I propose that, for the people to trust their democracy, they must be able to understand all aspects of the voting system. This rules out pretty well all automated systems, especially computers with cryptography and hashes. Just go back to people writing on paper and ballot boxes.
Sure counting the ballots by hand is expensive but it's tiny compared to the cost of travel and time for the voters. The risk of serious, undetected fixing of results can't be eliminated with automated systems.