don't let the the user disable encryption once it was activated

settings/css/settings.css

@@ -494,3 +494,7 @@ doesnotexist:-o-prefocus, .strengthify-wrapper {
 #encryptionModules {
 	padding: 10px;
 }
+
+#warning {
+	color: red;
+}

settings/js/admin.js

@@ -55,6 +55,7 @@ $(document).ready(function(){
 	});
 
 	$('#encryptionEnabled').change(function() {
+		$('#encryptionAPI div#EncryptionWarning').toggleClass('hidden');
 		$('#encryptionAPI div#EncryptionSettingsArea').toggleClass('hidden');
 	});
 

settings/templates/admin.php

@@ -321,11 +321,15 @@ if ($_['cronErrors']) {
 	<p id="enable">
 		<input type="checkbox" name="encryption_enabled"
 			   id="encryptionEnabled"
-			   value="1" <?php if ($_['encryptionEnabled']) print_unescaped('checked="checked"'); ?> />
+			   value="1" <?php if ($_['encryptionEnabled']) print_unescaped('checked="checked" disabled="disabled"'); ?> />
 		<label
 			for="encryptionEnabled"><?php p($l->t('Enable server-side encryption')); ?> <span id="startmigration_msg" class="msg"></span> </label><br/>
 	</p>
 
+	<div id="EncryptionWarning" class="warning hidden">
+		<?php p($l->t('Once encryption is enabled there is no way to disable it again. This is your last chance to disable it again.')) ?>
+	</div>
+
 	<div id="EncryptionSettingsArea" class="<?php if (!$_['encryptionEnabled']) p('hidden'); ?>">
 		<div id='selectEncryptionModules' class="<?php if (!$_['encryptionReady']) p('hidden'); ?>">
 			<?php