1.01 pre1:

added preferences to switch encryption+kdf and to edit kdf parameters (for AES and Argon2)

src/KeePassLib2Android/Cryptography/Cipher/CipherPool.cs

@@ -46,7 +46,6 @@ namespace KeePassLib.Cryptography.Cipher
 					cp = new CipherPool();
 					cp.AddCipher(new StandardAesEngine());
 					cp.AddCipher(new ChaCha20Engine());
-
 					m_poolGlobal = cp;
 				}
 
@@ -161,5 +160,12 @@ namespace KeePassLib.Cryptography.Cipher
 				return m_vCiphers[nIndex];
 			}
 		}
+
+		public IEnumerable<ICipherEngine> Engines
+		{
+			get {
+				return m_vCiphers;
+			}
+		}
 	}
 }

src/KeePassLib2Android/Cryptography/KeyDerivation/AesKdf.cs

@@ -122,6 +122,7 @@ namespace KeePassLib.Cryptography.KeyDerivation
 				// Try to use the native library first
 				if (NativeLib.TransformKey256(pbNewKey, pbKeySeed32, uNumRounds))
 				{
+					//no need to hash, this is already done in the native library.
 					byte[] pbKey = new byte[32];
 					Array.Copy(pbNewKey, pbKey, pbNewKey.Length);
 

src/keepass2android/ChangeLog.cs

@@ -26,6 +26,7 @@ namespace keepass2android
 			AlertDialog.Builder builder = new AlertDialog.Builder(new ContextThemeWrapper(ctx, Android.Resource.Style.ThemeHoloLightDialog));
 			builder.SetTitle(ctx.GetString(Resource.String.ChangeLog_title));
 			List<string> changeLog = new List<string>{
+				ctx.GetString(Resource.String.ChangeLog_1_01_preview),
 				ctx.GetString(Resource.String.ChangeLog_1_0_0e),
 				ctx.GetString(Resource.String.ChangeLog_1_0_0),
 				ctx.GetString(Resource.String.ChangeLog_0_9_9c),				

src/keepass2android/Properties/AndroidManifest_net.xml

@@ -1,7 +1,7 @@
 <?xml version="1.0" encoding="utf-8"?>
 <manifest xmlns:android="http://schemas.android.com/apk/res/android" 
-			android:versionCode="81" 
-			android:versionName="1.0.0-e" 
+			android:versionCode="82" 
+			android:versionName="1.01-pre1" 
 			package="keepass2android.keepass2android" 
 			android:installLocation="auto">
 	<uses-sdk android:minSdkVersion="14" android:targetSdkVersion="23" />

src/keepass2android/Resources/layout/database_settings.xml

@@ -26,7 +26,6 @@
 	  android:layout_width="fill_parent"
 	  android:inputType="number"/> 
 	<TextView android:id="@+id/rounds_explaination" 
-	  android:text="@string/rounds_explaination"
 	  android:layout_height="wrap_content"
 	  android:layout_width="wrap_content" 
 	  android:layout_below="@id/rounds"/>

src/keepass2android/Resources/values/config.xml

@@ -52,8 +52,10 @@
     <string name="app_timeout_key">app_timeout_key</string>
 	<string name="show_kill_app_key">show_kill_app_key</string>
     <string name="clipboard_timeout_key">clip_timeout_key</string>
-    <string name="db_key">db</string>
-    <string name="rounds_key">rounds</string>
+  <string name="db_key">db</string>
+  <string name="kdf_screen_key">kdf_screen</string>
+  <string name="kdf_key">kdf_key</string>
+  <string name="rounds_key">rounds</string>
 	<string name="master_pwd_key">change_master_pwd</string>
     <string name="keyfile_key">keyfile</string>
     <string name="maskpass_key">maskpass</string>

