End-to-end auditable voting systems

End-to-end auditable or end-to-end voter verifiable (E2E) systems are voting systems with stringent integrity properties and strong tamper resistance. E2E systems often employ cryptographic methods to craft receipts that allow voters to verify that their votes were counted as cast, without revealing which candidates were voted for. As such, these systems are sometimes referred to as receipt-based systems.

Electronic voting systems arrive at their final vote totals by a series of steps:

Classical approaches to election integrity tended to focus on mechanisms that operated at each step on the chain from voter intent to final total. Voting is an example of a distributed system, and in general, distributed system designers have long known that such local focus may miss some vulnerabilities while over-protecting others. The alternative is to use end-to-end measures that are designed to guard the integrity of the entire chain.

The failure of current optical scan voting systems to meet reasonable end-to-end standards was pointed out in 2002.

Comprehensive coverage of election integrity frequently involves multiple stages. Voters are expected to verify that they have marked their ballots as intended, we use recounts or audits to protect the step from marked ballots to ballot-box totals, and we use publication of all subtotals to allow public verification that the overall totals correctly sum the local totals.

While measures such as voter verified paper audit trails and manual recounts increase the effectiveness of our defenses, they offer only weak protection of the integrity of the physical or electronic ballot boxes. Ballots could be removed, replaced, or could have marks added to them (i.e.,to fill in undervoted contests with votes for a desired candidate or to overvote and spoil votes for undesired candidates). This shortcoming motivated the development of the end-to-end auditable voting systems discussed here, sometimes referred to as E2E voting systems. These attempt to cover the entire path from voter attempt to election totals with just two measures:

Because of the importance of the right to a secret ballot, all of the interesting E2E voting schemes also attempt to meet a third requirement, usually referred to as receipt freeness:

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