Yes, several. A particularly interesting one is Scantegrity [1]: > Scantegrity is a security enhancement for optical scan voting systems, providing such system

Yes, several. A particularly interesting one is Scantegrity [1]: > Scantegrity is a security enhancement for optical scan voting systems, providing such systems with end-to-end (E2E) verifiability of election results. It uses confirmation codes to allow a voter to prove to themselves that their ballot is included unmodified in the final tally. The codes are privacy-preserving and offer no proof of which candidate a voter voted for. Receipts can be safely shown without compromising ballot secrecy. > Scantegrity II prints the confirmation codes in invisible ink to improve usability and dispute resolution. As the system relies on cryptographic techniques, the ability to validate an election outcome is both software independent as well as independent of faults in the physical chain-of-custody of the paper ballots. The system was developed by a team of researchers including cryptographers David Chaum and Ron Rivest. It works with the common "fill in the bubble" paper ballots that can be counted by simple optical scanners (or by hand). The only extra hardware you need to add it to an existing "fill in the bubble" system is that you have to use a special marker to fill in the bubbles. Here's a paper giving details [2]. Here's a paper proving coercion resistance [3]. [1] https://en.wikipedia.org/wiki/Scantegrity https://en.wikipedia.org/wiki/Scantegrity [2] https://www.usenix.org/legacy/event/evt08/tech/full_papers/chaum/chaum_html/index.html https://www.usenix.org/legacy/event/evt08/tech/full_papers/c... [3] https://eprint.iacr.org/2010/502.pdf https://eprint.iacr.org/2010/502.pdf