Xamarin.Android - Finger Print Authentication

Introduction

In this article, I’m going to show you exactly how to implement fingerprint authentication in your own apps, by walking you through the process of creating a sample app that registers when the user places their fingertip against their device’s touch sensor, processes their input, and then displays a range of toasts depending on whether the fingerprint authentication has succeeded or failed. We’ll also be looking at how to test fingerprint authentication on Android Virtual Devices (AVDs) that don’t feature a physical touch sensor.

The prerequisites

• Android Support Library v7 AppCompat
• Fingerprint Image

The steps given below are required to be followed in order to create a Fingerprint Authentication app in Xamarin.Android, using Visual Studio.

 

Step 1 - Creating Fingerprint Authentication Project

 

Let's create your Android solution in Visual Studio or Xamarin Studio. Select Android and from list choose Android Blank App give it a name like, FingerAuth.

 

Step 2 - Add Fingerprint to Emulator

 

First we will add our fingerprint to AVD - (I suggest you use Android Studio's Emulator for this example).

1. Go to your Emulator -> Settings -> Security -> FingerPrint -> Add -> Set your PIN (for example 1234) -> Next Find your Sensor.
   
   
2. Now go to Start and open Cmd as Administrator then change directory (cd) so it’s pointing at your Android SDK download; specifically, the Android/sdk/platform-tools folder.
   
   My command looks like this,
   
   cd C:\Program Files (x86)\Android\android-sdk\platform-tools
   
   
3. Add your frintprint by typing new cmd (adb -e emu finger touch 1234abc). In this example I am setting up fingerprint 1234abc.
   
   

Step 3 - Add Android Support v7 AppCompat Library

 

First of all, in References add a reference Android.Support.v7. AppCompat using NuGet Package Manager, as shown below.

 

 

 

Step 4 - Add Finger Print Image

 

Open Solution Explorer -> Project Name -> Resources-> Drawable. Fingerprint image paste into drawable folder.

 

 

Step 5 - Add XML File

 

After successful installation of AppCompat, add a new XML file. For that, go to Solution Explorer-> Project Name-> Resources-> Values-> Right-click to add a new item, select XML, and give it a name, such as Styles.xml. Open this XML file and add the following code.

 

(Folder Name: values, File Name: Styles.xml)

 

XML Code

<?xml version="1.0" encoding="utf-8" ?>
<resources>
<style name="AppTheme" parent="Theme.AppCompat.Light.NoActionBar">
  <item name="colorPrimary">#263237</item>
  <item name="colorPrimaryDark">#263237</item>
  <item name="colorAccent">#1e282d</item>
</style>
</resources>

Step 6 - Main Layout

 

Open Solution Explorer-> Project Name-> Resources-> Layout-> Main.axml. Open this main layout file and add the following code.

 

(File Name: Main.axml , Folder Name: Layout)

 

XML Code

<?xml version="1.0" encoding="utf-8"?>
<RelativeLayout xmlns:android="http://schemas.android.com/apk/res/android"
    android:layout_width="match_parent"
    android:layout_height="match_parent"
    android:background="#263237"
    android:padding="16dp">
    <ImageView
        android:id="@+id/fingerImage"
        android:src="@drawable/fingerprint"
        android:layout_centerInParent="true"
        android:layout_width="150dp"
        android:layout_height="150dp" />
    <TextView
        android:layout_below="@+id/fingerImage"
        android:textColor="#F5F5F5"
        android:textSize="20sp"
        android:text="Please place your fingertip on the scanner to verify your identity"
        android:layout_centerHorizontal="true"
        android:textAlignment="center"
        android:layout_width="wrap_content"
        android:layout_height="wrap_content" />
</RelativeLayout>

Step 7 - Add Home Layout

 

Next, add a new layout by going to Solution Explorer-> Project Name-> Resources-> Layout. Right-click to add a new item, select Layout, and give it a name, such as Home.axml. Open this layout file and add the following code.

 

(Folder Name: Layout , File Name: Home.axml)

 

XML Code

<?xml version="1.0" encoding="utf-8"?>
<RelativeLayout xmlns:android="http://schemas.android.com/apk/res/android"
    android:padding="16dp"
    android:layout_width="match_parent"
    android:layout_height="match_parent">
    <TextView
        android:textColor="#95aab4"
        android:textSize="20sp"
        android:text="You have successfully logged in with Fingerprint Authentication"
        android:layout_centerHorizontal="true"
        android:textAlignment="center"
        android:layout_width="wrap_content"
        android:layout_height="wrap_content" />
</RelativeLayout>

Step 8 - Create Home Activity

 

Add a new Activity. For this, open Solution Explorer-> Project Name-> right click to add a new item and select Activity. Give it a name like Home and add the following code putting appropriate namespaces.

 

(FileName: Home)

 

C# Code

using Android.App;
using Android.OS;
using Android.Support.V7.App;
namespace FingerAuth
{
    [Activity(Label = "HomeActivity" , Theme ="@style/AppTheme")]
    public class HomeActivity : AppCompatActivity
    {
        protected override void OnCreate(Bundle savedInstanceState)
        {
            base.OnCreate(savedInstanceState);
            // Create your application here
            SetContentView(Resource.Layout.Home);
        }
    }
}

Step 9 - Main Activity Class

 

Now, go to Solution Explorer-> Project Name-> MainActivity and add the following code with appropriate namespaces.

