Blockchains are obviously a terrible solution to election fraud. The only thing that prevents blockchain tampering is a ton of neutral third party machines checking the transactions (typically miners). We've already seen that this is a non-trivial problem when there is plenty of incentive for random people to fulfill that role (mining of crypto currency). National elections have very little incentive for people to invest thousands in hardware and electricity, and a ton of incentive for nation states like China or Russia with the funds and technology to manipulate the results.
If you instead make it a closed system with government machines validating the results, you've not solved anything (or at least nothing that couldn't be solved with more traditional cryptographic techniques like public/private key encryption, signing, and progressive cryptographic hashing). You still haven't solved the issues of patching, of the public's trust in the machines and people involved in securing the infrastructure, or prevented a malicious third party from compromising that infrastructure and altering the results. Blockchain only provides any type of verification, when you can trust that the majority of the verifying machines are not working in league to forge results, and in a voting infrastructure of relatively well secured machines you can do a lot better. Block chain introduces a ton of extra complexity which leads to a ton of additional attack surface while again not providing a lot of value.
Finally, BlockChain does nothing to solve the issue of machines registering one vote and writing a separate vote to the ledger, or even registering multiple votes that are fraudulent. In other words, it is simply a highly inefficient tool that exists to solve an entirely different problem.
Things that would vastly improve voting security:
1) When the user comes in, check their ID to validate they are who they claim to be, and that they are allowed to vote.
2) Give them a randomly generated, complex, unguessable ID number (voteid) in the form of a QR code. This should not be tied to their identity in any way
3) Have user scan said voteid to begain voting and then store with their vote results, and give them the progressive hash of the chain of votes before and after their votes are tallied.
4) Allow the user to swipe their voteid before leaving the voting area, and view how their vote was tallied, on a separate machine (thus increasing the complexity and size of the hack required to hoodwink a cautious user).
5) Allow all users to go online and view their votes as they were recorded (and will be tallied) by entering their voteid on a public website. As well as the aforementioned progressive hashes
6) Have a process by which a user can, upon presenting their voteid contest how their votes were recorded (both at the voting place, and after the election).
Of course the progressive hash idea is someone simplistic, public/private key signing or other more complex solutions could be implemented with different risk profiles. Yes there are still ways that such a system can be hacked and manipulated, but the skill and breadth of the hack would need to be significantly increased to pull it off unnoticed. More importantly, users would be empowered to a fair degree of confidence that their vote was recorded as they intended.
