Two ways: 1. Votes can replace older votes - although this has issues because they could just make sure you don't vote again by pulling the trigger. 2. Let th

Two ways: 1. Votes can replace older votes - although this has issues because they could just make sure you don't vote again by pulling the trigger. 2. Let the voter assign 1 and 2 to A and B himself when receiving the private key - which means that when the time to click 1 or 2 comes - only the voter knows if 1 => A or 1 => B which makes it impossible to know who he is voting for.