How to install trusted CA certificate on Android device?

I spent a lot of time trying to find an answer to this (I need Android to see StartSSL certificates). Conclusion: Android 2.1 and 2.2 allow you to import certificates, but only for use with WiFi and VPN. There is no user interface for updating the list of trusted root certificates, but there is discussion about adding that feature. It’s unclear whether there is a reliable workaround for manually updating and replacing the cacerts.bks file.

Details and links: http://www.mcbsys.com/techblog/2010/12/android-certificates/. In that post, see the link to Android bug 11231--you might want to add your vote and query to that bug.

If you need your certificate for HTTPS connections you can add the .bks file as a raw resource to your application and extend DefaultHttpConnection so your certificates are used for HTTPS connections.

public class MyHttpClient extends DefaultHttpClient {

    private Resources _resources;

    public MyHttpClient(Resources resources) {
        _resources = resources;
    }

    @Override
    protected ClientConnectionManager createClientConnectionManager() {
        SchemeRegistry registry = new SchemeRegistry();
        registry.register(new Scheme("http", PlainSocketFactory
            .getSocketFactory(), 80));
        if (_resources != null) {
            registry.register(new Scheme("https", newSslSocketFactory(), 443));
        } else {
            registry.register(new Scheme("https", SSLSocketFactory
                .getSocketFactory(), 443));
        }
        return new SingleClientConnManager(getParams(), registry);
    }

    private SSLSocketFactory newSslSocketFactory() {
        try {
            KeyStore trusted = KeyStore.getInstance("BKS");
            InputStream in = _resources.openRawResource(R.raw.mystore);
            try {
                trusted.load(in, "pwd".toCharArray());
            } finally {
                in.close();
            }
            return new SSLSocketFactory(trusted);
        } catch (Exception e) {
            throw new AssertionError(e);
        }
    }
}

Prior to Android KitKat you have to root your device to install new certificates.

From Android KitKat (4.0) up to Marshmallow (6.0) it's possible and easy. I was able to install the Charles Web Debbuging Proxy cert on my un-rooted device and successfully sniff SSL traffic.

Extract from http://wiki.cacert.org/FAQ/ImportRootCert

Before Android version 4.0, with Android version Gingerbread & Froyo, there was a single read-only file ( /system/etc/security/cacerts.bks ) containing the trust store with all the CA ('system') certificates trusted by default on Android. Both system apps and all applications developed with the Android SDK use this. Use these instructions on installing CAcert certificates on Android Gingerbread, Froyo, ...

Starting from Android 4.0 (Android ICS/'Ice Cream Sandwich', Android 4.3 'Jelly Bean' & Android 4.4 'KitKat'), system trusted certificates are on the (read-only) system partition in the folder '/system/etc/security/' as individual files. However, users can now easily add their own 'user' certificates which will be stored in '/data/misc/keychain/certs-added'.

System-installed certificates can be managed on the Android device in the Settings -> Security -> Certificates -> 'System'-section, whereas the user trusted certificates are manged in the 'User'-section there. When using user trusted certificates, Android will force the user of the Android device to implement additional safety measures: the use of a PIN-code, a pattern-lock or a password to unlock the device are mandatory when user-supplied certificates are used.

Installing CAcert certificates as 'user trusted'-certificates is very easy. Installing new certificates as 'system trusted'-certificates requires more work (and requires root access), but it has the advantage of avoiding the Android lockscreen requirement.

From Android N (7.0) onwards it gets a littler harder, see this extract from the Charles proxy website:

As of Android N, you need to add configuration to your app in order to have it trust the SSL certificates generated by Charles SSL Proxying. This means that you can only use SSL Proxying with apps that you control.

In order to configure your app to trust Charles, you need to add a Network Security Configuration File to your app. This file can override the system default, enabling your app to trust user installed CA certificates (e.g. the Charles Root Certificate). You can specify that this only applies in debug builds of your application, so that production builds use the default trust profile.

Add a file res/xml/network_security_config.xml to your app:

<network-security-config>    
    <debug-overrides> 
        <trust-anchors> 
            <!-- Trust user added CAs while debuggable only -->
            <certificates src="user" /> 
        </trust-anchors>    
    </debug-overrides>  
</network-security-config>

Then add a reference to this file in your app's manifest, as follows:

<?xml version="1.0" encoding="utf-8"?> 
<manifest>
    <application android:networkSecurityConfig="@xml/network_security_config">
    </application> 
</manifest>