It could be possible to have a system like:
If you wish, you can write a phrase on your ballot. The phrases and their corresponding vote are broadcast (on tv, internet, etc). So if you want to validate that your vote was tallied correctly, write a unique phrase. Or you could pick a random 30 digit number, collisions should be zero-probability, right?
I mean, this would be annoying because people would write slurs and advertisements, and the government would have to broadcast them. But, it seems pretty robust.
I’d suggest the state handle the number issuing, but then they could record who they issues which numbers to, and the winning party could go about rounding up their opposition, etc.
Voting systems require that there be no way to prove that you voted a certain way, otherwise it opens the market for vote-selling.
Hmm, good point.
Googling around a bit, it sounds like there are systems that let you verify that your ballot made it, but not necessarily that it was counted correctly. (For this reason, I guess?)