Vote Verification using CAPTCHAs

Recently proposed voter-verifiable protocols provide encrypted paper receipts to voters, who may later check that these receipts are in the electronic ballot box. This paper describes an enhancement that allows the voter to electronically transmit, from the polling booth, her encrypted receipt to an external verifier, who may perform the check on her behalf. It uses CAPTCHAs (techniques whose security depends on the hardness of an AI problem) to enable the voter to be certain that the receipt has been securely deposited with the external verifier. This approach presents several advantages: the voter is not required to do anything outside the polling booth, no receipts are needed after polling, and all receipts can be checked. Additionally, an audio-based format is an easy extension for those with visual disabilities, and it is anticipated that a public already familiar with CAPTCHAs will find the enhancement easy to use.