code: protected function processKey($raw_key)
      {
          $key = $raw_key;
  
          if ($this->expand_and_normalize_keys) {
              $key = self::expand56BitKeyTo64BitKey($key, true);
          }
  
          return $key;
      }
docs: Process a key for DES encryption.
  
  Optionally performs an expansion and normalization process to the key.
  
  @param string $raw_key The raw key.
  @return string The processed key.