Earlier quoted context omitted.
The correctness of cryptographic voting systems is determined by their publicly observable behavior, not by their internal implementation. It's the protocol that's secure, not the specific hardware or software implementation. So the attack you're describing doesn't really apply.
But you cannot observe it. You see that someone with a hash X has voted. How do you know whether it was a real person, a real person voting under boss supervision, a real person who actually didn't take part in elections, or just sysadmin inserting records into the database?
- You can somehow identify your own vote and thus verify it was properly counted
- Everyone else can do the same, thus fraudsters would have to find a protocol weakness to add additional votes
One attack vector might be whatever you use to identify your vote. Aka find a way to make two people think the same record is their own vote, then use the other yourself. This seems like a tricky problem, since everyone shouldn't just be able to see their own vote was included but also not not be able to show others how you voted. The article seems to indicate they solved this somehow, but I'm not familiar enough with the details / homomorphic encryption to understand that or even just trust that specific kind of encryption.