Mask credit card number in PHP

You can use substr_replace

$var = '1234123412341234';
$var = substr_replace($var, str_repeat("X", 8), 4, 8);
echo $var;

Output

1234XXXXXXXX1234

This should work using substr:

function ccMasking($number, $maskingCharacter = 'X') {
    return substr($number, 0, 4) . str_repeat($maskingCharacter, strlen($number) - 8) . substr($number, -4);
}