Check in the onReceivedSslError() method of a WebViewClient if a certificate is signed from a specific self-signed CA

Question

I would like to override the onReceivedSslError() of a WebViewClient . Here I want to check if the error.getCertificate() certificate is signed from a self-signed CA and, only in this case , call the handler.proceed() . In pseudo-code:

@Override
public void onReceivedSslError(WebView view, SslErrorHandler handler, SslError error) {
    SslCertificate serverCertificate = error.getCertificate();

    if (/* signed from my self-signed CA */) {
        handler.proceed();
    }
    else {
        super.onReceivedSslError(view, handler, error);
    }
}

The public key of my CA is saved in a BouncyCastle resource called rootca.bks . How can I do?

Answer 1

I think you can try as the following:

@Override
protected void onCreate(Bundle savedInstanceState) {
    super.onCreate(savedInstanceState);
    setContentView(R.layout.activity_main);

    try {
        WebView webView = (WebView) findViewById(R.id.webView);
        if (webView != null) {
            // Get cert from raw resource...
            CertificateFactory cf = CertificateFactory.getInstance("X.509");
            InputStream caInput = getResources().openRawResource(R.raw.rootca); // stored at \app\src\main\res\raw
            final Certificate certificate = cf.generateCertificate(caInput);
            caInput.close();

            String url = "https://www.yourserver.com";
            webView.setWebViewClient(new WebViewClient() {                    
                @Override
                public void onReceivedSslError(WebView view, SslErrorHandler handler, SslError error) {
                    // Get cert from SslError
                    SslCertificate sslCertificate = error.getCertificate();
                    Certificate cert = getX509Certificate(sslCertificate);
                    if (cert != null && certificate != null){
                        try {
                            // Reference: https://developer.android.com/reference/java/security/cert/Certificate.html#verify(java.security.PublicKey)
                            cert.verify(certificate.getPublicKey()); // Verify here...
                            handler.proceed();
                        } catch (CertificateException | NoSuchAlgorithmException | InvalidKeyException | NoSuchProviderException | SignatureException e) {
                            super.onReceivedSslError(view, handler, error);
                            e.printStackTrace();
                        }
                    } else {
                        super.onReceivedSslError(view, handler, error);
                    }
                }
            });

            webView.loadUrl(url);
        }
    } catch (Exception e){
        e.printStackTrace();
    }
}

// credits to @Heath Borders at http://stackoverflow.com/questions/20228800/how-do-i-validate-an-android-net-http-sslcertificate-with-an-x509trustmanager
private Certificate getX509Certificate(SslCertificate sslCertificate){
    Bundle bundle = SslCertificate.saveState(sslCertificate);
    byte[] bytes = bundle.getByteArray("x509-certificate");
    if (bytes == null) {
        return null;
    } else {
        try {
            CertificateFactory certFactory = CertificateFactory.getInstance("X.509");
            return certFactory.generateCertificate(new ByteArrayInputStream(bytes));
        } catch (CertificateException e) {
            return null;
        }
    }
}

If failed validation, logcat will have some information such as java.security.SignatureException: Signature was not verified...

If success, here's a screenshot:

Answer 2

I think this should work ( SSL_IDMISMATCH means "Hostname mismatch").

@Override
public void onReceivedSslError(WebView view, SslErrorHandler handler, SslError error) {
    SslCertificate serverCertificate = error.getCertificate();

    if (error.hasError(SSL_UNTRUSTED)) {
        // Check if Cert-Domain equals the Uri-Domain
        String certDomain = serverCertificate.getIssuedTo().getCName();
        if(certDomain.equals(new URL(error.getUrl()).getHost())) {
          handler.proceed();
        }
    }
    else {
        super.onReceivedSslError(view, handler, error);
    }
}

If "hasError()" is not working, try error.getPrimaryError() == SSL_IDMISMATCH

Check Documentation of SslError for all error-types.

EDIT: I tested the function on my own self-cert server (its a Xampp), and I got Error #3. That means you have to check for error.hasError(SslError.SSL_UNTRUSTED) for a self-signed cert.

Answer 3

based on documentation:

Have you tried using the method getIssuedBy().getDName() of class SslCertificate. This method returns a String representing "The entity that issued this certificate".

Take a look here: http://developer.android.com/reference/android/net/http/SslCertificate.html#getIssuedBy()

Then you just need to know wich string is returned when it is self signed.

EDIT: I think that if it is selfsigned, that should return empty string, and if not, it would return the entity

Regards