android: added multi-factor authentication

wiki/android.md

@@ -9,3 +9,15 @@ It is designed primarily for mobile devices with touch screens like tablets or s
 The most used app store of android is the [Google Play Store](https://play.google.com/).
 A free and open-source alternative to it is [F-Droid](/wiki/android/f-droid.md) which only features
 open-source software.
+
+## Multi-Factor Authentication
+
+[Multi-factor authentication](/wiki/multi-factor_authentication.md) can easily be set up on android
+systems.
+For this the arguably most used app is
+[Google Authenticator](https://play.google.com/store/apps/details?id=com.google.android.apps.authenticator2&hl=de&gl=US).
+A free and open-source alternative for it is FreeOTP+.
+This app is available at [F-Droid](/wiki/android/f-droid.md) as
+[FreeOTP+](https://f-droid.org/de/packages/org.liberty.android.freeotpplus/) and on
+[Google Play Store](#app-store) by the
+[same name](https://f-droid.org/de/packages/org.liberty.android.freeotpplus/).

wiki/multi-factor_authentication.md

@@ -0,0 +1,12 @@
+# Multi-Factor Authentication
+
+Multi-factor authentication - most often two-factor authentication or 2FA - is an electronic
+authentication method that consists of having additional authentication mechanisms to the standard
+way which is most often a password.
+
+## Using the Smartphone as an Authentication Device
+
+Using Smartphones or other [smart devices](/wiki/smart_devices.md) is an easy way to set up
+multi-factor authentication because it is a device most people carry with them day by day.
+For setting it up refer to the
+[corresponding section of the Android entry](/wiki/android.md#multi-factor-authentication).