diff --git a/OpenPGP-Keychain/res/layout/api_app_settings_fragment.xml b/OpenPGP-Keychain/res/layout/api_app_settings_fragment.xml
index 81b48be72..a40444e0f 100644
--- a/OpenPGP-Keychain/res/layout/api_app_settings_fragment.xml
+++ b/OpenPGP-Keychain/res/layout/api_app_settings_fragment.xml
@@ -1,122 +1,153 @@
 <?xml version="1.0" encoding="utf-8"?>
-<LinearLayout xmlns:android="http://schemas.android.com/apk/res/android"
-    android:layout_width="fill_parent"
-    android:layout_height="fill_parent"
-    android:orientation="vertical" >
-
-    <RelativeLayout
-        android:layout_width="match_parent"
-        android:layout_height="?android:attr/listPreferredItemHeight"
-        android:gravity="center_horizontal"
-        android:orientation="horizontal"
-        android:paddingBottom="3dip" >
-
-        <ImageView
-            android:id="@+id/api_app_settings_app_icon"
-            android:layout_width="48dp"
-            android:layout_height="48dp"
-            android:layout_alignParentBottom="true"
-            android:layout_alignParentTop="true"
-            android:layout_marginRight="6dp"
-            android:src="@drawable/icon" />
-
-        <TextView
-            android:id="@+id/api_app_settings_app_name"
-            android:layout_width="wrap_content"
-            android:layout_height="wrap_content"
-            android:layout_centerVertical="true"
-            android:layout_toRightOf="@+id/api_app_settings_app_icon"
-            android:gravity="center_vertical"
-            android:orientation="vertical"
-            android:text="Name (set in-code)"
-            android:textAppearance="?android:attr/textAppearanceMedium" />
-    </RelativeLayout>
+<ScrollView xmlns:android="http://schemas.android.com/apk/res/android"
+    android:layout_width="match_parent"
+    android:layout_height="wrap_content" >
 
     <LinearLayout
-        android:layout_width="fill_parent"
+        android:layout_width="match_parent"
         android:layout_height="wrap_content"
-        android:orientation="horizontal" >
+        android:orientation="vertical" >
 
-        <Button
-            android:id="@+id/api_app_settings_select_key_button"
-            android:layout_width="wrap_content"
-            android:layout_height="wrap_content"
-            android:layout_gravity="center_vertical"
-            android:text="@string/api_settings_select_key" />
+        <RelativeLayout
+            android:layout_width="match_parent"
+            android:layout_height="?android:attr/listPreferredItemHeight"
+            android:gravity="center_horizontal"
+            android:orientation="horizontal"
+            android:paddingBottom="3dip" >
 
-        <LinearLayout
-            android:layout_width="fill_parent"
-            android:layout_height="wrap_content"
-            android:orientation="vertical"
-            android:paddingLeft="16dp" >
+            <ImageView
+                android:id="@+id/api_app_settings_app_icon"
+                android:layout_width="48dp"
+                android:layout_height="48dp"
+                android:layout_alignParentBottom="true"
+                android:layout_alignParentTop="true"
+                android:layout_marginRight="6dp"
+                android:src="@drawable/icon" />
 
             <TextView
-                android:id="@+id/api_app_settings_user_id"
+                android:id="@+id/api_app_settings_app_name"
                 android:layout_width="wrap_content"
                 android:layout_height="wrap_content"
-                android:layout_gravity="right"
-                android:ellipsize="end"
-                android:singleLine="true"
-                android:text="@string/api_settings_no_key"
+                android:layout_centerVertical="true"
+                android:layout_toRightOf="@+id/api_app_settings_app_icon"
+                android:gravity="center_vertical"
+                android:orientation="vertical"
+                android:text="Name (set in-code)"
+                android:textAppearance="?android:attr/textAppearanceMedium" />
+        </RelativeLayout>
+
+        <LinearLayout
+            android:layout_width="match_parent"
+            android:layout_height="wrap_content"
+            android:orientation="horizontal" >
+
+            <Button
+                android:id="@+id/api_app_settings_select_key_button"
+                android:layout_width="wrap_content"
+                android:layout_height="wrap_content"
+                android:layout_gravity="center_vertical"
+                android:text="@string/api_settings_select_key" />
+
+            <LinearLayout
+                android:layout_width="match_parent"
+                android:layout_height="wrap_content"
+                android:orientation="vertical"
+                android:paddingLeft="16dp" >
+
+                <TextView
+                    android:id="@+id/api_app_settings_user_id"
+                    android:layout_width="wrap_content"
+                    android:layout_height="wrap_content"
+                    android:layout_gravity="right"
+                    android:ellipsize="end"
+                    android:singleLine="true"
+                    android:text="@string/api_settings_no_key"
+                    android:textAppearance="?android:attr/textAppearanceMedium" />
+
+                <TextView
+                    android:id="@+id/api_app_settings_user_id_rest"
+                    android:layout_width="wrap_content"
+                    android:layout_height="wrap_content"
+                    android:layout_gravity="right"
+                    android:ellipsize="end"
+                    android:singleLine="true"
+                    android:text=""
+                    android:textAppearance="?android:attr/textAppearanceSmall" />
+            </LinearLayout>
+        </LinearLayout>
+
+        <Button
+            android:id="@+id/api_app_settings_advanced_button"
+            android:layout_width="match_parent"
+            android:layout_height="wrap_content"
+            android:text="@string/api_settings_show_advanced" />
+
+        <LinearLayout
+            android:id="@+id/api_app_settings_advanced"
+            android:layout_width="match_parent"
+            android:layout_height="wrap_content"
+            android:orientation="vertical"
+            android:visibility="gone" >
+
+            <TextView
+                android:layout_width="match_parent"
+                android:layout_height="wrap_content"
+                android:text="@string/label_encryption_algorithm"
+                android:textAppearance="?android:attr/textAppearanceMedium" />
+
+            <Spinner
+                android:id="@+id/api_app_settings_encryption_algorithm"
+                android:layout_width="match_parent"
+                android:layout_height="wrap_content" />
+
+            <TextView
+                android:layout_width="match_parent"
+                android:layout_height="wrap_content"
+                android:text="@string/label_hash_algorithm"
+                android:textAppearance="?android:attr/textAppearanceMedium" />
+
+            <Spinner
+                android:id="@+id/api_app_settings_hash_algorithm"
+                android:layout_width="match_parent"
+                android:layout_height="wrap_content" />
+
+            <TextView
+                android:layout_width="match_parent"
+                android:layout_height="wrap_content"
+                android:text="@string/label_message_compression"
+                android:textAppearance="?android:attr/textAppearanceMedium" />
+
+            <Spinner
+                android:id="@+id/api_app_settings_compression"
+                android:layout_width="match_parent"
+                android:layout_height="wrap_content" />
+
+            <TextView
+                android:layout_width="match_parent"
+                android:layout_height="wrap_content"
+                android:text="@string/api_settings_package_name"
                 android:textAppearance="?android:attr/textAppearanceMedium" />
 
