There is no reason to believe that paper ballots aren't securable NOW and no reason to believe we will ever be able to secure electronic voting.
If you want to using cryptography print a challenge on the ballot have them type the number into 90s era flip phone sized device and have them write the response on the ballot. Without understanding anything about crypto they and the government both have half of a key and nobody can fool anyone.
Mathematically impossible to commit fraud based on math that has been given massive attention by a small army of very smart people.
Are we suggesting that rich people who get a product for free and use it to forklift more piles of money into their scrooge mcDuck like vault ought to demand more accountability from the people who provided the free forklift.
How about they pay for that?