public function curvePointOctets(): array
    {
        if ($this->isCompressed()) {
            throw new \RuntimeException("EC point compression not supported.");
        }
        $str = substr($this->_ecPoint, 1);
        list($x, $y) = str_split($str, (int) floor(strlen($str) / 2));
        return [$x, $y];
    }