             <TextView
-                android:id="@+id/api_app_settings_user_id_rest"
-                android:layout_width="wrap_content"
+                android:id="@+id/api_app_settings_package_name"
+                android:layout_width="match_parent"
                 android:layout_height="wrap_content"
-                android:layout_gravity="right"
-                android:ellipsize="end"
-                android:singleLine="true"
-                android:text=""
+                android:text="com.example"
+                android:textAppearance="?android:attr/textAppearanceMedium" />
+
+            <TextView
+                android:layout_width="match_parent"
+                android:layout_height="wrap_content"
+                android:text="@string/api_settings_package_signature"
+                android:textAppearance="?android:attr/textAppearanceMedium" />
+
+            <TextView
+                android:id="@+id/api_app_settings_package_signature"
+                android:layout_width="match_parent"
+                android:layout_height="wrap_content"
+                android:text="Base64 encoded signature"
                 android:textAppearance="?android:attr/textAppearanceSmall" />
         </LinearLayout>
     </LinearLayout>
 
-    <Button
-        android:id="@+id/api_app_settings_advanced_button"
-        android:layout_width="match_parent"
-        android:layout_height="wrap_content"
-        android:text="@string/api_settings_show_advanced" />
-
-    <LinearLayout
-        android:id="@+id/api_app_settings_advanced"
-        android:layout_width="fill_parent"
-        android:layout_height="wrap_content"
-        android:orientation="vertical"
-        android:visibility="invisible" >
-
-        <TextView
-            android:layout_width="match_parent"
-            android:layout_height="wrap_content"
-            android:text="@string/label_encryption_algorithm"
-            android:textAppearance="?android:attr/textAppearanceMedium" />
-
-        <Spinner
-            android:id="@+id/api_app_settings_encryption_algorithm"
-            android:layout_width="match_parent"
-            android:layout_height="wrap_content" />
-
-        <TextView
-            android:layout_width="match_parent"
-            android:layout_height="wrap_content"
-            android:text="@string/label_hash_algorithm"
-            android:textAppearance="?android:attr/textAppearanceMedium" />
-
-        <Spinner
-            android:id="@+id/api_app_settings_hash_algorithm"
-            android:layout_width="match_parent"
-            android:layout_height="wrap_content" />
-
-        <TextView
-            android:layout_width="match_parent"
-            android:layout_height="wrap_content"
-            android:text="@string/label_message_compression"
-            android:textAppearance="?android:attr/textAppearanceMedium" />
-
-        <Spinner
-            android:id="@+id/api_app_settings_compression"
-            android:layout_width="match_parent"
-            android:layout_height="wrap_content" />
-    </LinearLayout>
-
-</LinearLayout>
\ No newline at end of file
+</ScrollView>
\ No newline at end of file
diff --git a/OpenPGP-Keychain/res/values/strings.xml b/OpenPGP-Keychain/res/values/strings.xml
index 63f267277..da82e7553 100644
--- a/OpenPGP-Keychain/res/values/strings.xml
+++ b/OpenPGP-Keychain/res/values/strings.xml
@@ -313,7 +313,7 @@
     <string name="import_qr_code_missing">Missing QR Codes: %1$s</string>
     <string name="import_qr_code_wrong">QR Code malformed! Please try again!</string>
     <string name="import_qr_code_finished">QR Code scanning finished!</string>
-    
+
     <!-- Intent labels -->
     <string name="intent_decrypt_file">OpenPGP: Decrypt File</string>
     <string name="intent_import_key">OpenPGP: Import Key</string>
@@ -329,6 +329,8 @@
     <string name="api_settings_save">Save</string>
     <string name="api_settings_cancel">Cancel</string>
     <string name="api_settings_revoke">Revoke access</string>
+    <string name="api_settings_package_name">Package Name</string>
+    <string name="api_settings_package_signature">SHA-256 of Package Signature</string>
     <string name="api_register_text">The following application requests access to OpenPGP Keychain\'s API.\n\nAllow permanent access?</string>
     <string name="api_register_allow">Allow access</string>
     <string name="api_register_disallow">Disallow access</string>
diff --git a/OpenPGP-Keychain/src/org/openintents/openpgp/IOpenPgpService.aidl b/OpenPGP-Keychain/src/org/openintents/openpgp/IOpenPgpService.aidl
index 7cbf96b56..8f9e8a0fd 100644
--- a/OpenPGP-Keychain/src/org/openintents/openpgp/IOpenPgpService.aidl
+++ b/OpenPGP-Keychain/src/org/openintents/openpgp/IOpenPgpService.aidl
@@ -50,7 +50,6 @@ interface IOpenPgpService {
      */
     oneway void sign(in OpenPgpData input, in OpenPgpData output, in IOpenPgpCallback callback);
     
