Maybe you could adapt this implicit memory-based authentication scheme into a board game format similar to Mastermind.
Recognition memory is actually even cooler than implicit memory, I thought, and can contain quite a bit of information (as far as I could tell, working through Shannon's theorem): http://www.gwern.net/Spaced%20repetition#fn63
Dunno how it would work in this setting, though, unless the personalities share visual recognition.
If it's worth saying, but not worth its own post, even in Discussion, it goes here.