raddit.php

<?php

$encrypted_block = 'PKklQOstCkI=';

$message = '';
$charset = '_-abcdefghijklmnopqrstuvwxyz0123456789';
$str_length = strlen($charset);
$method = 'DES-ECB';

function check($flag) {
  global $message, $method, $encrypted_block;
  $crypto = openssl_encrypt($message, $method, $flag);
  if ($crypto == $encrypted_block) {
    echo $flag;
    exit;
  }
}

function recurse($width, $position, $base_string) {
  global $charset, $str_length;
 
  for ($i = 0; $i < $str_length; ++$i) {
    if ($position  < $width - 1) {
      recurse($width, $position + 1, $base_string . $charset[$i]);
    }
    check($base_string . $charset[$i]);
  }
}
 
for ($i = 1; $i < 8 + 1; ++$i) {
  echo "start $i";
  recurse($i, 0, '');
}