accepting HTTPS connections with self-signed certificates

The following main steps are required to achieve a secured connection from Certification Authorities which are not considered as trusted by the android platform.

As requested by many users, I've mirrored the most important parts from my blog article here:

  1. Grab all required certificates (root and any intermediate CA’s)
  2. Create a keystore with keytool and the BouncyCastle provider and import the certs
  3. Load the keystore in your android app and use it for the secured connections (I recommend to use the Apache HttpClient instead of the standard java.net.ssl.HttpsURLConnection (easier to understand, more performant)

Grab the certs

You have to obtain all certificates that build a chain from the endpoint certificate the whole way up to the Root CA. This means, any (if present) Intermediate CA certs and also the Root CA cert. You don’t need to obtain the endpoint certificate.

Create the keystore

Download the BouncyCastle Provider and store it to a known location. Also ensure that you can invoke the keytool command (usually located under the bin folder of your JRE installation).

Now import the obtained certs (don’t import the endpoint cert) into a BouncyCastle formatted keystore.

I didn’t test it, but I think the order of importing the certificates is important. This means, import the lowermost Intermediate CA certificate first and then all the way up to the Root CA certificate.

With the following command a new keystore (if not already present) with the password mysecret will be created and the Intermediate CA certificate will be imported. I also defined the BouncyCastle provider, where it can be found on my file system and the keystore format. Execute this command for each certificate in the chain.

keytool -importcert -v -trustcacerts -file "path_to_cert/interm_ca.cer" -alias IntermediateCA -keystore "res/raw/mykeystore.bks" -provider org.bouncycastle.jce.provider.BouncyCastleProvider -providerpath "path_to_bouncycastle/bcprov-jdk16-145.jar" -storetype BKS -storepass mysecret

Verify if the certificates were imported correctly into the keystore:

keytool -list -keystore "res/raw/mykeystore.bks" -provider org.bouncycastle.jce.provider.BouncyCastleProvider -providerpath "path_to_bouncycastle/bcprov-jdk16-145.jar" -storetype BKS -storepass mysecret

Should output the whole chain:

RootCA, 22.10.2010, trustedCertEntry, Thumbprint (MD5): 24:77:D9:A8:91:D1:3B:FA:88:2D:C2:FF:F8:CD:33:93
IntermediateCA, 22.10.2010, trustedCertEntry, Thumbprint (MD5): 98:0F:C3:F8:39:F7:D8:05:07:02:0D:E3:14:5B:29:43

Now you can copy the keystore as a raw resource in your android app under res/raw/

Use the keystore in your app

First of all we have to create a custom Apache HttpClient that uses our keystore for HTTPS connections:

import org.apache.http.*

public class MyHttpClient extends DefaultHttpClient {

    final Context context;

    public MyHttpClient(Context context) {
        this.context = context;
    }

    @Override
    protected ClientConnectionManager createClientConnectionManager() {
        SchemeRegistry registry = new SchemeRegistry();
        registry.register(new Scheme("http", PlainSocketFactory.getSocketFactory(), 80));
        // Register for port 443 our SSLSocketFactory with our keystore
        // to the ConnectionManager
        registry.register(new Scheme("https", newSslSocketFactory(), 443));
        return new SingleClientConnManager(getParams(), registry);
    }

    private SSLSocketFactory newSslSocketFactory() {
        try {
            // Get an instance of the Bouncy Castle KeyStore format
            KeyStore trusted = KeyStore.getInstance("BKS");
            // Get the raw resource, which contains the keystore with
            // your trusted certificates (root and any intermediate certs)
            InputStream in = context.getResources().openRawResource(R.raw.mykeystore);
            try {
                // Initialize the keystore with the provided trusted certificates
                // Also provide the password of the keystore
                trusted.load(in, "mysecret".toCharArray());
            } finally {
                in.close();
            }
            // Pass the keystore to the SSLSocketFactory. The factory is responsible
            // for the verification of the server certificate.
            SSLSocketFactory sf = new SSLSocketFactory(trusted);
            // Hostname verification from certificate
            // http://hc.apache.org/httpcomponents-client-ga/tutorial/html/connmgmt.html#d4e506
            sf.setHostnameVerifier(SSLSocketFactory.STRICT_HOSTNAME_VERIFIER);
            return sf;
        } catch (Exception e) {
            throw new AssertionError(e);
        }
    }
}