src/keepass2android/Resources/values/strings.xml

@@ -64,6 +64,9 @@
 	<string name="brackets">Brackets</string>
   <string name="cancel">Cancel</string>
   <string name="ClearClipboard">Clipboard cleared.</string>
+  
+  
+  
   <string name="clipboard_timeout">Clipboard timeout</string>
   <string name="clipboard_timeout_summary">Time before clearing clipboard after copying username or password</string>
   <string name="copy_username">Select to copy username to clipboard</string>
@@ -138,6 +141,8 @@
   <string name="error_pass_gen_type">At least one password generation type must be selected</string>
   <string name="error_pass_match">Passwords do not match.</string>
   <string name="error_rounds_not_number">Rounds must be a number.</string>
+  <string name="error_param_not_number">Parameter must be a number.</string>
+  
   <string name="error_title_required">A title is required.</string>
   <string name="error_wrong_length">Enter a positive integer on length field</string>
   <string name="FileNotFound">File not found.</string>
@@ -216,9 +221,17 @@
   <string name="remove_from_filelist">Remove</string>
   <string name="rijndael">Rijndael (AES)</string>
   <string name="root">Root</string>
+
+  <string name="KeyDerivFunc">Key derivation function</string>
+  
   <string name="rounds">Encryption Rounds</string>
   <string name="rounds_explaination">Higher encryption rounds provide additional protection against brute force attacks, but can really slow down loading and saving.</string>
   <string name="rounds_hint">rounds</string>
+
+
+  <string name="argon2memory">Memory for Argon 2 (bytes)</string>
+  <string name="argon2parallelism">Parallelism for Argon 2</string>
+
   <string name="database_name">Database name</string>
   <string name="default_username">Default user name for new entries</string>
   <string name="saving_database">Saving database…</string>
@@ -662,6 +675,12 @@
     * Bug fix: Previous release contained two input methods (one crashing)\n
   </string>
 
+  <string name="ChangeLog_1_01_preview">
+    Version 1.01-pre1\n
+    * NOTE: this is a preview, ONLY use for testing!\n
+    * added preview-support for the new KDBX-4-format (see http://keepass.info/help/kb/kdbx_4.html) including Argon2 key derivation and ChaCha20 encryption. Argon2 is currently only implemented in managed code. Expect a slow transformation process.\n
+  </string>
+
   <string name="ChangeLog_1_0_0e">
     Version 1.0.0e\n
     * fix for Fingerprint Unlock on older Samsung devices with Android 6\n

src/keepass2android/Resources/xml/preferences.xml

@@ -31,18 +31,59 @@
                 android:title="@string/database_name"
                 android:persistent="false"
                 android:key="@string/database_name_key"/>
-		<Preference
-		  android:key="@string/algorithm_key"
-		  android:title="@string/algorithm"
-		  android:enabled="false"/>
-		<keepass2android.settings.RoundsPreference
+		
+      <ListPreference
+			  android:key="@string/algorithm_key"
+			  android:title="@string/algorithm"
+			  android:dialogTitle="@string/algorithm"/>
+
+    <PreferenceScreen
+	  android:key="@string/kdf_screen_key"
+	  android:title="@string/KeyDerivFunc" >
+<keepass2android.ToolbarPreference
+    android:key="@string/kdf_screen_key"
+    android:title="@string/KeyDerivFunc" />
+     
+      <ListPreference
+			  android:key="@string/kdf_key"
+			  android:title="@string/KeyDerivFunc"
+			  android:dialogTitle="@string/KeyDerivFunc"/>
+
+      
+
+    <keepass2android.settings.RoundsPreference
 		  android:key="@string/rounds_key"
 		  android:persistent="false"
 		  android:title="@string/rounds"
 		  android:dialogLayout="@layout/database_settings"
 		  android:positiveButtonText="@string/entry_save"
 		  android:negativeButtonText="@string/entry_cancel"/>
-
+    
+    <keepass2android.settings.Argon2RoundsPreference
+		  android:key="argon2rounds"
+		  android:persistent="false"
+		  android:title="@string/rounds"
+		  android:dialogLayout="@layout/database_settings"
+		  android:positiveButtonText="@string/entry_save"
+		  android:negativeButtonText="@string/entry_cancel"/>
+    
+    <keepass2android.settings.Argon2MemoryPreference
+		  android:key="argon2memory"
+		  android:persistent="false"
+		  android:title="@string/argon2memory"
+		  android:dialogLayout="@layout/database_settings"
+		  android:positiveButtonText="@string/entry_save"
+		  android:negativeButtonText="@string/entry_cancel"/>
+    
+    <keepass2android.settings.Argon2ParallelismPreference
+		  android:key="argon2parallelism"
+		  android:persistent="false"
+		  android:title="@string/argon2parallelism"
+		  android:dialogLayout="@layout/database_settings"
+		  android:positiveButtonText="@string/entry_save"
+		  android:negativeButtonText="@string/entry_cancel"/>
+</PreferenceScreen>
+  
 		<EditTextPreference
 			  android:title="@string/default_username"
 			  android:persistent="false"
@@ -84,6 +125,7 @@
 		
