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accepting HTTPS connections with self-signed certificates


Question

I'm trying to make HTTPS connections, using HttpClient lib, but the problem is that, since the certificate isn't signed by a recognized Certificate Authority (CA) like Verisign,GlobalSIgn, etc., listed on the set of Android Trusted Certificates, I keep getting javax.net.ssl.SSLException: Not trusted server certificate.

I've seen solutions where you simply accept all certificates, but what if I want to ask the user?

I want to get a dialog similar to that of the browser, letting the user decide to continue or not. Preferably I'd like to use the same certificatestore as the browser. Any ideas?

2018/02/20
1
154
2/20/2018 7:03:09 PM

Accepted Answer

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Although the method setHostnameVerifier() is obsolete for new library apache, but for version in Android SDK is normal.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);
2012/12/11
171
12/11/2012 8:57:42 AM


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

2014/05/16

I was frustrated trying to connect my Android App to my RESTful service using https. Also I was a bit annoyed about all the answers that suggested to disable certificate checking altogether. If you do so, whats the point of https?

After googled about the topic for a while, I finally found this solution where external jars are not needed, just Android APIs. Thanks to Andrew Smith, who posted it on July, 2014

 /**
 * Set up a connection to myservice.domain using HTTPS. An entire function
 * is needed to do this because myservice.domain has a self-signed certificate.
 * 
 * The caller of the function would do something like:
 * HttpsURLConnection urlConnection = setUpHttpsConnection("https://littlesvr.ca");
 * InputStream in = urlConnection.getInputStream();
 * And read from that "in" as usual in Java
 * 
 * Based on code from:
 * https://developer.android.com/training/articles/security-ssl.html#SelfSigned
 */
public static HttpsURLConnection setUpHttpsConnection(String urlString)
{
    try
    {
        // Load CAs from an InputStream
        // (could be from a resource or ByteArrayInputStream or ...)
        CertificateFactory cf = CertificateFactory.getInstance("X.509");

        // My CRT file that I put in the assets folder
        // I got this file by following these steps:
        // * Go to https://littlesvr.ca using Firefox
        // * Click the padlock/More/Security/View Certificate/Details/Export
        // * Saved the file as littlesvr.crt (type X.509 Certificate (PEM))
        // The MainActivity.context is declared as:
        // public static Context context;
        // And initialized in MainActivity.onCreate() as:
        // MainActivity.context = getApplicationContext();
        InputStream caInput = new BufferedInputStream(MainActivity.context.getAssets().open("littlesvr.crt"));
        Certificate ca = cf.generateCertificate(caInput);
        System.out.println("ca=" + ((X509Certificate) ca).getSubjectDN());

        // Create a KeyStore containing our trusted CAs
        String keyStoreType = KeyStore.getDefaultType();
        KeyStore keyStore = KeyStore.getInstance(keyStoreType);
        keyStore.load(null, null);
        keyStore.setCertificateEntry("ca", ca);

        // 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 context = SSLContext.getInstance("TLS");
        context.init(null, tmf.getTrustManagers(), null);

        // Tell the URLConnection to use a SocketFactory from our SSLContext
        URL url = new URL(urlString);
        HttpsURLConnection urlConnection = (HttpsURLConnection)url.openConnection();
        urlConnection.setSSLSocketFactory(context.getSocketFactory());

        return urlConnection;
    }
    catch (Exception ex)
    {
        Log.e(TAG, "Failed to establish SSL connection to server: " + ex.toString());
        return null;
    }
}

It worked nice for my mockup App.

2016/01/28

The top answer didn´t work for me. After some investigation I found the required information on "Android Developer": https://developer.android.com/training/articles/security-ssl.html#SelfSigned

Creating an empty implementation of X509TrustManager did the trick:

private static class MyTrustManager implements X509TrustManager
{

    @Override
    public void checkClientTrusted(X509Certificate[] chain, String authType)
         throws CertificateException
    {
    }

    @Override
    public void checkServerTrusted(X509Certificate[] chain, String authType)
        throws CertificateException
    {
    }

    @Override
    public X509Certificate[] getAcceptedIssuers()
    {
        return null;
    }

}

...

HttpsURLConnection conn = (HttpsURLConnection) url.openConnection();
try
{
    // Create an SSLContext that uses our TrustManager
    SSLContext context = SSLContext.getInstance("TLS");
    TrustManager[] tmlist = {new MyTrustManager()};
    context.init(null, tmlist, null);
    conn.setSSLSocketFactory(context.getSocketFactory());
}
catch (NoSuchAlgorithmException e)
{
    throw new IOException(e);
} catch (KeyManagementException e)
{
    throw new IOException(e);
}
conn.setRequestMethod("GET");
int rcode = conn.getResponseCode();

Please be aware that this empty implementation of TustManager is just an example and using it in a productive environment would cause a severe security threat!

2014/08/15

Google recommends the usage of Android Volley for HTTP/HTTPS connections, since that HttpClient is deprecated. So, you know the right choice :).

And also, NEVER NUKE SSL Certificates (NEVER!!!).

To nuke SSL Certificates, is totally against the purpose of SSL, which is promoting security. There's no sense of using SSL, if you're planning to bomb all SSL certificates that comes. A better solution would be, not using SSL, or a better solution, would be creating a custom TrustManager on your App + using Android Volley for HTTP/HTTPS connections.

Here's a Gist which I created, with a basic LoginApp, performing HTTPS connections, using a Self-Signed Certificate on the server-side, accepted on the App.

Here's also another Gist that may help, for creating Self-Signed SSL Certificates for setting up on your Server and also using the certificate on your App. Very important: you must copy the .crt file which was generated by the script above, to the "raw" directory from your Android project.

2018/02/20

Here's how you can add additional certificates to your KeyStore to avoid this problem: Trusting all certificates using HttpClient over HTTPS

It won't prompt the user like you ask, but it will make it less likely that the user will run into a "Not trusted server certificate" error.

2017/05/23

Source: https://stackoverflow.com/questions/2012497
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