I’ve been asked about a number of ideas lately involving voting systems and blockchains. This blog piece talks about all the security properties that a voting system needs to have, where blockchains help, and where they don’t. Let’s start off a decade ago, when Daniel Sandler and I first wrote a paper saying blockchains would be useful for voting systems. We observed that voting machines running on modern computers have overwhelming amounts of CPU and storage, so let’s use it in a serious way. Let’s place a copy of every vote on every machine and let’s use timeline entanglement (Maniatis and Baker 2002), so every machine’s history is protected by hashes stored on other machines. We even built a prototype voting system called VoteBox that used all of this, and many of the same ideas now appear in a design called STAR-Vote, which we hope could someday be used by real voters in real elections.
What is a blockchain good for? Fundamentally, it’s about having a tamper-evident history of events. In the context of a voting system, this means that a blockchain is a great place to store ballots to protect their integrity. STAR-Vote and many other “end-to-end” voting systems have a concept of a “public bulletin board” where encrypted votes go, and a blockchain is the obvious way to implement the public bulletin board. Every STAR-Vote voter leaves the polling place with a “receipt” which is really just the hash of their encrypted ballot, which in turn has the hash of the previous ballot. In other words, STAR-Vote voters all leave the polling place with a pointer into the blockchain which can be independently verified. … Achieving a “cast as intended” property requires a variety of mechanisms ranging from paper ballots and spot challenges of machines. The blockchain protects the integrity of the recorded vote, but has nothing to say about its fidelity to the intent of the voter.