You're probably referring to https://news.ycombinator.com/item?id=5482178
26 karma · joined March 9, 2012
You are presented with
* * [ ] * [ ] * * [ ]
and you are supposed to submit
* * [3] * [5] * * [8]
so neither side would have enough information to reconstruct the full password based on the user's input alone.
[1] http://newcoursys.herokuapp.com/courses/2012sp-cmpt-165-c1/a... [2] http://newcoursys.herokuapp.com/#marking-interface
http://www.securelist.com/en/blog/667/The_Mystery_of_the_Duq...