     
 	</PreferenceScreen>
+	
 
 	<PreferenceScreen
 	  android:key="@string/app_key"

src/keepass2android/keepass2android.csproj

@@ -26,7 +26,7 @@
     <DebugType>full</DebugType>
     <Optimize>false</Optimize>
     <OutputPath>bin\Debug</OutputPath>
-    <DefineConstants>DEBUG;EXCLUDE_TWOFISH;_EXCLUDE_KEYBOARD;_EXCLUDE_FILECHOOSER;_EXCLUDE_JAVAFILESTORAGE;INCLUDE_KEYTRANSFORM</DefineConstants>
+    <DefineConstants>DEBUG;_EXCLUDE_TWOFISH;_EXCLUDE_KEYBOARD;_EXCLUDE_FILECHOOSER;_EXCLUDE_JAVAFILESTORAGE;INCLUDE_KEYTRANSFORM</DefineConstants>
     <ErrorReport>prompt</ErrorReport>
     <WarningLevel>4</WarningLevel>
     <ConsolePause>False</ConsolePause>
@@ -182,6 +182,7 @@
     <Compile Include="search\SearchProvider.cs" />
     <Compile Include="SelectStorageLocationActivity.cs" />
     <Compile Include="services\OngoingNotificationsService.cs" />
+    <Compile Include="settings\Argon2Preference.cs" />
     <Compile Include="settings\DatabaseSettingsActivity.cs" />
     <Compile Include="intents\Intents.cs" />
     <Compile Include="timeout\TimeoutHelper.cs" />
@@ -590,7 +591,9 @@
     <AndroidResource Include="Resources\layout\about.xml">
       <SubType>Designer</SubType>
     </AndroidResource>
-    <AndroidResource Include="Resources\layout\database_settings.xml" />
+    <AndroidResource Include="Resources\layout\database_settings.xml">
+      <SubType>Designer</SubType>
+    </AndroidResource>
     <AndroidResource Include="Resources\layout\entry_edit.xml">
       <SubType>Designer</SubType>
     </AndroidResource>

src/keepass2android/settings/Argon2Preference.cs

@@ -0,0 +1,101 @@
+using Android.Content;
+using Android.Util;
+using KeePassLib.Cryptography.KeyDerivation;
+
+namespace keepass2android.settings
+{
+	public class Argon2RoundsPreference: KdfNumberParamPreference
+	{
+		public Argon2RoundsPreference(Context context, IAttributeSet attrs) : base(context, attrs)
+		{
+		}
+
+		public Argon2RoundsPreference(Context context, IAttributeSet attrs, int defStyle) : base(context, attrs, defStyle)
+		{
+		}
+
+		public override ulong ParamValue
+		{
+			get
+			{
+				var kdfparams = App.Kp2a.GetDb().KpDatabase.KdfParameters;
+				var kdf = KdfPool.Get(App.Kp2a.GetDb().KpDatabase.KdfParameters.KdfUuid);
+				if (!(kdf is Argon2Kdf))
+				{
+					new Argon2Kdf().GetDefaultParameters();
+				}
+				
+				return kdfparams.GetUInt64(Argon2Kdf.ParamIterations, 0);
+			}
+			set
+			{
+				App.Kp2a.GetDb().KpDatabase.KdfParameters.SetUInt64(Argon2Kdf.ParamIterations, value);
+			}
+		}
+	}
+
+	public class Argon2ParallelismPreference : KdfNumberParamPreference
+	{
+		public Argon2ParallelismPreference(Context context, IAttributeSet attrs)
+			: base(context, attrs)
+		{
+		}
+
+		public Argon2ParallelismPreference(Context context, IAttributeSet attrs, int defStyle)
+			: base(context, attrs, defStyle)
+		{
+		}
+
+		public override ulong ParamValue
+		{
+			get
+			{
+				var kdfparams = App.Kp2a.GetDb().KpDatabase.KdfParameters;
+				var kdf = KdfPool.Get(App.Kp2a.GetDb().KpDatabase.KdfParameters.KdfUuid);
+				if (!(kdf is Argon2Kdf))
+				{
+					new Argon2Kdf().GetDefaultParameters();
+				}
+
+				return kdfparams.GetUInt32(Argon2Kdf.ParamParallelism, 0);
+			}
+			set
+			{
+				App.Kp2a.GetDb().KpDatabase.KdfParameters.SetUInt32(Argon2Kdf.ParamParallelism, (uint) value);
+			}
+		}
+	}
+
+	public class Argon2MemoryPreference : KdfNumberParamPreference
+	{
+		public Argon2MemoryPreference(Context context, IAttributeSet attrs)
+			: base(context, attrs)
+		{
+		}
+
+		public Argon2MemoryPreference(Context context, IAttributeSet attrs, int defStyle)
+			: base(context, attrs, defStyle)
+		{
+		}
+
+		public override ulong ParamValue
+		{
+			get
+			{
+				var kdfparams = App.Kp2a.GetDb().KpDatabase.KdfParameters;
+				var kdf = KdfPool.Get(App.Kp2a.GetDb().KpDatabase.KdfParameters.KdfUuid);
+				if (!(kdf is Argon2Kdf))
+				{
+					new Argon2Kdf().GetDefaultParameters();
+				}
+
+				return kdfparams.GetUInt64(Argon2Kdf.ParamMemory, 0);
+			}
+			set
+			{
+				App.Kp2a.GetDb().KpDatabase.KdfParameters.SetUInt64(Argon2Kdf.ParamMemory, value);
+			}
+		}
+	}
+
+}

