permute.php

<?php

/**
 * @param string $charset the entire set of characters to permute
 * @param array|int[] $ring an array of counters representing the character pointed to by each element of the cipher ring
 * @return Generator
 */
function permute($charset, array $ring = [0])
{
    while (count($ring) <= strlen($charset)) {
        //compile the current permutation using the ring state
        $permutation = [];
        foreach ($ring as $i => $char) {
            $permutation[$i] = $charset[$char];
        }
        yield implode('', $permutation); //convert to string and yield
        //rotate the ring by incrementing the right-mode digit
        $end = count($ring) - 1;
        $ring[$end]++;
        //working from right to left, carry all overflow to the left
        for ($i = count($ring) - 1; $i >= 0; $i--) {
            //if the digit overflows
            if ($ring[$i] > strlen($charset) - 1) {
                //reset it to zero
                $ring[$i] = 0;
                //and carry the overflow
                if (isset($ring[$i - 1])) {
                    $ring[$i - 1]++;
                } else {
                    //if we've overflowed to the start, prepend a position to the ring
                    array_unshift($ring, 0);
                }
            } else {
                break; // we didn't overflow in the bit, so no need to carry any overflow left
            }
        }
    }
}
      
$charset = '1234567890abcdefghijklmnopqrstuvwxyz';
foreach (permute($charset) as $password) {
  //do something with $password
}