libpinning is a standalone Android library project that facilitates certificate pinning for SSL connections from Android apps, in order to minimize dependence on Certificate Authorities.

CA signatures are necessary for general purpose network communication tools: things like web browsers, which connect to arbitrary network endpoints and have no advance knowledge of what the SSL certificates for those endpoint should look like.

Most mobile apps are not general purpose communication tools. Instead, they typically connect directly to a narrow set of backend services that the app's author either controls, or can predict ahead of time.

This creates an opportunity for app developers to sidestep the security problems inherent with Certificate Authorities. The best way is to throw CA certificates out the window entirely by signing your own endpoint certificates with your own offline signing certificate, which you then distribute with your app. See this blog post for examples of the no-CA technique.

Sometimes, however, that's not possible, and you need to continue using CA certificates for one reason or another. Perhaps the API endpoint is shared with a web browser's endpoint, for instance.

In that case, it's necessary to employ "pinning," which is simply the act of verifying that the certificate chain looks the way you know it should, even if it's signed by a CA. This prevents other CAs from being able to effectively create forged certificates for your domain, as with the many Comodo breaches, the DigiNotar breach, and the TurkTrust breach.

This library is designed to make pinning easier on Android. It's structured as an Android library project, so you can simply link it to your own project and begin.

Using a simple HttpsURLConnection with a PinningTrustManager:

// Define an array of pins.  One of these must be present
// in the certificate chain you receive.  A pin is a hex-encoded
// hash of a X.509 certificate's SubjectPublicKeyInfo. A pin can
// be generated using the provided pin.py script:
// python ./tools/pin.py certificate_file.pem
String[] pins                 = new String[] {"f30012bbc18c231ac1a44b788e410ce754182513"};
URL url                       = new URL("https://www.google.com");
HttpsURLConnection connection = PinningHelper.getPinnedHttpsURLConnection(context, pins, url);

return connection.getInputStream();

Using a simple ``HttpClientwith aPinningTrustManager`:

String[] pins         = new String[] {"f30012bbc18c231ac1a44b788e410ce754182513"};
HttpClient httpClient = PinningHelper.getPinnedHttpClient(context, pins);

HttpResponse response = httpClient.execute(new HttpGet("https://www.google.com/"));

It's also possible to work with PinningTrustManager and PinningSSLSocketFactory more directly:

String[] pins                 = new String[] {"40c5401d6f8cbaf08b00edefb1ee87d005b3b9cd"};
SchemeRegistry schemeRegistry = new SchemeRegistry();
schemeRegistry.register(new Scheme("http", PlainSocketFactory.getSocketFactory(), 80));
schemeRegistry.register(new Scheme("https", new PinningSSLSocketFactory(getContext() ,pins, 0), 443));

HttpParams httpParams                     = new BasicHttpParams();
ClientConnectionManager connectionManager = new ThreadSafeClientConnManager(httpParams, schemeRegistry);
DefaultHttpClient httpClient              = new DefaultHttpClient(connectionManager, httpParams);

HttpResponse response = httpClient.execute(new HttpGet("https://www.google.com/"));

Have a bug? Please create an issue here on GitHub!

https://github.com/moxie0/AndroidPinning/issues

Copyright 2011-2013 Moxie Marlinspike

Licensed under the GPLv3: http://www.gnu.org/licenses/gpl-3.0.html

Please contact me if this license doesn't work for you.