-    
     /**
      * Encrypt
      * 
diff --git a/OpenPGP-Keychain/src/org/openintents/openpgp/OpenPgpConstants.java b/OpenPGP-Keychain/src/org/openintents/openpgp/OpenPgpConstants.java
new file mode 100644
index 000000000..b1ca1bfe6
--- /dev/null
+++ b/OpenPGP-Keychain/src/org/openintents/openpgp/OpenPgpConstants.java
@@ -0,0 +1,10 @@
+package org.openintents.openpgp;
+
+public class OpenPgpConstants {
+
+    public static final String TAG = "OpenPgp API";
+
+    public static final int REQUIRED_API_VERSION = 1;
+    public static final String SERVICE_INTENT = "org.openintents.openpgp.IOpenPgpService";
+
+}
diff --git a/OpenPGP-Keychain/src/org/openintents/openpgp/OpenPgpHelper.java b/OpenPGP-Keychain/src/org/openintents/openpgp/OpenPgpHelper.java
index 56c4a4dca..7305c47ce 100644
--- a/OpenPGP-Keychain/src/org/openintents/openpgp/OpenPgpHelper.java
+++ b/OpenPGP-Keychain/src/org/openintents/openpgp/OpenPgpHelper.java
@@ -40,7 +40,7 @@ public class OpenPgpHelper {
     }
 
     public boolean isAvailable() {
-        Intent intent = new Intent(IOpenPgpService.class.getName());
+        Intent intent = new Intent(OpenPgpConstants.SERVICE_INTENT);
         List<ResolveInfo> resInfo = context.getPackageManager().queryIntentServices(intent, 0);
         if (!resInfo.isEmpty()) {
             return true;
diff --git a/OpenPGP-Keychain/src/org/openintents/openpgp/OpenPgpListPreference.java b/OpenPGP-Keychain/src/org/openintents/openpgp/OpenPgpListPreference.java
index 551401b18..4fef3f32c 100644
--- a/OpenPGP-Keychain/src/org/openintents/openpgp/OpenPgpListPreference.java
+++ b/OpenPGP-Keychain/src/org/openintents/openpgp/OpenPgpListPreference.java
@@ -39,22 +39,19 @@ public class OpenPgpListPreference extends DialogPreference {
     ArrayList<OpenPgpProviderEntry> mProviderList = new ArrayList<OpenPgpProviderEntry>();
     private String mSelectedPackage;
 
-    public static final int REQUIRED_API_VERSION = 1;
-
     public OpenPgpListPreference(Context context, AttributeSet attrs) {
         super(context, attrs);
 
-        List<ResolveInfo> resInfo =
-                context.getPackageManager().queryIntentServices(
-                        new Intent(IOpenPgpService.class.getName()), PackageManager.GET_META_DATA);
+        List<ResolveInfo> resInfo = context.getPackageManager().queryIntentServices(
+                new Intent(OpenPgpConstants.SERVICE_INTENT), PackageManager.GET_META_DATA);
         if (!resInfo.isEmpty()) {
             for (ResolveInfo resolveInfo : resInfo) {
                 if (resolveInfo.serviceInfo == null)
                     continue;
 
                 String packageName = resolveInfo.serviceInfo.packageName;
-                String simpleName = String.valueOf(resolveInfo.serviceInfo
-                        .loadLabel(context.getPackageManager()));
+                String simpleName = String.valueOf(resolveInfo.serviceInfo.loadLabel(context
+                        .getPackageManager()));
                 Drawable icon = resolveInfo.serviceInfo.loadIcon(context.getPackageManager());
 
                 // get api version
@@ -95,8 +92,8 @@ public class OpenPgpListPreference extends DialogPreference {
                 TextView tv = (TextView) v.findViewById(android.R.id.text1);
 
                 // Put the image on the TextView
-                tv.setCompoundDrawablesWithIntrinsicBounds(mProviderList.get(position).icon,
-                        null, null, null);
+                tv.setCompoundDrawablesWithIntrinsicBounds(mProviderList.get(position).icon, null,
+                        null, null);
 
                 // Add margin between image and text (support various screen
                 // densities)
@@ -104,13 +101,12 @@ public class OpenPgpListPreference extends DialogPreference {
                 tv.setCompoundDrawablePadding(dp5);
 
                 // disable if it has the wrong api_version
-                if (mProviderList.get(position).apiVersion == REQUIRED_API_VERSION) {
+                if (mProviderList.get(position).apiVersion == OpenPgpConstants.REQUIRED_API_VERSION) {
                     tv.setEnabled(true);
                 } else {
                     tv.setEnabled(false);
-                    tv.setText(tv.getText() + " (API v"
-                            + mProviderList.get(position).apiVersion + ", needs v"
-                            + REQUIRED_API_VERSION + ")");
+                    tv.setText(tv.getText() + " (API v" + mProviderList.get(position).apiVersion
+                            + ", needs v" + OpenPgpConstants.REQUIRED_API_VERSION + ")");
                 }
 
                 return v;
@@ -125,8 +121,8 @@ public class OpenPgpListPreference extends DialogPreference {
                         mSelectedPackage = mProviderList.get(which).packageName;
 
