function keygen($length) {
    $token = '';
    $tokenlength = round($length * 4 / 3);
    for ($i = 0; $i < $tokenlength; ++$i) {
        $token .= chr(rand(32, 1024));
    }
    $token = base64_encode(str_shuffle($token));
    return substr($token, 0, $length);
}