 

(FileName: MainActivity)

 

C# Code

using Android.App;
using Android.Widget;
using Android.OS;
using Android.Support.V7.App;
using Java.Security;
using Javax.Crypto;
using Android.Hardware.Fingerprints;
using Android.Support.V4.App;
using Android;
using System;
using Android.Security.Keystore;
namespace FingerAuth
{
    [Activity(Label = "FingerAuth", MainLauncher = true, Theme ="@style/AppTheme")]
    public class MainActivity : AppCompatActivity
    {
        private KeyStore keyStore;
        private Cipher cipher;
        private string KEY_NAME = "Ahsan";
        protected override void OnCreate(Bundle savedInstanceState)
        {
            base.OnCreate(savedInstanceState);
            // Set our view from the "main" layout resource
            SetContentView(Resource.Layout.Main);
            KeyguardManager keyguardManager = (KeyguardManager)GetSystemService(KeyguardService);
            FingerprintManager fingerprintManager = (FingerprintManager)GetSystemService(FingerprintService);
            if (ActivityCompat.CheckSelfPermission(this, Manifest.Permission.UseFingerprint)
                != (int)Android.Content.PM.Permission.Granted)
                return;
            if (!fingerprintManager.IsHardwareDetected)
                Toast.MakeText(this, "FingerPrint authentication permission not enable", ToastLength.Short).Show();
            else
            {
                if(!fingerprintManager.HasEnrolledFingerprints)
                    Toast.MakeText(this, "Register at least one fingerprint in Settings", ToastLength.Short).Show();
                else
                {
                    if (!keyguardManager.IsKeyguardSecure)
                        Toast.MakeText(this, "Lock screen security not enable in Settings", ToastLength.Short).Show();
                    else
                        GenKey();
                    if (CipherInit())
                    {
                        FingerprintManager.CryptoObject cryptoObject = new FingerprintManager.CryptoObject(cipher);
                        FingerprintHandler handler = new FingerprintHandler(this);
                        handler.StartAuthentication(fingerprintManager, cryptoObject);
                    }
                }
            }
        }
        private bool CipherInit()
        {
            try
            {
                cipher = Cipher.GetInstance(KeyProperties.KeyAlgorithmAes
                    + "/"
                    + KeyProperties.BlockModeCbc
                    + "/"
                    + KeyProperties.EncryptionPaddingPkcs7);
                keyStore.Load(null);
                IKey key = (IKey)keyStore.GetKey(KEY_NAME, null);
                cipher.Init(CipherMode.EncryptMode, key);
                return true;
            }
            catch(Exception ex) { return false; }
        }
        private void GenKey()
        {
            keyStore = KeyStore.GetInstance("AndroidKeyStore");
            KeyGenerator keyGenerator = null;
            keyGenerator = KeyGenerator.GetInstance(KeyProperties.KeyAlgorithmAes, "AndroidKeyStore");
            keyStore.Load(null);
            keyGenerator.Init(new KeyGenParameterSpec.Builder(KEY_NAME, KeyStorePurpose.Encrypt | KeyStorePurpose.Decrypt)
                .SetBlockModes(KeyProperties.BlockModeCbc)
                .SetUserAuthenticationRequired(true)
                .SetEncryptionPaddings(KeyProperties
                .EncryptionPaddingPkcs7).Build());
            keyGenerator.GenerateKey();
        }
    }
}

Step 10 - Writing FingerprintHandler Class

 

Go to Solution Explorer-> Project Name and right-click. Select Add -> New Item-> Class. Give it a name like FingerprintHandler.cs and write the following code with appropriate namespaces.

 

(File Name: FingerprintHandler.cs)

 

C# Code

using System;
using Android;
using Android.Content;
using Android.Hardware.Fingerprints;
using Android.OS;
using Android.Support.V4.App;
using Android.Widget;
namespace FingerAuth
{
    internal class FingerprintHandler : FingerprintManager.AuthenticationCallback
    {
        private Context mainActivity;
        public FingerprintHandler(Context mainActivity)
        {
            this.mainActivity = mainActivity;
        }
        internal void StartAuthentication(FingerprintManager fingerprintManager, FingerprintManager.CryptoObject cryptoObject)
        {
            CancellationSignal cancellationSignal = new CancellationSignal();
            if (ActivityCompat.CheckSelfPermission(mainActivity, Manifest.Permission.UseFingerprint)
                != (int)Android.Content.PM.Permission.Granted)
                return;
            fingerprintManager.Authenticate(cryptoObject, cancellationSignal, 0, this, null);
        }
        public override void OnAuthenticationFailed()
        {
            Toast.MakeText(mainActivity, "Fingerprint Authentication failed!",ToastLength.Long).Show();
        }
        public override void OnAuthenticationSucceeded(FingerprintManager.AuthenticationResult result)
        {
            mainActivity.StartActivity(new Intent(mainActivity, typeof(HomeActivity)));
        }
    }
}

Step 10 - Permission From Device

 

We need a permission from the device because we shall be using the device’s finger print. Please add Fingerprint permission to your AndroidManifest.xml.Let's open Solution Explorer-> Properties-> AndroidManifest and let's add the code inside application tags.

<uses-permission android:name="android.permission.USE_FINGERPRINT" /> 

 

Output 

 

 

 

Summary

 

This was the process of creating a Fingerprint Auth app in Xamarin.Android, using Visual Studio. Please share your comments and feedback.