                         /*
-                         * Clicking on an item simulates the positive button
-                         * click, and dismisses the dialog.
+                         * Clicking on an item simulates the positive button click, and dismisses
+                         * the dialog.
                          */
                         OpenPgpListPreference.this.onClick(dialog, DialogInterface.BUTTON_POSITIVE);
                         dialog.dismiss();
@@ -134,9 +130,8 @@ public class OpenPgpListPreference extends DialogPreference {
                 });
 
         /*
-         * The typical interaction for list-based dialogs is to have
-         * click-on-an-item dismiss the dialog instead of the user having to
-         * press 'Ok'.
+         * The typical interaction for list-based dialogs is to have click-on-an-item dismiss the
+         * dialog instead of the user having to press 'Ok'.
          */
         builder.setPositiveButton(null, null);
     }
diff --git a/OpenPGP-Keychain/src/org/openintents/openpgp/OpenPgpServiceConnection.java b/OpenPGP-Keychain/src/org/openintents/openpgp/OpenPgpServiceConnection.java
index 56a922d73..f7ba06aaf 100644
--- a/OpenPGP-Keychain/src/org/openintents/openpgp/OpenPgpServiceConnection.java
+++ b/OpenPGP-Keychain/src/org/openintents/openpgp/OpenPgpServiceConnection.java
@@ -29,14 +29,12 @@ public class OpenPgpServiceConnection {
     private Context mApplicationContext;
 
     private IOpenPgpService mService;
-    private boolean bound;
-    private String cryptoProviderPackageName;
-
-    private static final String TAG = "OpenPgpServiceConnection";
+    private boolean mBound;
+    private String mCryptoProviderPackageName;
 
     public OpenPgpServiceConnection(Context context, String cryptoProviderPackageName) {
-        mApplicationContext = context.getApplicationContext();
-        this.cryptoProviderPackageName = cryptoProviderPackageName;
+        this.mApplicationContext = context.getApplicationContext();
+        this.mCryptoProviderPackageName = cryptoProviderPackageName;
     }
 
     public IOpenPgpService getService() {
@@ -44,20 +42,20 @@ public class OpenPgpServiceConnection {
     }
 
     public boolean isBound() {
-        return bound;
+        return mBound;
     }
 
     private ServiceConnection mCryptoServiceConnection = new ServiceConnection() {
         public void onServiceConnected(ComponentName name, IBinder service) {
             mService = IOpenPgpService.Stub.asInterface(service);
-            Log.d(TAG, "connected to service");
-            bound = true;
+            Log.d(OpenPgpConstants.TAG, "connected to service");
+            mBound = true;
         }
 
         public void onServiceDisconnected(ComponentName name) {
             mService = null;
-            Log.d(TAG, "disconnected from service");
-            bound = false;
+            Log.d(OpenPgpConstants.TAG, "disconnected from service");
+            mBound = false;
         }
     };
 
@@ -67,23 +65,23 @@ public class OpenPgpServiceConnection {
      * @return
      */
     public boolean bindToService() {
-        if (mService == null && !bound) { // if not already connected
+        if (mService == null && !mBound) { // if not already connected
             try {
-                Log.d(TAG, "not bound yet");
+                Log.d(OpenPgpConstants.TAG, "not bound yet");
 
                 Intent serviceIntent = new Intent();
                 serviceIntent.setAction(IOpenPgpService.class.getName());
-                serviceIntent.setPackage(cryptoProviderPackageName);
+                serviceIntent.setPackage(mCryptoProviderPackageName);
                 mApplicationContext.bindService(serviceIntent, mCryptoServiceConnection,
                         Context.BIND_AUTO_CREATE);
 
                 return true;
             } catch (Exception e) {
-                Log.d(TAG, "Exception", e);
+                Log.d(OpenPgpConstants.TAG, "Exception on binding", e);
                 return false;
             }
-        } else { // already connected
-            Log.d(TAG, "already bound... ");
+        } else {
+            Log.d(OpenPgpConstants.TAG, "already bound");
             return true;
         }
     }
diff --git a/OpenPGP-Keychain/src/org/sufficientlysecure/keychain/provider/KeychainContract.java b/OpenPGP-Keychain/src/org/sufficientlysecure/keychain/provider/KeychainContract.java
index ea4ca377c..82bb473f6 100644
--- a/OpenPGP-Keychain/src/org/sufficientlysecure/keychain/provider/KeychainContract.java
+++ b/OpenPGP-Keychain/src/org/sufficientlysecure/keychain/provider/KeychainContract.java
@@ -55,6 +55,7 @@ public class KeychainContract {
 
     interface ApiAppsColumns {
         String PACKAGE_NAME = "package_name";
+        String PACKAGE_SIGNATURE = "package_signature";
         String KEY_ID = "key_id"; // not a database id
         String ENCRYPTION_ALGORITHM = "encryption_algorithm";
         String HASH_ALORITHM = "hash_algorithm";
diff --git a/OpenPGP-Keychain/src/org/sufficientlysecure/keychain/provider/KeychainDatabase.java b/OpenPGP-Keychain/src/org/sufficientlysecure/keychain/provider/KeychainDatabase.java
index 0f962967d..60c5c91a8 100644
--- a/OpenPGP-Keychain/src/org/sufficientlysecure/keychain/provider/KeychainDatabase.java
+++ b/OpenPGP-Keychain/src/org/sufficientlysecure/keychain/provider/KeychainDatabase.java
@@ -31,7 +31,7 @@ import android.provider.BaseColumns;
 