src/keepass2android/settings/DatabaseSettingsActivity.cs

@@ -39,6 +39,8 @@ using KeePassLib.Serialization;
 using KeePassLib.Utility;
 using keepass2android.Io;
 using keepass2android.Utils;
+using KeePassLib;
+using KeePassLib.Cryptography.KeyDerivation;
 
 namespace keepass2android
 {
@@ -313,8 +315,9 @@ namespace keepass2android
         }
 
         private KeyboardSwitchPrefManager _switchPrefManager;
+		private Preference aesRounds, argon2parallelism, argon2rounds, argon2memory;
 
-        void OnRememberKeyFileHistoryChanged(object sender, Preference.PreferenceChangeEventArgs eventArgs)
+	    void OnRememberKeyFileHistoryChanged(object sender, Preference.PreferenceChangeEventArgs eventArgs)
         {
             if (!(bool)eventArgs.NewValue)
             {
@@ -344,19 +347,38 @@ namespace keepass2android
             Database db = App.Kp2a.GetDb();
             if (db.Loaded)
             {
-                /*Preference rounds = FindPreference(GetString(Resource.String.rounds_key));
-                rounds.PreferenceChange += (sender, e) => SetRounds(db, e.Preference);
-                rounds.Enabled = db.CanWrite;
-                SetRounds(db, rounds);
-				*/
+	            ListPreference kdfPref = (ListPreference) FindPreference(GetString(Resource.String.kdf_key));
+	            kdfPref.SetEntries(KdfPool.Engines.Select(eng => eng.Name).ToArray());
+	            string[] kdfValues = KdfPool.Engines.Select(eng => eng.Uuid.ToHexString()).ToArray();
+				kdfPref.SetEntryValues(kdfValues);
+				kdfPref.SetValueIndex(kdfValues.Select((v, i) => new {kdf = v, index = i}).First(el => el.kdf == db.KpDatabase.KdfParameters.KdfUuid.ToHexString()).index);
+				kdfPref.PreferenceChange += OnKdfChange;
+				
+				aesRounds = FindPreference(GetString(Resource.String.rounds_key));
+				argon2rounds = FindPreference("argon2rounds");
+				argon2memory = FindPreference("argon2memory");
+				argon2parallelism = FindPreference("argon2parallelism");
+
+				aesRounds.PreferenceChange += (sender, e) => UpdateKdfSummary(e.Preference);
+				argon2rounds.PreferenceChange += (sender, e) => UpdateKdfSummary(e.Preference);
+				argon2memory.PreferenceChange += (sender, e) => UpdateKdfSummary(e.Preference);
+				argon2parallelism.PreferenceChange += (sender, e) => UpdateKdfSummary(e.Preference);
+
+	            UpdateKdfScreen();
+				
                 PrepareDefaultUsername(db);
                 PrepareDatabaseName(db);
                 PrepareMasterPassword();
 	            PrepareTemplates(db);
                 
