This is a real problem! The secret vote isn't just about making sure that you can choose privately, but also about making sure that other people don't have ways of coercing you into certain choices.
Consider the simplest case, a binary choice. The system tells you (and only you, and only once and without tangible record) that the public copy will either be inverted or not, a one bit one time pad. Kind of feasible, but already hard enough: will you really assume tampering when the bit that makes the public record match your vote does not match your memory? Then imagine scaling to something more meaningful than a binary vote, even just to more than one binary. I can't see that actually working out.
They are given two random words. One for candidate A, one for candidate B.
They are told they should remember the code-word matching their choice if they later want to scan the printed out QR code (or enter their vote uuid) to one of the validator websites.
Voter makes their choice, completes the process. A thermal printout is printed with their vote uuid and a QR code meant to make it easy to input it.
Now anyone can get that printout with the uuid and scan it and see the code-word representing the voter's selection. However the association is only known to the voter and if asked, the voter can say that's what it was.
never said it's easy, but it is possible.
I've been thinking for a while that it would be nice to have paper ballots with the ability to cryptographically verify the inclusion of your vote in totals all the way up (ballot collection box, polling location, district, city, county, state, nation).
So the Australian Senate is currently vulnerable to vote buying, for what it's worth.
https://www.zdnet.com/google-amp/article/us-voter-records-fr...
https://gizmodo.com/nearly-15-million-texas-voters-reportedl...
https://thestack.com/security/2016/04/25/93-4-million-mexica...
So much for such an important feature.
I’m not sure if there’s a way around that, but it would be awesome to be able to absolutely prove all votes were correctly counted.
At every step of this way, if there is software involved it becomes instantly easier and less risky to influence. Whether it is online voting, voting machines, vote counting software, tabulation software, emailing results upwards etc.
To make all this work the paper and electronic trail is digitally signed with something that's only on your voting card.