I'm sorry, but please follow the current state of the discussion which probably is the opinion of the constitutional court of Germany.
Essentially they found that it's rather irrelevant how secure it is, what's important is that it's easy to detect fraud. And by being easy they mean that a lay person without any special knowledge can, without a doubt, find out when fraud occurred.
The typical well designed system is the hand marked paper ballot. The technique to check for fraud is trivial. You look into the ballot box before the election to make sure it's empty, you make sure everybody just throws one ballot into the box, you make sure that in the end the number of ballots is equal to the number of people voting, and then you make sure everything is counted correctly. The last part is hard to watch, but since the ballots are stored you can always have a recount.
Compare that to those mathematical systems which, even if you understand the math, require you to actually see what computers are doing. So essentially you need to do a deep forensic analysis on a voting computer checking everything from the firmware to the individual dies of the chips.
Other areas as in banking have it easier. There you can just have audit logs for everything and check against such logs. This cannot be done with elections because of voter privacy which is highly important by itself.