diff --git a/phpstan.neon b/phpstan.neon
index c9f147be..d5448c07 100644
--- a/phpstan.neon
+++ b/phpstan.neon
@@ -4,6 +4,7 @@ includes:
 parameters:
 	tmpDir: /tmp/phpstan-corelibs
 	level: 8 # max is now 9
+	checkMissingCallableSignature: true
 	paths:
 		- %currentWorkingDirectory%/www
 	bootstrapFiles:
diff --git a/www/admin/class_test.randomkey.php b/www/admin/class_test.randomkey.php
index de335b20..c91ffcd4 100644
--- a/www/admin/class_test.randomkey.php
+++ b/www/admin/class_test.randomkey.php
@@ -50,11 +50,13 @@ print '<div><a href="class_test.php">Class Test Master</a></div>';
 
 $key_length = 10;
 $key_length_b = 5;
+$key_lenght_long = 64;
 print "S::RANDOMKEYGEN(auto): " . RandomKey::randomKeyGen() . "<br>";
 print "S::SETRANDOMKEYLENGTH($key_length): " . RandomKey::setRandomKeyLength($key_length) . "<br>";
 print "S::RANDOMKEYGEN($key_length): " . RandomKey::randomKeyGen() . "<br>";
 print "S::RANDOMKEYGEN($key_length_b): " . RandomKey::randomKeyGen($key_length_b) . "<br>";
 print "S::RANDOMKEYGEN($key_length): " . RandomKey::randomKeyGen() . "<br>";
+print "S::RANDOMKEYGEN($key_lenght_long): " . RandomKey::randomKeyGen($key_lenght_long) . "<br>";
 $_array = new CoreLibs\Create\RandomKey();
 print "C->RANDOMKEYGEN(auto): " . $_array->randomKeyGen() . "<br>";
 // DEPRECATED
diff --git a/www/lib/CoreLibs/Convert/Colors.php b/www/lib/CoreLibs/Convert/Colors.php
index f565ebda..7e519357 100644
--- a/www/lib/CoreLibs/Convert/Colors.php
+++ b/www/lib/CoreLibs/Convert/Colors.php
@@ -10,6 +10,9 @@
  * hsl to rgb
 */
 
+// TODO: use oklab as base for converting colors
+// https://bottosson.github.io/posts/oklab/
+
 declare(strict_types=1);
 
 namespace CoreLibs\Convert;
diff --git a/www/lib/CoreLibs/Create/RandomKey.php b/www/lib/CoreLibs/Create/RandomKey.php
index 80c476c7..e3c7aa32 100644
--- a/www/lib/CoreLibs/Create/RandomKey.php
+++ b/www/lib/CoreLibs/Create/RandomKey.php
@@ -11,8 +11,8 @@ namespace CoreLibs\Create;
 class RandomKey
 {
 	// key generation
-	/** @var array<mixed> */
-	private static $key_range = [];
+	/** @var string */
+	private static $key_range = '';
 	/** @var int */
 	private static $one_key_length;
 	/** @var int */
@@ -33,9 +33,13 @@ class RandomKey
 	 */
 	private static function initRandomKeyData()
 	{
-		// random key generation
-		self::$key_range = array_merge(range('A', 'Z'), range('a', 'z'), range('0', '9'));
-		self::$one_key_length = count(self::$key_range);
+		// random key generation base string
+		self::$key_range = join('', array_merge(
+			range('A', 'Z'),
+			range('a', 'z'),
+			range('0', '9')
+		));
+		self::$one_key_length = strlen(self::$key_range);
 	}
 
 	/**
@@ -103,11 +107,11 @@ class RandomKey
 		} else {
 			$use_key_length = self::$key_length;
 		}
-
-		$pieces = [];
+		// create random string
+		$random_string = '';
 		for ($i = 1; $i <= $use_key_length; $i++) {
-			$pieces[] = self::$key_range[random_int(0, self::$one_key_length - 1)];
+			$random_string .= self::$key_range[random_int(0, self::$one_key_length - 1)];
 		}
-		return join('', $pieces);
+		return $random_string;
 	}
 }