public function toBinary()
    {
        $aces = '';
        foreach ($this->aces as $ace) {
            $aces .= $ace->toBinary();
        }

        return pack(
            'C1C1v1v1v1',
            $this->revision,
            $this->sbz1,
            ((16 + (strlen(bin2hex($aces)))) / 2),
            count($this->aces),
            $this->sbz2
        ).$aces;
    }