We have created our custom HttpClient, now we can use it for secure connections. For example when we make a GET call to a REST resource:

// Instantiate the custom HttpClient
DefaultHttpClient client = new MyHttpClient(getApplicationContext());
HttpGet get = new HttpGet("https://www.mydomain.ch/rest/contacts/23");
// Execute the GET call and obtain the response
HttpResponse getResponse = client.execute(get);
HttpEntity responseEntity = getResponse.getEntity();

That's it ;)


If you have a custom/self-signed certificate on server that is not there on device, you can use the below class to load it and use it on client side in Android:

Place the certificate *.crt file in /res/raw so that it is available from R.raw.*

Use below class to obtain an HTTPClient or HttpsURLConnection which will have a socket factory using that certificate :

package com.example.customssl;

import android.content.Context;
import org.apache.http.client.HttpClient;
import org.apache.http.conn.scheme.PlainSocketFactory;
import org.apache.http.conn.scheme.Scheme;
import org.apache.http.conn.scheme.SchemeRegistry;
import org.apache.http.conn.ssl.AllowAllHostnameVerifier;
import org.apache.http.conn.ssl.SSLSocketFactory;
import org.apache.http.impl.client.DefaultHttpClient;
import org.apache.http.impl.conn.tsccm.ThreadSafeClientConnManager;
import org.apache.http.params.BasicHttpParams;
import org.apache.http.params.HttpParams;

import javax.net.ssl.HttpsURLConnection;
import javax.net.ssl.SSLContext;
import javax.net.ssl.TrustManagerFactory;
import java.io.IOException;
import java.io.InputStream;
import java.net.URL;
import java.security.KeyStore;
import java.security.KeyStoreException;
import java.security.NoSuchAlgorithmException;
import java.security.cert.Certificate;
import java.security.cert.CertificateException;
import java.security.cert.CertificateFactory;

public class CustomCAHttpsProvider {

    /**
     * Creates a {@link org.apache.http.client.HttpClient} which is configured to work with a custom authority
     * certificate.
     *
     * @param context       Application Context
     * @param certRawResId  R.raw.id of certificate file (*.crt). Should be stored in /res/raw.
     * @param allowAllHosts If true then client will not check server against host names of certificate.
     * @return Http Client.
     * @throws Exception If there is an error initializing the client.
     */
    public static HttpClient getHttpClient(Context context, int certRawResId, boolean allowAllHosts) throws Exception {


        // build key store with ca certificate
        KeyStore keyStore = buildKeyStore(context, certRawResId);

        // init ssl socket factory with key store
        SSLSocketFactory sslSocketFactory = new SSLSocketFactory(keyStore);

        // skip hostname security check if specified
        if (allowAllHosts) {
            sslSocketFactory.setHostnameVerifier(new AllowAllHostnameVerifier());
        }

        // basic http params for client
        HttpParams params = new BasicHttpParams();

        // normal scheme registry with our ssl socket factory for "https"
        SchemeRegistry schemeRegistry = new SchemeRegistry();
        schemeRegistry.register(new Scheme("http", PlainSocketFactory.getSocketFactory(), 80));
        schemeRegistry.register(new Scheme("https", sslSocketFactory, 443));

        // create connection manager
        ThreadSafeClientConnManager cm = new ThreadSafeClientConnManager(params, schemeRegistry);

        // create http client
        return new DefaultHttpClient(cm, params);
    }

    /**
     * Creates a {@link javax.net.ssl.HttpsURLConnection} which is configured to work with a custom authority
     * certificate.
     *
     * @param urlString     remote url string.
     * @param context       Application Context
     * @param certRawResId  R.raw.id of certificate file (*.crt). Should be stored in /res/raw.
     * @param allowAllHosts If true then client will not check server against host names of certificate.
     * @return Http url connection.
     * @throws Exception If there is an error initializing the connection.
     */
    public static HttpsURLConnection getHttpsUrlConnection(String urlString, Context context, int certRawResId,
                                                           boolean allowAllHosts) throws Exception {

        // build key store with ca certificate
        KeyStore keyStore = buildKeyStore(context, certRawResId);