 public class KeychainDatabase extends SQLiteOpenHelper {
     private static final String DATABASE_NAME = "apg.db";
-    private static final int DATABASE_VERSION = 5;
+    private static final int DATABASE_VERSION = 6;
 
     public interface Tables {
         String KEY_RINGS = "key_rings";
@@ -66,9 +66,10 @@ public class KeychainDatabase extends SQLiteOpenHelper {
 
     private static final String CREATE_API_APPS = "CREATE TABLE IF NOT EXISTS " + Tables.API_APPS
             + " (" + BaseColumns._ID + " INTEGER PRIMARY KEY AUTOINCREMENT, "
-            + ApiAppsColumns.PACKAGE_NAME + " TEXT UNIQUE, " + ApiAppsColumns.KEY_ID + " INT64, "
-            + ApiAppsColumns.ENCRYPTION_ALGORITHM + " INTEGER, " + ApiAppsColumns.HASH_ALORITHM
-            + " INTEGER, " + ApiAppsColumns.COMPRESSION + " INTEGER)";
+            + ApiAppsColumns.PACKAGE_NAME + " TEXT UNIQUE, " + ApiAppsColumns.PACKAGE_SIGNATURE
+            + " BLOB, " + ApiAppsColumns.KEY_ID + " INT64, " + ApiAppsColumns.ENCRYPTION_ALGORITHM
+            + " INTEGER, " + ApiAppsColumns.HASH_ALORITHM + " INTEGER, "
+            + ApiAppsColumns.COMPRESSION + " INTEGER)";
 
     KeychainDatabase(Context context) {
         super(context, DATABASE_NAME, null, DATABASE_VERSION);
@@ -110,6 +111,10 @@ public class KeychainDatabase extends SQLiteOpenHelper {
                 break;
             case 4:
                 db.execSQL(CREATE_API_APPS);
+            case 5:
+                // new column: package_signature
+                db.execSQL("DROP TABLE IF EXISTS " + Tables.API_APPS);
+                db.execSQL(CREATE_API_APPS);
 
             default:
                 break;
diff --git a/OpenPGP-Keychain/src/org/sufficientlysecure/keychain/provider/ProviderHelper.java b/OpenPGP-Keychain/src/org/sufficientlysecure/keychain/provider/ProviderHelper.java
index 7ef61c15b..f12048277 100644
--- a/OpenPGP-Keychain/src/org/sufficientlysecure/keychain/provider/ProviderHelper.java
+++ b/OpenPGP-Keychain/src/org/sufficientlysecure/keychain/provider/ProviderHelper.java
@@ -742,6 +742,7 @@ public class ProviderHelper {
     private static ContentValues contentValueForApiApps(AppSettings appSettings) {
         ContentValues values = new ContentValues();
         values.put(ApiApps.PACKAGE_NAME, appSettings.getPackageName());
+        values.put(ApiApps.PACKAGE_SIGNATURE, appSettings.getPackageSignature());
         values.put(ApiApps.KEY_ID, appSettings.getKeyId());
         values.put(ApiApps.COMPRESSION, appSettings.getCompression());
         values.put(ApiApps.ENCRYPTION_ALGORITHM, appSettings.getEncryptionAlgorithm());
@@ -770,6 +771,8 @@ public class ProviderHelper {
             settings = new AppSettings();
             settings.setPackageName(cur.getString(cur
                     .getColumnIndex(KeychainContract.ApiApps.PACKAGE_NAME)));
+            settings.setPackageSignature(cur.getBlob(cur
+                    .getColumnIndex(KeychainContract.ApiApps.PACKAGE_SIGNATURE)));
             settings.setKeyId(cur.getLong(cur.getColumnIndex(KeychainContract.ApiApps.KEY_ID)));
             settings.setCompression(cur.getInt(cur
                     .getColumnIndexOrThrow(KeychainContract.ApiApps.COMPRESSION)));
@@ -781,4 +784,26 @@ public class ProviderHelper {
 
         return settings;
     }
+
+    public static byte[] getApiAppSignature(Context context, String packageName) {
+        Uri queryUri = KeychainContract.ApiApps.buildByPackageNameUri(packageName);
+
+        String[] projection = new String[] { ApiApps.PACKAGE_SIGNATURE };
+
+        ContentResolver cr = context.getContentResolver();
+        Cursor cursor = cr.query(queryUri, projection, null, null, null);
+
+        byte[] signature = null;
+        if (cursor != null && cursor.moveToFirst()) {
+            int signatureCol = 0;
+
+            signature = cursor.getBlob(signatureCol);
+        }
+
+        if (cursor != null) {
+            cursor.close();
+        }
+
+        return signature;
+    }
 }
diff --git a/OpenPGP-Keychain/src/org/sufficientlysecure/keychain/service/exception/WrongPackageSignatureException.java b/OpenPGP-Keychain/src/org/sufficientlysecure/keychain/service/exception/WrongPackageSignatureException.java
new file mode 100644
index 000000000..cef002265
--- /dev/null
+++ b/OpenPGP-Keychain/src/org/sufficientlysecure/keychain/service/exception/WrongPackageSignatureException.java
@@ -0,0 +1,10 @@
+package org.sufficientlysecure.keychain.service.exception;
+
+public class WrongPackageSignatureException extends Exception {
+
+    private static final long serialVersionUID = -8294642703122196028L;
+
+    public WrongPackageSignatureException(String message) {
+        super(message);
+    }
+}
\ No newline at end of file
diff --git a/OpenPGP-Keychain/src/org/sufficientlysecure/keychain/service/remote/AppSettings.java b/OpenPGP-Keychain/src/org/sufficientlysecure/keychain/service/remote/AppSettings.java
index 381a4065c..9da4c8392 100644
--- a/OpenPGP-Keychain/src/org/sufficientlysecure/keychain/service/remote/AppSettings.java
+++ b/OpenPGP-Keychain/src/org/sufficientlysecure/keychain/service/remote/AppSettings.java
@@ -23,6 +23,7 @@ import org.sufficientlysecure.keychain.Id;
 
 public class AppSettings {
     private String packageName;
+    private byte[] packageSignature;
     private long keyId = Id.key.none;
     private int encryptionAlgorithm;
     private int hashAlgorithm;
@@ -32,9 +33,10 @@ public class AppSettings {
 