-                Preference algorithm = FindPreference(GetString(Resource.String.algorithm_key));
-                SetAlgorithm(db, algorithm);
-
+                ListPreference algorithmPref = (ListPreference)FindPreference(GetString(Resource.String.algorithm_key));
+				algorithmPref.SetEntries(CipherPool.GlobalPool.Engines.Select(eng => eng.DisplayName).ToArray());
+				string[] algoValues = CipherPool.GlobalPool.Engines.Select(eng => eng.CipherUuid.ToHexString()).ToArray();
+				algorithmPref.SetEntryValues(algoValues);
+				algorithmPref.SetValueIndex(algoValues.Select((v, i) => new { kdf = v, index = i }).First(el => el.kdf == db.KpDatabase.DataCipherUuid.ToHexString()).index);
+				algorithmPref.PreferenceChange += AlgorithmPrefChange;
+	            algorithmPref.Summary =
+		            CipherPool.GlobalPool.GetCipher(App.Kp2a.GetDb().KpDatabase.DataCipherUuid).DisplayName;
                 UpdateImportDbPref();
                 UpdateImportKeyfilePref();
             }
@@ -425,7 +447,99 @@ namespace keepass2android
 			
         }
 
-		private void PrepareNoDonationReminderPreference(Activity ctx, PreferenceScreen screen, Preference preference)
+	    private void AlgorithmPrefChange(object sender, Preference.PreferenceChangeEventArgs preferenceChangeEventArgs)
+	    {
+			var db = App.Kp2a.GetDb();
+			var previousCipher = db.KpDatabase.DataCipherUuid;
+			db.KpDatabase.DataCipherUuid = new PwUuid(MemUtil.HexStringToByteArray((string)preferenceChangeEventArgs.NewValue));
+
+			SaveDb save = new SaveDb(Activity, App.Kp2a, new ActionOnFinish((success, message) =>
+			{
+				if (!success)
+				{
+					db.KpDatabase.DataCipherUuid = previousCipher;
+					Toast.MakeText(Activity, message, ToastLength.Long).Show();
+					return;
+				}
+				preferenceChangeEventArgs.Preference.Summary =
+					CipherPool.GlobalPool.GetCipher(db.KpDatabase.DataCipherUuid).DisplayName;
+			}));
+			ProgressTask pt = new ProgressTask(App.Kp2a, Activity, save);
+			pt.Run();
+	    }
+
+	    private void UpdateKdfScreen()
+	    {
+		    var db = App.Kp2a.GetDb();
+			var kdf = KdfPool.Get(db.KpDatabase.KdfParameters.KdfUuid);
+
+			var kdfpref = FindPreference(GetString(Resource.String.kdf_key));
+
+
+		    kdfpref.Summary = kdf.Name;
+			
+			var kdfscreen = ((PreferenceScreen)FindPreference(GetString(Resource.String.kdf_screen_key)));
+			if (kdf is AesKdf)
+			{
+				if (kdfscreen.FindPreference(GetString(Resource.String.rounds_key)) == null)
+					kdfscreen.AddPreference(aesRounds);
+				kdfscreen.RemovePreference(argon2rounds);
+				kdfscreen.RemovePreference(argon2memory);
+				kdfscreen.RemovePreference(argon2parallelism);
+
+				aesRounds.Enabled = db.CanWrite;
+				UpdateKdfSummary(aesRounds);
+			}
+			else
+			{
+				kdfscreen.RemovePreference(aesRounds);
+				if (kdfscreen.FindPreference("argon2rounds") == null)
+				{
+					kdfscreen.AddPreference(argon2rounds);
+					kdfscreen.AddPreference(argon2memory);
+					kdfscreen.AddPreference(argon2parallelism);
+				}
+				UpdateKdfSummary(argon2rounds);
+				UpdateKdfSummary(argon2memory);
+				UpdateKdfSummary(argon2parallelism);
+			}
+				
+	    }
+
+	    private void OnKdfChange(object sender, Preference.PreferenceChangeEventArgs preferenceChangeEventArgs)
+	    {
+		    var db = App.Kp2a.GetDb();
+		    var previousKdfParams = db.KpDatabase.KdfParameters;
+			Kp2aLog.Log("previous kdf: " + KdfPool.Get(db.KpDatabase.KdfParameters.KdfUuid) + " " + db.KpDatabase.KdfParameters.KdfUuid.ToHexString() );
+		    db.KpDatabase.KdfParameters =
+			    KdfPool.Get(
+				    new PwUuid(MemUtil.HexStringToByteArray((string)preferenceChangeEventArgs.NewValue)))
+				    .GetDefaultParameters();
+
+			Kp2aLog.Log("--new    kdf: " + KdfPool.Get(db.KpDatabase.KdfParameters.KdfUuid) + " " + db.KpDatabase.KdfParameters.KdfUuid.ToHexString());
+		    
+			SaveDb save = new SaveDb(Activity, App.Kp2a, new ActionOnFinish((success, message) =>
+			{
+				if (!success)
+				{
+					db.KpDatabase.KdfParameters = previousKdfParams;
+					Toast.MakeText(Activity, message, ToastLength.Long).Show();
+					return;
+				}
+				UpdateKdfScreen();
+				
+			}));
+			ProgressTask pt = new ProgressTask(App.Kp2a, Activity, save);
+			pt.Run();
+
+	    }
+
+	    private void UpdateKdfSummary(Preference preference)
+		{
+			preference.Summary = ((keepass2android.settings.KdfNumberParamPreference)preference).ParamValue.ToString();
+		}
+
+	    private void PrepareNoDonationReminderPreference(Activity ctx, PreferenceScreen screen, Preference preference)
 	    {
 			ISharedPreferences prefs = PreferenceManager.GetDefaultSharedPreferences(ctx);
 
