Helper to generate a random key

Generate a password or a random key (I use it to confirm newsletter unsubscribe)

<?php
//use $row->clau = $this->_helper->getHelper('Password')->generate(10, 20);
class Helper_Password extends Zend_Controller_Action_Helper_Abstract {
    ////////////////////////////////////////////////////
    //Generate a key    ////////////////////////////////////////////////////
    function generate($min = 10, $max = 20) {
        $charset = "abcdefghijklmnopqrstuvwxyzABCDEFGHIJKLMNOPQRSTUVWXYZ0123456789";
        $length = mt_rand ($min, $max);
        $key = '';
        for ($i=0; $i<$length; $i++) {
            $key .= $charset[(mt_rand(0,(strlen($charset)-1)))];   
        }
        return $key;       
    }
}