public static function hash($str, $salt = '', $plain = false)
    {
        $size = 512;
        $rounds = 1;
        if (strncmp($salt, '$', 1) === 0) {
            $e = explode('$', $salt, 3);
            $ee = explode('=', $e[1]);
            if (ctype_digit($ee[0])) {
                $size = (int)$e[1];
            }
            if (isset($ee[1]) && ctype_digit($e[1])) {
                $size = (int)$e[1];
            }
        }
        $hash = $str . $salt;
        if ($rounds < 1) {
            $rounds = 1;
        } elseif ($rounds > 128) {
            $rounds = 128;
        }
        for ($i = 0; $i < $rounds; ++$i) {
            $hash = \keccak_hash($hash, $size);
        }
        if ($plain) {
            return $hash;
        }
        return base64_encode($hash);
    }