     }
 
-    public AppSettings(String packageName) {
+    public AppSettings(String packageName, byte[] packageSignature) {
         super();
         this.packageName = packageName;
+        this.packageSignature = packageSignature;
         // defaults:
         this.encryptionAlgorithm = PGPEncryptedData.AES_256;
         this.hashAlgorithm = HashAlgorithmTags.SHA512;
@@ -49,6 +51,14 @@ public class AppSettings {
         this.packageName = packageName;
     }
 
+    public byte[] getPackageSignature() {
+        return packageSignature;
+    }
+
+    public void setPackageSignature(byte[] packageSignature) {
+        this.packageSignature = packageSignature;
+    }
+
     public long getKeyId() {
         return keyId;
     }
diff --git a/OpenPGP-Keychain/src/org/sufficientlysecure/keychain/service/remote/AppSettingsFragment.java b/OpenPGP-Keychain/src/org/sufficientlysecure/keychain/service/remote/AppSettingsFragment.java
index 942f8eba8..e592f5d57 100644
--- a/OpenPGP-Keychain/src/org/sufficientlysecure/keychain/service/remote/AppSettingsFragment.java
+++ b/OpenPGP-Keychain/src/org/sufficientlysecure/keychain/service/remote/AppSettingsFragment.java
@@ -17,8 +17,12 @@
 
 package org.sufficientlysecure.keychain.service.remote;
 
+import java.security.MessageDigest;
+import java.security.NoSuchAlgorithmException;
+
 import org.spongycastle.openpgp.PGPSecretKey;
 import org.spongycastle.openpgp.PGPSecretKeyRing;
+import org.spongycastle.util.encoders.Hex;
 import org.sufficientlysecure.keychain.Constants;
 import org.sufficientlysecure.keychain.Id;
 import org.sufficientlysecure.keychain.R;
@@ -67,6 +71,8 @@ public class AppSettingsFragment extends Fragment {
     private Spinner mEncryptionAlgorithm;
     private Spinner mHashAlgorithm;
     private Spinner mCompression;
+    private TextView mPackageName;
+    private TextView mPackageSignature;
 
     KeyValueSpinnerAdapter encryptionAdapter;
     KeyValueSpinnerAdapter hashAdapter;
@@ -79,6 +85,19 @@ public class AppSettingsFragment extends Fragment {
     public void setAppSettings(AppSettings appSettings) {
         this.appSettings = appSettings;
         setPackage(appSettings.getPackageName());
+        mPackageName.setText(appSettings.getPackageName());
+
+        try {
+            MessageDigest md = MessageDigest.getInstance("SHA-256");
+            md.update(appSettings.getPackageSignature());
+            byte[] digest = md.digest();
+            String signature = new String(Hex.encode(digest));
+
+            mPackageSignature.setText(signature);
+        } catch (NoSuchAlgorithmException e) {
+            Log.e(Constants.TAG, "Should not happen!", e);
+        }
+
         updateSelectedKeyView(appSettings.getKeyId());
         mEncryptionAlgorithm.setSelection(encryptionAdapter.getPosition(appSettings
                 .getEncryptionAlgorithm()));
@@ -110,6 +129,8 @@ public class AppSettingsFragment extends Fragment {
                 .findViewById(R.id.api_app_settings_encryption_algorithm);
         mHashAlgorithm = (Spinner) view.findViewById(R.id.api_app_settings_hash_algorithm);
         mCompression = (Spinner) view.findViewById(R.id.api_app_settings_compression);
+        mPackageName = (TextView) view.findViewById(R.id.api_app_settings_package_name);
+        mPackageSignature = (TextView) view.findViewById(R.id.api_app_settings_package_signature);
 
         AlgorithmNames algorithmNames = new AlgorithmNames(getActivity());
 
@@ -182,7 +203,7 @@ public class AppSettingsFragment extends Fragment {
             public void onClick(View v) {
                 if (mAdvancedSettingsContainer.getVisibility() == View.VISIBLE) {
                     mAdvancedSettingsContainer.startAnimation(invisibleAnimation);
-                    mAdvancedSettingsContainer.setVisibility(View.INVISIBLE);
+                    mAdvancedSettingsContainer.setVisibility(View.GONE);
                     mAdvancedSettingsButton.setText(R.string.api_settings_show_advanced);
                 } else {
                     mAdvancedSettingsContainer.startAnimation(visibleAnimation);
diff --git a/OpenPGP-Keychain/src/org/sufficientlysecure/keychain/service/remote/RemoteService.java b/OpenPGP-Keychain/src/org/sufficientlysecure/keychain/service/remote/RemoteService.java
index 4e8c4678a..0f28d96f6 100644
--- a/OpenPGP-Keychain/src/org/sufficientlysecure/keychain/service/remote/RemoteService.java
+++ b/OpenPGP-Keychain/src/org/sufficientlysecure/keychain/service/remote/RemoteService.java
@@ -18,18 +18,24 @@
 package org.sufficientlysecure.keychain.service.remote;
 
