[Plugin: WPsupercache] wp-cache-config.php permissions

Hi i love this plugin and it works good, however i’d like to update to the latest version and there’s a problem. My wp-cache-config.php file is permissions 644 and the plugin is working, but when i deactivate it and try to activate again it says it needs to be 777 or 666. I’m not sure if it’s safe to have it 666 or 777 and i wonder why it’s working now on 644.