And if it could tell you that then a third party could force you to reveal that you voted "right" as agreed before.

Paper ballots with mutually suspicious representatives of all parties watching themselves during handling and counting is the only way to go for big things like parliament/presidential elections and national referendums where, in the worst case, the greatest of all matters are at stake. And foolproof method for voting is most needed when the levels of trust are at the lowest.