 import java.util.ArrayList;
+import java.util.Arrays;
 import java.util.concurrent.ArrayBlockingQueue;
 import java.util.concurrent.TimeUnit;
 
 import org.sufficientlysecure.keychain.Constants;
 import org.sufficientlysecure.keychain.provider.KeychainContract;
 import org.sufficientlysecure.keychain.provider.ProviderHelper;
+import org.sufficientlysecure.keychain.service.exception.WrongPackageSignatureException;
 import org.sufficientlysecure.keychain.util.Log;
 import org.sufficientlysecure.keychain.util.PausableThreadPoolExecutor;
 
 import android.app.Service;
 import android.content.Context;
 import android.content.Intent;
+import android.content.pm.PackageInfo;
+import android.content.pm.PackageManager;
+import android.content.pm.PackageManager.NameNotFoundException;
+import android.content.pm.Signature;
 import android.net.Uri;
 import android.os.Binder;
 import android.os.Bundle;
@@ -38,7 +44,7 @@ import android.os.Message;
 import android.os.Messenger;
 
 /**
- * Abstract service for remote APIs that handle app registration and user input.
+ * Abstract service class for remote APIs that handle app registration and user input.
  */
 public abstract class RemoteService extends Service {
     Context mContext;
@@ -98,32 +104,57 @@ public abstract class RemoteService extends Service {
      * @param r
      */
     protected void checkAndEnqueue(Runnable r) {
-        if (isCallerAllowed(false)) {
-            mThreadPool.execute(r);
-
-            Log.d(Constants.TAG, "Enqueued runnable…");
-        } else {
-            String[] callingPackages = getPackageManager()
-                    .getPackagesForUid(Binder.getCallingUid());
-
-            Log.e(Constants.TAG, "Not allowed to use service! Starting activity for registration!");
-            Bundle extras = new Bundle();
-            // TODO: currently simply uses first entry
-            extras.putString(RemoteServiceActivity.EXTRA_PACKAGE_NAME, callingPackages[0]);
-
-            RegisterActivityCallback callback = new RegisterActivityCallback();
-
-            pauseAndStartUserInteraction(RemoteServiceActivity.ACTION_REGISTER, callback, extras);
-
-            if (callback.isAllowed()) {
+        try {
+            if (isCallerAllowed(false)) {
                 mThreadPool.execute(r);
+
                 Log.d(Constants.TAG, "Enqueued runnable…");
             } else {
-                Log.d(Constants.TAG, "User disallowed app!");
+                String[] callingPackages = getPackageManager().getPackagesForUid(
+                        Binder.getCallingUid());
+                // TODO: currently simply uses first entry
+                String packageName = callingPackages[0];
+
+                byte[] packageSignature;
+                try {
+                    packageSignature = getPackageSignature(packageName);
+                } catch (NameNotFoundException e) {
+                    Log.e(Constants.TAG, "Should not happen, returning!", e);
+                    return;
+                }
+                Log.e(Constants.TAG,
+                        "Not allowed to use service! Starting activity for registration!");
+                Bundle extras = new Bundle();
+                extras.putString(RemoteServiceActivity.EXTRA_PACKAGE_NAME, packageName);
+                extras.putByteArray(RemoteServiceActivity.EXTRA_PACKAGE_SIGNATURE, packageSignature);
+                RegisterActivityCallback callback = new RegisterActivityCallback();
+
+                pauseAndStartUserInteraction(RemoteServiceActivity.ACTION_REGISTER, callback,
+                        extras);
+
+                if (callback.isAllowed()) {
+                    mThreadPool.execute(r);
+                    Log.d(Constants.TAG, "Enqueued runnable…");
+                } else {
+                    Log.d(Constants.TAG, "User disallowed app!");
+                }
             }
+        } catch (WrongPackageSignatureException e) {
+            // TODO: Inform user about wrong signature!
+            Log.e(Constants.TAG, "RemoteService", e);
         }
     }
 
+    private byte[] getPackageSignature(String packageName) throws NameNotFoundException {
+        PackageInfo pkgInfo = getPackageManager().getPackageInfo(packageName,
+                PackageManager.GET_SIGNATURES);
+        Signature[] signatures = pkgInfo.signatures;
+        // TODO: Only first signature?!
+        byte[] packageSignature = signatures[0].toByteArray();
+
+        return packageSignature;
+    }
+
     /**
      * Locks current thread and pauses execution of runnables and starts activity for user input
      * 
@@ -200,15 +231,20 @@ public abstract class RemoteService extends Service {
                 packageName = msg.getData().getString(PACKAGE_NAME);
 
