function invMixColumns($state)
{
$s_prime = array();
for ($i = 0; $i < sizeof($state); $i++) {
#for each column in the state
$column = array();
foreach ($state as $index => $row) {
#get the column
$column[] = $row[$i];
}
foreach ($this->invMixState as $index => $row) {
#matrix multiplication
if (!array_key_exists($index, $s_prime)) {
$s_prime[$index] = array();
}
$next = array();
for ($j = 0; $j < sizeof($column); $j++) {
$next[] = AES::ffMultiply($column[$j], $row[$j]);
}
for ($j = 1; $j < sizeof($next); $j++) {
$first = str_pad(base_convert($next[0], 16, 2), 8, "0", STR_PAD_LEFT);
$second = str_pad(base_convert($next[$j], 16, 2), 8, "0", STR_PAD_LEFT);
$next[0] = AES::ffAdd($first, $second);
}
$s_prime[$index][] = $next[0];
}
}
// $this->printState($s_prime);
return $s_prime;
}
