avoid rand() if possible as it is not generating cryptographically secure values, thx to Hanno for putting some effort into this

Signed-off-by: Michael Kaufmann (d00p) <d00p@froxlor.org>

lib/functions/system/function.randomStr.php

@@ -0,0 +1,44 @@
+<?php
+
+/**
+ * This file is part of the Froxlor project.
+ * Copyright (c) 2010 the Froxlor Team (see authors).
+ *
+ * For the full copyright and license information, please view the COPYING
+ * file that was distributed with this source code. You can also view the
+ * COPYING file online at http://files.froxlor.org/misc/COPYING.txt
+ *
+ * @copyright  (c) the authors
+ * @author     Froxlor team <team@froxlor.org> (2016-)
+ * @license    GPLv2 http://files.froxlor.org/misc/COPYING.txt
+ * @package    Functions
+ *
+ */
+
+/**
+ * Function randomStr
+ *
+ * generate a pseudo-random string of bytes
+ *
+ * @param int $length            
+ *
+ * @return string
+ */
+function randomStr($length)
+{
+    if (version_compare(PHP_VERSION, '7.0.0') >= 0) {
+        return random_bytes($length);
+    } elseif (function_exists('openssl_random_pseudo_bytes')) {
+        return openssl_random_pseudo_bytes($length);
+    } else {
+        $pr_bits = '';
+        $fp = @fopen('/dev/urandom', 'rb');
+        if ($fp !== false) {
+            $pr_bits .= @fread($fp, $length);
+            @fclose($fp);
+        } else {
+            $pr_bits = substr(rand(time()).rand(time()), 0, $length);
+        }
+        return $pr_bits;
+    }
+}