        // Create a TrustManager that trusts the CAs in our KeyStore
        String tmfAlgorithm = TrustManagerFactory.getDefaultAlgorithm();
        TrustManagerFactory tmf = TrustManagerFactory.getInstance(tmfAlgorithm);
        tmf.init(keyStore);

        // Create an SSLContext that uses our TrustManager
        SSLContext sslContext = SSLContext.getInstance("TLS");
        sslContext.init(null, tmf.getTrustManagers(), null);

        // Create a connection from url
        URL url = new URL(urlString);
        HttpsURLConnection urlConnection = (HttpsURLConnection) url.openConnection();
        urlConnection.setSSLSocketFactory(sslContext.getSocketFactory());

        // skip hostname security check if specified
        if (allowAllHosts) {
            urlConnection.setHostnameVerifier(new AllowAllHostnameVerifier());
        }

        return urlConnection;
    }

    private static KeyStore buildKeyStore(Context context, int certRawResId) throws KeyStoreException, CertificateException, NoSuchAlgorithmException, IOException {
        // init a default key store
        String keyStoreType = KeyStore.getDefaultType();
        KeyStore keyStore = KeyStore.getInstance(keyStoreType);
        keyStore.load(null, null);

        // read and add certificate authority
        Certificate cert = readCert(context, certRawResId);
        keyStore.setCertificateEntry("ca", cert);

        return keyStore;
    }

    private static Certificate readCert(Context context, int certResourceId) throws CertificateException, IOException {

        // read certificate resource
        InputStream caInput = context.getResources().openRawResource(certResourceId);

        Certificate ca;
        try {
            // generate a certificate
            CertificateFactory cf = CertificateFactory.getInstance("X.509");
            ca = cf.generateCertificate(caInput);
        } finally {
            caInput.close();
        }

        return ca;
    }

}

Key points:

  1. Certificate objects are generated from .crt files.
  2. A default KeyStore is created.
  3. keyStore.setCertificateEntry("ca", cert) is adding certificate to key store under alias "ca". You modify the code to add more certificates (intermediate CA etc).
  4. Main objective is to generate a SSLSocketFactory which can then be used by HTTPClient or HttpsURLConnection.
  5. SSLSocketFactory can be configured further, for example to skip host name verification etc.

More information at : http://developer.android.com/training/articles/security-ssl.html


The first thing you need to do is to set the level of verification. Such levels is not so much:

  • ALLOW_ALL_HOSTNAME_VERIFIER
  • BROWSER_COMPATIBLE_HOSTNAME_VERIFIER
  • STRICT_HOSTNAME_VERIFIER

Although the method setHostnameVerifier() is obsolete for new library apache, but for version in Android SDK is normal. And so we take ALLOW_ALL_HOSTNAME_VERIFIER and set it in the method factory SSLSocketFactory.setHostnameVerifier().

Next, You need set our factory for the protocol to https. To do this, simply call the SchemeRegistry.register() method.

Then you need to create a DefaultHttpClient with SingleClientConnManager. Also in the code below you can see that on default will also use our flag (ALLOW_ALL_HOSTNAME_VERIFIER) by the method HttpsURLConnection.setDefaultHostnameVerifier()

Below code works for me:

HostnameVerifier hostnameVerifier = org.apache.http.conn.ssl.SSLSocketFactory.ALLOW_ALL_HOSTNAME_VERIFIER;

DefaultHttpClient client = new DefaultHttpClient();

SchemeRegistry registry = new SchemeRegistry();
SSLSocketFactory socketFactory = SSLSocketFactory.getSocketFactory();
socketFactory.setHostnameVerifier((X509HostnameVerifier) hostnameVerifier);
registry.register(new Scheme("https", socketFactory, 443));
SingleClientConnManager mgr = new SingleClientConnManager(client.getParams(), registry);
DefaultHttpClient httpClient = new DefaultHttpClient(mgr, client.getParams());

// Set verifier     
HttpsURLConnection.setDefaultHostnameVerifier(hostnameVerifier);

// Example send http request
final String url = "https://encrypted.google.com/";
HttpPost httpPost = new HttpPost(url);
HttpResponse response = httpClient.execute(httpPost);

Tags:

Ssl

Https

Android

Ca

Httpclient

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