatted certificates, the method is using bouncy castle (http://www.bouncycastle.org/) to load the necessary files:
ca.crt is used to authenticate the server and is used to init an instance of javax.net.ssl.TrustManagerFactory. 
client.crt/.key are sent to mosquitto for client authentication, and therefore are used to init an instance of javax.net.ssl.KeyManagerFactory.
The method expects all files as String full paths.
The method is using Files.readAllBytes() which is available in JDK 7. 
basically, you need to load the file into byte array and pass that array to the constructor of ByteArrayInputStream as is demonstrated in the code.

SslUtil.java

import java.io.*;
import java.nio.file.*;
import java.security.*;
import java.security.cert.*;
import javax.net.ssl.*;

import org.bouncycastle.jce.provider.*;
import org.bouncycastle.openssl.*;

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

		// load CA certificate
		PEMReader reader = new PEMReader(new InputStreamReader(new ByteArrayInputStream(Files.readAllBytes(Paths.get(caCrtFile)))));
		X509Certificate caCert = (X509Certificate)reader.readObject();
		reader.close();

		// load client certificate
		reader = new PEMReader(new InputStreamReader(new ByteArrayInputStream(Files.readAllBytes(Paths.get(crtFile)))));
		X509Certificate cert = (X509Certificate)reader.readObject();
		reader.close();

		// load client private key
		reader = new PEMReader(
				new InputStreamReader(new ByteArrayInputStream(Files.readAllBytes(Paths.get(keyFile)))),
				new PasswordFinder() {
					@Override
					public char[] getPassword() {
						return password.toCharArray();
					}
				}
		);
		KeyPair key = (KeyPair)reader.readObject();
		reader.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(TrustManagerFactory.getDefaultAlgorithm());
		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");
		context.init(kmf.getKeyManagers(), tmf.getTrustManagers(), null);

		return context.getSocketFactory();
	}
}