Fix codestyle and follow suggestions

src/main/java/com/owncloud/android/authentication/PassCodeManager.java

@@ -85,7 +85,7 @@ public class PassCodeManager {
 
         if (!sExemptOfPasscodeActivites.contains(activity.getClass()) && Build.VERSION.SDK_INT >=
                 Build.VERSION_CODES.M && deviceCredentialsShouldBeRequested() &&
-                !DeviceCredentialUtils.tryEncrypt()) {
+                !DeviceCredentialUtils.tryEncrypt(activity)) {
             Intent i = new Intent(MainApp.getAppContext(), RequestCredentialsActivity.class);
             i.setFlags(Intent.FLAG_ACTIVITY_REORDER_TO_FRONT);
             activity.startActivity(i);
@@ -138,6 +138,6 @@ public class PassCodeManager {
     private boolean deviceCredentialsAreEnabled() {
         SharedPreferences appPrefs = PreferenceManager
                 .getDefaultSharedPreferences(MainApp.getAppContext());
-        return (appPrefs.getBoolean(Preferences.PREFERENCE_USE_DEVICE_CREDENTIALS, false));
+        return appPrefs.getBoolean(Preferences.PREFERENCE_USE_DEVICE_CREDENTIALS, false);
     }
 }

src/main/java/com/owncloud/android/ui/activity/Preferences.java

@@ -857,15 +857,14 @@ public class Preferences extends PreferenceActivity
             }
         } else if (requestCode == ACTION_REQUEST_CODE_DAVDROID_SETUP && resultCode == RESULT_OK) {
             DisplayUtils.showSnackMessage(this, R.string.prefs_calendar_contacts_sync_setup_successful);
-        } else if (requestCode == ACTION_CONFIRM_DEVICE_CREDENTIALS && resultCode == RESULT_OK) {
-            if (Build.VERSION.SDK_INT >= Build.VERSION_CODES.M &&
-                    data.getBooleanExtra(RequestCredentialsActivity.KEY_CHECK_RESULT, false)) {
-                SharedPreferences.Editor appPrefs = PreferenceManager
-                        .getDefaultSharedPreferences(getApplicationContext()).edit();
-                appPrefs.putBoolean(PREFERENCE_USE_DEVICE_CREDENTIALS, false).apply();
-
-                DisplayUtils.showSnackMessage(this, R.string.credentials_disabled);
-            }
+        } else if (requestCode == ACTION_CONFIRM_DEVICE_CREDENTIALS && resultCode == RESULT_OK &&
+            Build.VERSION.SDK_INT >= Build.VERSION_CODES.M &&
+            data.getBooleanExtra(RequestCredentialsActivity.KEY_CHECK_RESULT, false)) {
+            SharedPreferences.Editor appPrefs = PreferenceManager
+                    .getDefaultSharedPreferences(getApplicationContext()).edit();
+            appPrefs.putBoolean(PREFERENCE_USE_DEVICE_CREDENTIALS, false).apply();
+
+            DisplayUtils.showSnackMessage(this, R.string.credentials_disabled);
         }
     }
 

src/main/java/com/owncloud/android/ui/activity/RequestCredentialsActivity.java

@@ -1,9 +1,30 @@
+/*
+ *  Nextcloud Android client application
+ *
+ *  @author Harikrishnan Rajan
+ *  Copyright (C) 2017
+ *  Copyright (C) 2017 Nextcloud GmbH.
+ *
+ *  This program is free software: you can redistribute it and/or modify
+ *  it under the terms of the GNU Affero General Public License version 3,
+ *  as published by the Free Software Foundation.
+ *
+ *  This program is distributed in the hope that it will be useful,
+ *  but WITHOUT ANY WARRANTY; without even the implied warranty of
+ *  MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
+ *  GNU Affero General Public License for more details.
+ *
+ *  You should have received a copy of the GNU Affero General Public License
+ *  along with this program. If not, see http://www.gnu.org/licenses/.
+ *
+ */
 package com.owncloud.android.ui.activity;
 
 import android.app.Activity;
 import android.app.KeyguardManager;
 import android.content.Context;
 import android.content.Intent;
+import android.os.Build;
 import android.support.annotation.RequiresApi;
 import android.widget.Toast;
 
