Mimicry and meeting halfway
Paul Christiano

Hey there!

Interesting idea, very similar to what I was presenting here: http://lesswrong.com/lw/mqc/chatbots_or_set_answers_not_wbes/

The main difference is that I allow then to construct a probability distribution over answers, and Eve must achieve a certain level of certainty in distinguishing A and H, not just better than random.