Perhaps the election commission would also have a paper receipt with a different unique key.
Then both your receipt and the county's receipt would be necessary to locate your vote on the blockchain. Then vote verification could be restricted to the same level of privacy as when voting takes place.
I also like the idea of using 2 paper receipts which I think is easy for people to understand.
If someone would so readily hand over their SSN and Voter ID, what will stop them from handing over the county receipt?
zero-knowledge protocol is a method by which one party (the voting machine) can prove to another party (the voter) that a given statement is true (their ballot was cast, untampered), without conveying any information apart from the fact that the statement is indeed true. ... the definition implies that the voter will not be able to prove the statement in turn to anyone else (a vote buyer/intimidator), since the voter does not possess the secret information.
You can explain in about 30 seconds that the ballots shouldn't be individually identifiable, you have a record that is difficult to tamper with, etc.
How many people have a rigorous understanding of Zero Knowledge proofs? How many people would be able to audit the implementation of such a system?
The benefits that come from electronic voting are small, and we can get them in other ways. Why are people so eager to add so much complexity to such an important civic function?
I agree that a blockchain solution may be overly complex, but I think the spirit of what they're after is in the right place.
"$5 off your next purchase if you can produce a receipt for candidate X!"
"You must vote for X if you wish to join my organization."
If you are very worried about such a scenario, verify that your vote is on the blockchain, then destroy your receipt.
I don't really buy "it's illegal" as a counterargument. There are a lot of things employers pressure their employees to do that are illegal, but the employees don't really have the ability to do anything about it, because they're taking a risk on the legal system working out for them, and in the meantime they'll probably lose their job and be known as an employee who litigates against their employers. As a wise man once said, if you're a single-digit millionaire, you have no effective access to our legal system.
(And I'm sure everyone's in agreement with the importance of making the ballot secret.)