@@ -15,7 +36,7 @@ import com.owncloud.android.utils.DeviceCredentialUtils;
 /**
  * Dummy activity that is used to handle the device's default authentication workflow.
  */
-@RequiresApi(value = 23)
+@RequiresApi(Build.VERSION_CODES.M)
 public class RequestCredentialsActivity extends Activity {
 
     private static final String TAG = RequestCredentialsActivity.class.getSimpleName();
@@ -27,7 +48,8 @@ public class RequestCredentialsActivity extends Activity {
     @Override
     protected void onActivityResult(int requestCode, int resultCode, Intent data) {
         if (requestCode == REQUEST_CODE_CONFIRM_DEVICE_CREDENTIALS) {
-            if (resultCode == Activity.RESULT_OK && DeviceCredentialUtils.tryEncrypt()) {
+            if (resultCode == Activity.RESULT_OK && DeviceCredentialUtils
+                    .tryEncrypt(getApplicationContext())) {
                 finishWithResult(true);
             } else {
                 Toast.makeText(this, R.string.default_credentials_wrong, Toast.LENGTH_SHORT).show();
@@ -40,7 +62,7 @@ public class RequestCredentialsActivity extends Activity {
     protected void onResume() {
         super.onResume();
         AnalyticsUtils.setCurrentScreenName(this, SCREEN_NAME, TAG);
-        DeviceCredentialUtils.createKey();
+        DeviceCredentialUtils.createKey(getApplicationContext());
         requestCredentials();
     }
 

src/main/java/com/owncloud/android/utils/DeviceCredentialUtils.java

@@ -1,14 +1,38 @@
+/*
+ *  Nextcloud Android client application
+ *
+ *  @author Harikrishnan Rajan
+ *  Copyright (C) 2017
+ *  Copyright (C) 2017 Nextcloud GmbH.
+ *
+ *  This program is free software: you can redistribute it and/or modify
+ *  it under the terms of the GNU Affero General Public License version 3,
+ *  as published by the Free Software Foundation.
+ *
+ *  This program is distributed in the hope that it will be useful,
+ *  but WITHOUT ANY WARRANTY; without even the implied warranty of
+ *  MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
+ *  GNU Affero General Public License for more details.
+ *
+ *  You should have received a copy of the GNU Affero General Public License
+ *  along with this program. If not, see http://www.gnu.org/licenses/.
+ *
+ */
 package com.owncloud.android.utils;
 
 import android.app.KeyguardManager;
 import android.content.Context;
+import android.os.Build;
 import android.security.keystore.KeyGenParameterSpec;
 import android.security.keystore.KeyProperties;
 import android.support.annotation.RequiresApi;
 
+import com.owncloud.android.R;
 import com.owncloud.android.lib.common.utils.Log_OC;
 
 import java.io.IOException;
+import java.nio.ByteBuffer;
+import java.nio.IntBuffer;
 import java.security.InvalidAlgorithmParameterException;
 import java.security.InvalidKeyException;
 import java.security.KeyStore;
@@ -28,15 +52,11 @@ import javax.crypto.SecretKey;
 /**
  * Utility class with methods for handling device credentials.
  */
-@RequiresApi(value = 23)
+@RequiresApi(Build.VERSION_CODES.M)
 public class DeviceCredentialUtils {
 
     private static final String TAG = DeviceCredentialUtils.class.getSimpleName();
 