                 // resume threads
-                if (isPackageAllowed(packageName, false)) {
-                    synchronized (userInputLock) {
-                        userInputLock.notifyAll();
+                try {
+                    if (isPackageAllowed(packageName)) {
+                        synchronized (userInputLock) {
+                            userInputLock.notifyAll();
+                        }
+                        mThreadPool.resume();
+                    } else {
+                        // Should not happen!
+                        Log.e(Constants.TAG, "Should not happen! Emergency shutdown!");
+                        mThreadPool.shutdownNow();
                     }
-                    mThreadPool.resume();
-                } else {
-                    // Should not happen!
-                    Log.e(Constants.TAG, "Should not happen! Emergency shutdown!");
-                    mThreadPool.shutdownNow();
+                } catch (WrongPackageSignatureException e) {
+                    // TODO: Inform user about wrong signature!
+                    Log.e(Constants.TAG, "RemoteService", e);
                 }
             } else {
                 allowed = false;
@@ -230,15 +266,28 @@ public abstract class RemoteService extends Service {
      * @param allowOnlySelf
      *            allow only Keychain app itself
      * @return true if process is allowed to use this service
+     * @throws WrongPackageSignatureException
      */
-    private boolean isCallerAllowed(boolean allowOnlySelf) {
-        String[] callingPackages = getPackageManager().getPackagesForUid(Binder.getCallingUid());
+    private boolean isCallerAllowed(boolean allowOnlySelf) throws WrongPackageSignatureException {
+        return isUidAllowed(Binder.getCallingUid(), allowOnlySelf);
+    }
+
+    private boolean isUidAllowed(int uid, boolean allowOnlySelf)
+            throws WrongPackageSignatureException {
+        if (android.os.Process.myUid() == uid) {
+            return true;
+        }
+        if (allowOnlySelf) { // barrier
+            return false;
+        }
+
+        String[] callingPackages = getPackageManager().getPackagesForUid(uid);
 
         // is calling package allowed to use this service?
         for (int i = 0; i < callingPackages.length; i++) {
             String currentPkg = callingPackages[i];
 
-            if (isPackageAllowed(currentPkg, allowOnlySelf)) {
+            if (isPackageAllowed(currentPkg)) {
                 return true;
             }
         }
@@ -248,28 +297,39 @@ public abstract class RemoteService extends Service {
     }
 
     /**
-     * Checks if packageName is a registered app for the API.
+     * Checks if packageName is a registered app for the API. Does not return true for own package!
      * 
      * @param packageName
-     * @param allowOnlySelf
-     *            allow only Keychain app itself
      * @return
+     * @throws WrongPackageSignatureException
      */
-    private boolean isPackageAllowed(String packageName, boolean allowOnlySelf) {
+    private boolean isPackageAllowed(String packageName) throws WrongPackageSignatureException {
         Log.d(Constants.TAG, "packageName: " + packageName);
 
-        ArrayList<String> allowedPkgs = ProviderHelper.getRegisteredApiApps(mContext);
+        ArrayList<String> allowedPkgs = ProviderHelper.getRegisteredApiApps(this);
         Log.d(Constants.TAG, "allowed: " + allowedPkgs);
 
         // check if package is allowed to use our service
-        if (allowedPkgs.contains(packageName) && (!allowOnlySelf)) {
+        if (allowedPkgs.contains(packageName)) {
             Log.d(Constants.TAG, "Package is allowed! packageName: " + packageName);
 
-            return true;
-        } else if (Constants.PACKAGE_NAME.equals(packageName)) {
-            Log.d(Constants.TAG, "Package is OpenPGP Keychain! -> allowed!");
+            // check package signature
+            byte[] currentSig;
+            try {
+                currentSig = getPackageSignature(packageName);
+            } catch (NameNotFoundException e) {
+                throw new WrongPackageSignatureException(e.getMessage());
+            }
 
-            return true;
+            byte[] storedSig = ProviderHelper.getApiAppSignature(this, packageName);
+            if (Arrays.equals(currentSig, storedSig)) {
+                Log.d(Constants.TAG,
+                        "Package signature is correct! (equals signature from database)");
+                return true;
+            } else {
+                throw new WrongPackageSignatureException(
+                        "PACKAGE NOT ALLOWED! Signature wrong! (Signature not equals signature from database)");
+            }
         }
 
         return false;
diff --git a/OpenPGP-Keychain/src/org/sufficientlysecure/keychain/service/remote/RemoteServiceActivity.java b/OpenPGP-Keychain/src/org/sufficientlysecure/keychain/service/remote/RemoteServiceActivity.java
index 2c4bb4e97..bba8176b1 100644
--- a/OpenPGP-Keychain/src/org/sufficientlysecure/keychain/service/remote/RemoteServiceActivity.java
+++ b/OpenPGP-Keychain/src/org/sufficientlysecure/keychain/service/remote/RemoteServiceActivity.java
@@ -55,6 +55,7 @@ public class RemoteServiceActivity extends SherlockFragmentActivity {
     public static final String EXTRA_SECRET_KEY_ID = "secret_key_id";
     // register action
     public static final String EXTRA_PACKAGE_NAME = "package_name";
+    public static final String EXTRA_PACKAGE_SIGNATURE = "package_signature";
     // select pub keys action
     public static final String EXTRA_SELECTED_MASTER_KEY_IDS = "master_key_ids";
     public static final String EXTRA_MISSING_USER_IDS = "missing_user_ids";
@@ -110,6 +111,7 @@ public class RemoteServiceActivity extends SherlockFragmentActivity {
          */
         if (ACTION_REGISTER.equals(action)) {
             final String packageName = extras.getString(EXTRA_PACKAGE_NAME);
+            final byte[] packageSignature = extras.getByteArray(EXTRA_PACKAGE_SIGNATURE);
 
             // Inflate a "Done"/"Cancel" custom action bar view
             ActionBarHelper.setDoneCancelView(getSupportActionBar(), R.string.api_register_allow,
@@ -166,7 +168,7 @@ public class RemoteServiceActivity extends SherlockFragmentActivity {
             mSettingsFragment = (AppSettingsFragment) getSupportFragmentManager().findFragmentById(
                     R.id.api_app_settings_fragment);
 
-            AppSettings settings = new AppSettings(packageName);
+            AppSettings settings = new AppSettings(packageName, packageSignature);
             mSettingsFragment.setAppSettings(settings);
         } else if (ACTION_CACHE_PASSPHRASE.equals(action)) {
             long secretKeyId = extras.getLong(EXTRA_SECRET_KEY_ID);