I'd like to verify knowledge about your private password, without it being shared. Sounds good? OK, my first question: does it start with an "a"? No? What about

I'd like to verify knowledge about your private password, without it being shared. Sounds good? OK, my first question: does it start with an "a"? No? What about a "b"? How can you verify something about someone's criminal background that doesn't ultimately share the information?