diff --git a/boot.php b/boot.php
index a94b380387..6373b2c64b 100644
--- a/boot.php
+++ b/boot.php
@@ -673,16 +673,6 @@ function curPageURL()
 	return $pageURL;
 }
 
-function random_digits($digits)
-{
-	$rn = '';
-	for ($i = 0; $i < $digits; $i++) {
-		/// @TODO Avoid rand/mt_rand, when it comes to cryptography, they are generating predictable (seedable) numbers.
-		$rn .= rand(0, 9);
-	}
-	return $rn;
-}
-
 function get_server()
 {
 	$server = Config::get("system", "directory");
diff --git a/include/conversation.php b/include/conversation.php
index c10a7bec73..cd635521e5 100644
--- a/include/conversation.php
+++ b/include/conversation.php
@@ -27,6 +27,7 @@ use Friendica\Util\DateTimeFormat;
 use Friendica\Util\Proxy as ProxyUtils;
 use Friendica\Util\Temporal;
 use Friendica\Util\XML;
+use Friendica\Util\Crypto;
 
 function item_extract_images($body) {
 
@@ -1166,7 +1167,7 @@ function status_editor(App $a, $x, $notes_cid = 0, $popup = false)
 		'$notes_cid'    => $notes_cid,
 		'$sourceapp'    => L10n::t($a->sourcename),
 		'$cancel'       => L10n::t('Cancel'),
-		'$rand_num'     => random_digits(12),
+		'$rand_num'     => Crypto::randomDigits(12),
 
 		// ACL permissions box
 		'$acl'           => $x['acl'],
diff --git a/mod/editpost.php b/mod/editpost.php
index 0023e35edd..b518588a59 100644
--- a/mod/editpost.php
+++ b/mod/editpost.php
@@ -12,6 +12,7 @@ use Friendica\Core\System;
 use Friendica\Model\FileTag;
 use Friendica\Model\Item;
 use Friendica\Database\DBA;
+use Friendica\Util\Crypto;
 
 function editpost_content(App $a)
 {
@@ -131,7 +132,7 @@ function editpost_content(App $a)
 		'$jotplugins' => $jotplugins,
 		'$sourceapp' => L10n::t($a->sourcename),
 		'$cancel' => L10n::t('Cancel'),
-		'$rand_num' => random_digits(12),
+		'$rand_num' => Crypto::randomDigits(12),
 
 		//jot nav tab (used in some themes)
 		'$message' => L10n::t('Message'),
diff --git a/mod/photos.php b/mod/photos.php
index 69b1972d4c..7a49f061a7 100644
--- a/mod/photos.php
+++ b/mod/photos.php
@@ -26,6 +26,7 @@ use Friendica\Model\User;
 use Friendica\Network\Probe;
 use Friendica\Object\Image;
 use Friendica\Protocol\DFRN;
+use Friendica\Util\Crypto;
 use Friendica\Util\DateTimeFormat;
 use Friendica\Util\Map;
 use Friendica\Util\Security;
@@ -1500,7 +1501,7 @@ function photos_content(App $a)
 						'$preview' => L10n::t('Preview'),
 						'$sourceapp' => L10n::t($a->sourcename),
 						'$ww' => '',
-						'$rand_num' => random_digits(12)
+						'$rand_num' => Crypto::randomDigits(12)
 					]);
 				}
 			}
@@ -1539,7 +1540,7 @@ function photos_content(App $a)
 						'$preview' => L10n::t('Preview'),
 						'$sourceapp' => L10n::t($a->sourcename),
 						'$ww' => '',
-						'$rand_num' => random_digits(12)
+						'$rand_num' => Crypto::randomDigits(12)
 					]);
 				}
 
@@ -1599,7 +1600,7 @@ function photos_content(App $a)
 							'$preview' => L10n::t('Preview'),
 							'$sourceapp' => L10n::t($a->sourcename),
 							'$ww' => '',
-							'$rand_num' => random_digits(12)
+							'$rand_num' => Crypto::randomDigits(12)
 						]);
 					}
 				}
diff --git a/src/Core/System.php b/src/Core/System.php
index 0f9a611ab9..d24581e996 100644
--- a/src/Core/System.php
+++ b/src/Core/System.php
@@ -265,7 +265,6 @@ class System extends BaseObject
 	function notice($s)
 	function info($s)
 	function is_site_admin()
-	function random_digits($digits)
 	function get_server()
 	function get_temppath()
 	function get_cachefile($file, $writemode = true)
diff --git a/src/Object/Post.php b/src/Object/Post.php
index e2c1ea03c3..644d53e25d 100644
--- a/src/Object/Post.php
+++ b/src/Object/Post.php
@@ -18,6 +18,7 @@ use Friendica\Database\DBA;
 use Friendica\Model\Contact;
 use Friendica\Model\Item;
 use Friendica\Model\Term;
+use Friendica\Util\Crypto;
 use Friendica\Util\DateTimeFormat;
 use Friendica\Util\Proxy as ProxyUtils;
 use Friendica\Util\Temporal;
@@ -815,7 +816,7 @@ class Post extends BaseObject
 				'$indent'      => $indent,
 				'$sourceapp'   => L10n::t($a->sourcename),
 				'$ww'          => $conv->getMode() === 'network' ? $ww : '',
-				'$rand_num'    => random_digits(12)
+				'$rand_num'    => Crypto::randomDigits(12)
 			]);
 		}
 