@@ -797,12 +911,8 @@ namespace keepass2android
             return targetIoc;
         }
 
-		/*
-        private void SetRounds(Database db, Preference rounds)
-        {
-            rounds.Summary = db.KpDatabase.KeyEncryptionRounds.ToString(CultureInfo.InvariantCulture);
-        }*/
-
+		
+        
         private void SetAlgorithm(Database db, Preference algorithm)
         {
             algorithm.Summary = CipherPool.GlobalPool.GetCipher(db.KpDatabase.DataCipherUuid).DisplayName;

src/keepass2android/settings/RoundsPreference.cs

@@ -27,80 +27,68 @@ using KeePassLib.Cryptography.KeyDerivation;
 
 namespace keepass2android.settings
 {
-	/// <summary>
-	/// Represents the setting for the number of key transformation rounds. Changing this requires to save the database.
-	/// </summary>
-	public class RoundsPreference : DialogPreference {
+	public abstract class KdfNumberParamPreference: DialogPreference {
 		
-		internal TextView RoundsView;
+		internal TextView edittext;
 		
 		protected override View OnCreateDialogView() {
 			View view =  base.OnCreateDialogView();
 			
-			RoundsView = (TextView) view.FindViewById(Resource.Id.rounds);
+			edittext = (TextView) view.FindViewById(Resource.Id.rounds);
 
 
-			ulong numRounds = KeyEncryptionRounds;
-			RoundsView.Text = numRounds.ToString(CultureInfo.InvariantCulture);
+			ulong numRounds = ParamValue;
+			edittext.Text = numRounds.ToString(CultureInfo.InvariantCulture);
+
+			view.FindViewById<TextView>(Resource.Id.rounds_explaination).Text = ExplanationString;
 
 			return view;
 		}
 
-		public ulong KeyEncryptionRounds
+		public virtual string ExplanationString
 		{
-			get
-			{
-				AesKdf kdf = new AesKdf();
-				if (!kdf.Uuid.Equals(App.Kp2a.GetDb().KpDatabase.KdfParameters.KdfUuid))
-					return (uint) PwDefs.DefaultKeyEncryptionRounds;
-				else
-				{
-					ulong uRounds = App.Kp2a.GetDb().KpDatabase.KdfParameters.GetUInt64(
-						AesKdf.ParamRounds, PwDefs.DefaultKeyEncryptionRounds);
-					uRounds = Math.Min(uRounds, 0xFFFFFFFEUL);
-
-					return (uint) uRounds;
-				}
-			}
-			set { App.Kp2a.GetDb().KpDatabase.KdfParameters.SetUInt64(AesKdf.ParamRounds, value); }
+			get { return ""; }
 		}
 
