Question

We are researching a push notifications platform for Android (a failover for Google’s C2DM)
I am using the Eclipse Paho Java client to connect to mosquitto broker (1.0.3). The broker is installed on a Ubuntu 12.04 (AWS EC2 instance)
I successfully connected the client to the server using non encrypted TCP connection.
By the way, after tweaking kernel params, I was able to open 100K concurrent clients to one broker instance on a medium sized EC2 machine. Good work, mosquitto!

Now I am trying to set up a secured connection using SSL. I want to authenticate the client using a client certificate.
I followed the explanations in mosquito_tls page and generated the keys and self-signed certificates for server and client.
Configured the server to use SSL.

For the client part, I looked at the signature of mosquitto_tls_set and took note that it requires the CA certificate, client key and certificate files.
I figured that the CA certificate is used for the client to authenticate the server, while the client key and certificate are used for the server to authenticate the client.
Am I right?

So I here is what I did on the Java side:

1. Use bouncy castle to load the three abovementioned files.
2. Put the CA certificate in a keystore and used it to create a TrustManagerFactory.
3. Put the client key and certificate in another keystore and used it to create a
   KeyManagerFactory.
4. Created an SSLContext an initialized it with the two factories.
5. Created an SSLSocketFactory from the SSLContext and passed it to the Paho’s MqttConnectOptions

When I do the connect, I get the following error from mosquitto

OpenSSL Error: error:140890B2:SSL routines:SSL3_GET_CLIENT_CERTIFICATE:no certificate returned
Socket read error on client (null), disconnecting.

Edit:
now I see on the client side the following exception

javax.net.ssl.SSLHandshakeException: Received fatal alert: unknown_ca

Here’s the full code

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

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

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

    reader = new PEMReader(
            new InputStreamReader(new ByteArrayInputStream(Files.readAllBytes(Paths.get(keyFile)))),
            new PasswordFinder() {
                public char[] getPassword() {
                    return password.toCharArray();
                }
            }
    );
    KeyPair key = (KeyPair)reader.readObject();
    reader.close();

    KeyStore caKs = KeyStore.getInstance("JKS");
    caKs.load(null, null);
    caKs.setCertificateEntry("ca-certificate", caCert);
    TrustManagerFactory tmf = TrustManagerFactory.getInstance("PKIX");
    tmf.init(caKs);

    KeyStore ks = KeyStore.getInstance("JKS");
    ks.load(null, null);
    ks.setCertificateEntry("certificate", cert);
    ks.setKeyEntry("private-key", key.getPrivate(), password.toCharArray(), new java.security.cert.Certificate[]{cert});
    //ks.setKeyEntry("public-key", key.getPublic(), password.toCharArray(), new java.security.cert.Certificate[]{cert});
    KeyManagerFactory kmf = KeyManagerFactory.getInstance("SunX509");
    kmf.init(ks, password.toCharArray());

    SSLContext context = SSLContext.getInstance("SSLv3");
    context.init(kmf.getKeyManagers(), tmf.getTrustManagers(), null);

    return context.getSocketFactory();
}

The mosquito.conf looks like this

# general options
pid_file /home/ubuntu/mosquitto.pid

# persistence
queue_qos0_messages false
persistence false

# logging
log_dest stdout
connection_messages true
log_timestamp false

# default listener
# disable default listener (open only SSL listener)
#port 1883
#max_connections -1

# SSL listener
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
max_connections -1

Answer 1

ok, after some support from mosquitto developer (thx, Roger Light) we figured out the problem.
the details you provide when generating certificate (company, organization unit, common name) must be different in the CA, client and server certificates.
otherwise the code works with some minor changes. I repost here the correct code with some comments for clarity:

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

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

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() {
                public char[] getPassword() {
                    return password.toCharArray();
                }
            }
    );
    KeyPair key = (KeyPair)reader.readObject();
    reader.close();

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

    // client key and certificates are sent to server so it can authenticate us
    KeyStore ks = KeyStore.getInstance("JKS");
    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("PKIX");
    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();
}