How to install trusted CA certificate on Android device?

Question

I have created my own CA certificate and now I want to install it on my Android Froyo device (HTC Desire Z), so that the device trusts my certificate.

Android stores CA certificates in its Java keystore in /system/etc/security/cacerts.bks. I copied the file to my computer, added my certificate using portecle 1.5 and pushed it back to the device.

Now, Android does not seem to reload the file automatically. I have read in several blog posts that I need to restart the device. Doing so results in the file being overwritten with the original one again.

My next try was to install the certificate from SD card by copying it and using the according option from the settings menu. The device tells me that the certificate has been installed, but apparently it does not trust the certificate. Moreover, when I try to copy the keystore to my computer, I still find the original stock cacerts.bks.

So, what is the right way to install my own root CA certificate on an Android 2.2 device as a trusted certificate? Is there a way to do it programmatically?

Answer 1

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

From Android KitKat (4.0) up to Nougat (7.0) 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 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>