How might you hack this voting protocol?
There is a society with about the same technological development as we have today, but they are more civically-minded and more astute when it comes to security issues. They are also democratic and want to ensure their democratic process is secure.
Here's how they vote.
* Voters arrive at a public space in their local area. They present their credentials to an administrator and, if that checks out, reach into a bucket of barcoded tokens and take one at random. Each token activates a voting machine for a single use.
* The list of who has and has not voted is made public at the end and leftover activation tokens are counted in public view.
* The machines are in hooded boothes in the same room. Outside each booth is a prominent display counter which increments each time someone casts a ballot.
* Inside the booth, the voter feeds the activation token to the machine. They enter their preference(s) and the machine prints a paper slip which contains this information.
* The confirmation slip stays within the machine but is visible through a plastic window. It remains in place so the voter can choose to confirm or shred it in case of a mistake.
* If confirmed, the slip falls face-down onto a stack of previous voters' slips. The container is transparent.
* When some number, say 500, of votes have been entered, the box is sealed and the totals are electronically broadcast. 89
An attendant takes the transparent box of slips out into the room and shakes it vigorously to disorder the slips. The full box is left in public view and an empty box is set into the machine for further use.
* When voting is over, in public view, attendants visit each container in turn and toss a handful of coins (say, 5) and if all of them come up heads then the box is opened and the count checked manually. This all happens in the same room, in front of everyone. The confirmation slips are anonymous and the count should be exact. At least one container in each room must be checked, so this process is repeated until the coin toss chooses at least one.
The people in this society have a high degree of confidence in the security of their elections. How might they be caught out?
This system has at least one vulnerability that I can see: the administrators could forge credentials to allow fictitious people to vote, but the population also anticipated this and volunteers run footage of voters through facial recognition software to red-flag similar faces for closer inspection. They know this isn't perfect, but it raises the bar somewhat. Also, the government as a whole is not expected to be so hostile (although individuals within it may be).
How else might an imaginative adversary subvert the voting process?
EDIT Thanks everyone for your insight. I'm not going to nominate a "correct" answer since it's such an open question, but have an upvote :-) 89