PHP XOR encryption and decryption

XOR is a logical operation, pronounced exclusive or. It can be used to cipher messages simply and fast.

<?php 
$xor_key = 's9k7a8l4j';
$string = 'string';

function xorIt($string, $key, $type = 0)
{
        $sLength = strlen($string);
        $xLength = strlen($key);
        for($i = 0; $i < $sLength; $i++) {
                for($j = 0; $j < $xLength; $j++) {
                        if ($type == 1) {
                                //decrypt
                                $string[$i] = $key[$j]^$string[$i];
                                
                        } else {
                                //crypt
                                $string[$i] = $string[$i]^$key[$j];
                        }
                }
        }
        return $string;
}

$signal = base64_encode(xorIt($string, $xor_key));
echo $signal . PHP_EOL;

$string = xorIt(base64_decode($signal), $xor_key, 1);
echo $string . PHP_EOL;