Because if you can prove to a third-party how you voted, you can sell your vote, or coerce someone else to vote a certain way.
It's one of the biggest challenges in crypto-voting systems. And there are some solutions. But we need to hammer down on the "silly people, why not just print a receipt" idea really hard.
It's one of the biggest challenges in crypto-voting systems. And there are some solutions. But we need to hammer down on the "silly people, why not just print a receipt" idea really hard.