src/AESGCM.php
private static function getProduct($X, $Y)
    {
        $R = pack('H*', 'E1').str_pad('', 15, "\0");
        $Z = str_pad('', 16, "\0");
        $V = $Y;

        $parts = str_split($X, 4);
        $x = sprintf('%032b%032b%032b%032b', self::toUInt32Bits($parts[0]), self::toUInt32Bits($parts[1]), self::toUInt32Bits($parts[2]), self::toUInt32Bits($parts[3]));
        $lsb_mask = "\1";
        for ($i = 0; $i < 128; $i++) {
            if ($x[$i]) {
                $Z = self::getBitXor($Z, $V);
            }
            $lsb_8 = mb_substr($V, -1, null, '8bit');
            if (ord($lsb_8 & $lsb_mask)) {
                $V = self::getBitXor(self::shiftStringToRight($V), $R);
            } else {
                $V = self::shiftStringToRight($V);
            }
        }

        return $Z;
    }
private static function getProduct($X, $Y)
    {
        $R = pack('H*', 'E1').str_pad('', 15, "\0");
        $Z = str_pad('', 16, "\0");
        $V = $Y;

        $parts = str_split($X, 4);
        $x = sprintf('%032b%032b%032b%032b', self::toUInt32Bits($parts[0]), self::toUInt32Bits($parts[1]), self::toUInt32Bits($parts[2]), self::toUInt32Bits($parts[3]));
        $lsb_mask = "\1";
        for ($i = 0; $i < 128; $i++) {
            if ($x[$i]) {
                $Z = self::getBitXor($Z, $V);
            }
            $lsb_8 = mb_substr($V, -1, null, '8bit');
            if (ord($lsb_8 & $lsb_mask)) {
                $V = self::getBitXor(self::shiftStringToRight($V), $R);
            } else {
                $V = self::shiftStringToRight($V);
            }
        }

        return $Z;
    }
@param $X
@param $Y

@return string