-		public RoundsPreference(Context context, IAttributeSet attrs):base(context, attrs) {
+		public abstract ulong ParamValue { get; set; }
+		public KdfNumberParamPreference(Context context, IAttributeSet attrs):base(context, attrs) {
 		}
-		
-		public RoundsPreference(Context context, IAttributeSet attrs, int defStyle): base(context, attrs, defStyle) {
+
+		public KdfNumberParamPreference(Context context, IAttributeSet attrs, int defStyle)
+			: base(context, attrs, defStyle)
+		{
 		}
 		
 		protected override void OnDialogClosed(bool positiveResult) {
 			base.OnDialogClosed(positiveResult);
 			
 			if ( positiveResult ) {
-				ulong rounds;
+				ulong paramValue;
 				
-				String strRounds = RoundsView.Text; 
-				if (!(ulong.TryParse(strRounds,out rounds)))
+				String strRounds = edittext.Text; 
+				if (!(ulong.TryParse(strRounds,out paramValue)))
 				{
-					Toast.MakeText(Context, Resource.String.error_rounds_not_number, ToastLength.Long).Show();
+					Toast.MakeText(Context, Resource.String.error_param_not_number, ToastLength.Long).Show();
 					return;
 				}
 				
-				if ( rounds < 1 ) {
-					rounds = 1;
+				if ( paramValue < 1 ) {
+					paramValue = 1;
 				}
 
 				Database db = App.Kp2a.GetDb();
 
-				ulong oldRounds = KeyEncryptionRounds;
+				ulong oldValue = ParamValue;
 
-				if (oldRounds == rounds)
+				if (oldValue == paramValue)
 				{
 					return;
 				}
 
-				KeyEncryptionRounds = rounds;
+				ParamValue = paramValue;
 
 				Handler handler = new Handler();
-				SaveDb save = new SaveDb(Context, App.Kp2a, new AfterSave(Context, handler, oldRounds, this));
+				SaveDb save = new SaveDb(Context, App.Kp2a, new KdfNumberParamPreference.AfterSave(Context, handler, oldValue, this));
 				ProgressTask pt = new ProgressTask(App.Kp2a, Context, save);
 				pt.Run();
 				
@@ -111,9 +99,9 @@ namespace keepass2android.settings
 		private class AfterSave : OnFinish {
 			private readonly ulong _oldRounds;
 			private readonly Context _ctx;
-			private readonly RoundsPreference _pref;
+			private readonly KdfNumberParamPreference _pref;
 			
-			public AfterSave(Context ctx, Handler handler, ulong oldRounds, RoundsPreference pref):base(handler) {
+			public AfterSave(Context ctx, Handler handler, ulong oldRounds, KdfNumberParamPreference pref):base(handler) {
 
 				_pref = pref;
 				_ctx = ctx;
@@ -139,5 +127,54 @@ namespace keepass2android.settings
 		
 	}
 
+	/// <summary>
+	/// Represents the setting for the number of key transformation rounds. Changing this requires to save the database.
+	/// </summary>
+	public class RoundsPreference : KdfNumberParamPreference {
+		private readonly Context _context;
+
+
+		public ulong KeyEncryptionRounds
+		{
+			get
+			{
+				AesKdf kdf = new AesKdf();
+				if (!kdf.Uuid.Equals(App.Kp2a.GetDb().KpDatabase.KdfParameters.KdfUuid))
+					return (uint) PwDefs.DefaultKeyEncryptionRounds;
+				else
+				{
+					ulong uRounds = App.Kp2a.GetDb().KpDatabase.KdfParameters.GetUInt64(
+						AesKdf.ParamRounds, PwDefs.DefaultKeyEncryptionRounds);
+					uRounds = Math.Min(uRounds, 0xFFFFFFFEUL);
+
+					return (uint) uRounds;
+				}
+			}
+			set { App.Kp2a.GetDb().KpDatabase.KdfParameters.SetUInt64(AesKdf.ParamRounds, value); }
+		}
+
+		public RoundsPreference(Context context, IAttributeSet attrs):base(context, attrs)
+		{
+			_context = context;
+		}
+
+		public RoundsPreference(Context context, IAttributeSet attrs, int defStyle): base(context, attrs, defStyle)
+		{
+			_context = context;
+		}
+
+		public override string ExplanationString
+		{
+			get { return _context.GetString(Resource.String.rounds_explaination); }
+		}
+
+		public override ulong ParamValue
+		{
+			get { return KeyEncryptionRounds; }
+			set { KeyEncryptionRounds = value; }
+		}
+	
+	}
+
 }