How to decrypt password from roundcube session?

Question

Roundcube

There is a table session in the roundcube database, my session is stored there and encrypted (in 3des if I'm not mistaken the password to it) -
imap_ssl|N;password|s:32:"32characters"
I have $rcmail_config['des_key']
cbc
What I still need to decrypt it and how to do it.
Online services for examples ask for some kind of IV. where to get it from?
here is the decryptor code

public function decrypt($cipher, $key = 'des_key', $base64 = true)
  {
    if (!$cipher)
      return '';

    $cipher = $base64 ? base64_decode($cipher) : $cipher;

    if (function_exists('mcrypt_module_open') &&
        ($td = mcrypt_module_open(MCRYPT_TripleDES, "", MCRYPT_MODE_CBC, "")))
    {
      $iv_size = mcrypt_enc_get_iv_size($td);
      $iv = substr($cipher, 0, $iv_size);

      // session corruption? (#1485970)
      if (strlen($iv) < $iv_size)
        return '';

      $cipher = substr($cipher, $iv_size);
      mcrypt_generic_init($td, $this->config->get_crypto_key($key), $iv);
      $clear = mdecrypt_generic($td, $cipher);
      mcrypt_generic_deinit($td);
      mcrypt_module_close($td);
    }
    else {
      @include_once 'des.inc';

      if (function_exists('des')) {
        $des_iv_size = 8;
        $iv = substr($cipher, 0, $des_iv_size);
        $cipher = substr($cipher, $des_iv_size);
        $clear = des($this->config->get_crypto_key($key), $cipher, 0, 1, $iv);
      }
      else {
        raise_error(array(
          'code' => 500, 'type' => 'php',
          'file' => __FILE__, 'line' => __LINE__,
          'message' => "Could not perform decryption; make sure Mcrypt is installed or lib/des.inc is available"
        ), true, true);
      }
    }

    /*-
     * Trim PHP's padding and the canary byte; see note in
     * rcmail::encrypt() and http://php.net/mcrypt_generic#68082
     */
    $clear = substr(rtrim($clear, "\0"), 0, -1);

    return $clear;
  }

  /**
   * Generates encryption initialization vector (IV)
   *
   * @param int Vector size
   * @return string Vector string
   */
  private function create_iv($size)
  {
    // mcrypt_create_iv() can be slow when system lacks entrophy
    // we'll generate IV vector manually
    $iv = '';
    for ($i = 0; $i < $size; $i++)
        $iv .= chr(mt_rand(0, 255));
    return $iv;
  }

Answer 1

You have before your eyes a code in which you can clearly see where iv comes from

$des_iv_size = 8;
        $iv = substr($cipher, 0, $des_iv_size);