-    /** Alias for our key in the Android Key Store. */
-    private static final String KEY_NAME = "Nextcloud";
-    private static final byte[] SECRET_BYTE_ARRAY = new byte[] {1, 2, 3, 4, 5, 6};
-
     private static final int AUTHENTICATION_DURATION_SECONDS = 30;
 
     private static final String ANDROID_KEY_STORE = "AndroidKeyStore";
@@ -56,8 +76,9 @@ public class DeviceCredentialUtils {
      * Creates a symmetric key in the Android Key Store which can only be used after the user has
      * authenticated with device credentials within the last X seconds.
      */
-    public static void createKey() {
+    public static void createKey(Context context) {
         // Generate a key to decrypt payment credentials, tokens, etc.
+        final String keyName = context.getResources().getString(R.string.secret_key_name);
         try {
             KeyStore keyStore = KeyStore.getInstance(ANDROID_KEY_STORE);
             keyStore.load(null);
@@ -66,7 +87,7 @@ public class DeviceCredentialUtils {
 
             // Set the alias of the entry in Android KeyStore where the key will appear
             // and the constrains (purposes) in the constructor of the Builder
-            keyGenerator.init(new KeyGenParameterSpec.Builder(KEY_NAME,
+            keyGenerator.init(new KeyGenParameterSpec.Builder(keyName,
                     KeyProperties.PURPOSE_ENCRYPT | KeyProperties.PURPOSE_DECRYPT)
                     .setBlockModes(KeyProperties.BLOCK_MODE_CBC)
                     .setUserAuthenticationRequired(true)
@@ -86,11 +107,17 @@ public class DeviceCredentialUtils {
      * Tries to encrypt some data with the generated key in {@link #createKey} which
      * only works if the user has just authenticated via device credentials.
      */
-    public static boolean tryEncrypt() {
+    public static boolean tryEncrypt(Context context) {
         try {
+            final String keyName = context.getResources().getString(R.string.secret_key_name);
+            final int[] secretIntArray = context.getResources().getIntArray(R.array.secret_byte_array);
+            ByteBuffer byteBuffer = ByteBuffer.allocate(secretIntArray.length * 4);
+            IntBuffer intBuffer = byteBuffer.asIntBuffer();
+            intBuffer.put(secretIntArray);
+            byte[] secretByteArray = byteBuffer.array();
             KeyStore keyStore = KeyStore.getInstance(ANDROID_KEY_STORE);
             keyStore.load(null);
-            SecretKey secretKey = (SecretKey) keyStore.getKey(KEY_NAME, null);
+            SecretKey secretKey = (SecretKey) keyStore.getKey(keyName, null);
             Cipher cipher = Cipher.getInstance(
                     KeyProperties.KEY_ALGORITHM_AES + "/" + KeyProperties.BLOCK_MODE_CBC + "/"
                             + KeyProperties.ENCRYPTION_PADDING_PKCS7);
@@ -98,7 +125,7 @@ public class DeviceCredentialUtils {
             // Try encrypting something, it will only work if the user authenticated within
             // the last AUTHENTICATION_DURATION_SECONDS seconds.
             cipher.init(Cipher.ENCRYPT_MODE, secretKey);
-            cipher.doFinal(SECRET_BYTE_ARRAY);
+            cipher.doFinal(secretByteArray);
 
             // If the user has recently authenticated, you will reach here.
             return true;

src/main/res/values/setup.xml

@@ -91,6 +91,15 @@
     <!-- Help, imprint and feedback, and other things -->
     <bool name="passcode_enabled">true</bool>
     <bool name="device_credentials_enabled">true</bool>
+    <string name="secret_key_name">Nextcloud</string>
+    <integer-array name="secret_byte_array">
+        <item>1</item>
+        <item>2</item>
+        <item>3</item>
+        <item>4</item>
+        <item>5</item>
+        <item>6</item>
+    </integer-array>
     <bool name="show_hidden_files_enabled">true</bool>
     <bool name="davdroid_integration_enabled">true</bool>
     <bool name="help_enabled">true</bool>