need a help

first, thanks for your useful work. it's really helpful and so clear. but when i tried the example it showed this notice:

Uninitialized string offset...

it seems to be in this line:

$code = bcadd($code, bcmul(ord($packet[$j]), bcpow('256',$j)));

please, I need your help ASAP, I'm working on my senior project.


thanks in advance

Modify it to be like this

public function encrypt ($m, $e, $n, $s=3) {
$coded = '';
$max = strlen($m);
$packets = ceil($max/$s);

for($i=0; $i<$packets; $i++){
$packet = substr($m, $i*$s, $s);
$code = '0';

for($j=0; $j<$s; $j++){
$X = substr($packet,$j,1);
$code = bcadd($code, bcmul(ord($X), bcpow('256',$j)));
}

$code = bcpowmod($code, $e, $n);
$coded .= $code.' ';
}

return trim($coded);
}

Thank you very much. This helps to solve the problem