Encrypt library: xor_encode and mcrypt

[eluser]WanWizard[/eluser]
I noticed that the session library eats away quite lot of processing time for every page request.

Xdebug reveals that this is due to the calls to _xor_encode() and _xor_decode(). Is this still needed when you have mcrypt available, or could you do this instead?

Code:

function encode($string, $key = '')
{
    $key = $this->get_key($key);

    if ($this->_mcrypt_exists === TRUE)
    {
        $enc = $this->mcrypt_encode($string, $key);
    }
    else
    {
        $enc = $this->_xor_encode($string, $key);
    }

    return base64_encode($enc);
}

It seams to me that this doesn't have any serious security implications...