Verify the vote
Each citizen can verify the vote. State needs to generate a file containing all votes and their signature (maybe other stuff ?) and sign this file. The signature of this file is publish to all people, so everybody knows that they are verifying the same data. If the state signed two files, then the state is corrupted.
The citizen can check its vote is in the file and not modified. He can also calculate the result of the vote by aggregating all votes.
The party should also verify that all citizens are valid. No new people, dead people ...