diff --git a/src/Util/Crypto.php b/src/Util/Crypto.php
index 2b1ce0f02b..785860c182 100644
--- a/src/Util/Crypto.php
+++ b/src/Util/Crypto.php
@@ -476,4 +476,30 @@ class Crypto
 
 		return self::decryptAES256CBC(base64url_decode($data['data']), $k, $i);
 	}
+
+
+	/**
+	 * Creates cryptographic secure random digits
+	 *
+	 * @param string $digits The count of digits
+	 * @return int The random Digits
+	 */
+	public static function randomDigits($digits)
+	{
+		$rn = '';
+
+		if (!function_exists('random_int')) {
+			// using rand() function for PHP 5.x compatibility
+			for ($i = 0; $i < $digits; $i++) {
+				$rn .= rand(0, 9);
+			}
+		} else {
+			// generating cryptographically secure pseudo-random integers
+			for ($i = 0; $i < $digits; $i++) {
+				$rn .= random_int(0, 9);
+			}
+		}
+
+		return $rn;
+	}
 }
diff --git a/tests/src/Util/CryptoTest.php b/tests/src/Util/CryptoTest.php
new file mode 100644
index 0000000000..d014d28182
--- /dev/null
+++ b/tests/src/Util/CryptoTest.php
@@ -0,0 +1,131 @@
+<?php
+
+// this is in the same namespace as Install for mocking 'rand' and 'random_init'
+namespace Friendica\Util;
+
+use PHPUnit\Framework\TestCase;
+
+class CryptoTest extends TestCase
+{
+	/**
+	 * Replaces function_exists results with given mocks
+	 *
+	 * @param array $functions a list from function names and their result
+	 */
+	private function setFunctions($functions)
+	{
+		global $phpMock;
+		$phpMock['function_exists'] = function($function) use ($functions) {
+			foreach ($functions as $name => $value) {
+				if ($function == $name) {
+					return $value;
+				}
+			}
+			return '__phpunit_continue__';
+		};
+	}
+
+	/**
+	 * Replaces rand results with given mocks
+	 *
+	 */
+	private function assertRand($min, $max)
+	{
+		global $phpMock;
+		$phpMock['rand'] = function($mMin, $mMax) use ($min, $max) {
+			$this->assertEquals($min, $mMin);
+			$this->assertEquals($max, $mMax);
+			return 1;
+		};
+	}
+
+	/**
+	 * Replaces rand results with given mocks
+	 *
+	 */
+	private function assertRandomInt($min, $max)
+	{
+		global $phpMock;
+		$phpMock['random_int'] = function($mMin, $mMax) use ($min, $max) {
+			$this->assertEquals($min, $mMin);
+			$this->assertEquals($max, $mMax);
+			return 1;
+		};
+	}
+
+	public function testRandomDigitsRand()
+	{
+		$this->setFunctions(['random_int' => false]);
+		$this->assertRand(0, 9);
+
+		$test = Crypto::randomDigits(1);
+		$this->assertEquals(1, strlen($test));
+		$this->assertEquals(1, $test);
+
+		$test = Crypto::randomDigits(8);
+		$this->assertEquals(8, strlen($test));
+		$this->assertEquals(11111111, $test);
+	}
+
+
+	public function testRandomDigitsRandomInt()
+	{
+		$this->setFunctions(['random_int' => true]);
+		$this->assertRandomInt(0, 9);
+
+		$test = Crypto::randomDigits(1);
+		$this->assertEquals(1, strlen($test));
+		$this->assertEquals(1, $test);
+
+		$test = Crypto::randomDigits(8);
+		$this->assertEquals(8, strlen($test));
+		$this->assertEquals(11111111, $test);
+	}
+}
+
+/**
+ * A workaround to replace the PHP native function_exists() with a mocked function
+ *
+ * @param string $function_name the Name of the function
+ *
+ * @return bool true or false
+ */
+function function_exists($function_name)
+{
+	global $phpMock;
+	if (isset($phpMock['function_exists'])) {
+		$result = call_user_func_array($phpMock['function_exists'], func_get_args());
+		if ($result !== '__phpunit_continue__') {
+			return $result;
+		}
+	}
+	return call_user_func_array('\function_exists', func_get_args());
+}
+
+/**
+ * A workaround to replace the PHP native rand() (< 7.0) with a mocked function
+ *
+ * @return int
+ */
+function rand($min, $max)
+{
+	global $phpMock;
+	if (isset($phpMock['rand'])) {
+		$result = call_user_func_array($phpMock['rand'], func_get_args());
+		return $result;
+	}
+}
+
+/**
+ * A workaround to replace the PHP native random_int() (>= 7.0) with a mocked function
+ *
+ * @return int
+ */
+function random_int($min, $max)
+{
+	global $phpMock;
+	if (isset($phpMock['random_int'])) {
+		$result = call_user_func_array($phpMock['random_int'], func_get_args());
+		return $result;
+	}
+}