Extraordinary rendition does indeed violate international law, hence the secretive and clandestine nature of the activity. To say otherwise is quite simply false. The whole point of the activity is to skirt the law, so of course it violates the law. It is a practice of a society that is not caring about the law.
Torture is banned, no matter where the interrogation takes place. Although it matters which country the interrogation happens, the country carrying out the interrogation should be held accountable for its actions. Torture is torture, even if certain countries have more lax laws regarding how to get information out of suspects or prisoners of war.