July 18, 2019

BMDs are not meaningfully auditable

This paper has just been released on SSRN. In this paper we analyze, if a BMD were hacked to cheat, to print rigged votes onto the paper ballot; and even suppose voters carefully inspected their ballots (which most voters don’t do), and even supposing a voter noticed that the wrong vote was printed, what then? To assess this question, we characterize under what circumstances a voting system is “contestable” or “defensible.” Voting systems must be contestable and defensible in order to be meaningfully audited, and unfortunately BMDs are neither contestable nor defensible. Hand-marked paper ballots, counted by an optical-scan voting machine, are both contestable and defensible.

Ballot-Marking devices (BMDs) cannot assure the will of the voters

by Andrew W. Appel, Richard A. DeMillo, and Philip B. Stark

Abstract:

Computers, including all modern voting systems, can be hacked and misprogrammed. The scale and complexity of U.S. elections may require the use of computers to count ballots, but election integrity requires a paper-ballot voting system in which, regardless of how they are initially counted, ballots can be recounted by hand to check whether election outcomes have been altered by buggy or hacked software. Furthermore, secure voting systems must be able to recover from any errors that might have occurred.

However, paper ballots provide no assurance unless they accurately record the vote as the voter expresses it. Voters can express their intent by hand-marking a ballot with a pen, or using a computer called a ballot-marking device (BMD), which generally has a touchscreen and assistive interfaces. Voters can make mistakes in expressing their intent in either technology, but only the BMD is also subject to systematic error from computer hacking or bugs in the process of recording the vote on paper, after the voter has expressed it. A hacked BMD can print a vote on the paper ballot that differs from what the voter expressed, or can omit a vote that the voter expressed.

It is not easy to check whether BMD output accurately reflects how one voted in every contest. Research shows that most voters do not review paper ballots printed by BMDs, even when clearly instructed to check for errors. Furthermore, most voters who do review their ballots do not check carefully enough to notice errors that would change how their votes were counted. Finally, voters who detect BMD errors before casting their ballots, can correct only their own ballots, not systematic errors, bugs, or hacking. There is no action that a voter can take to demonstrate to election officials that a BMD altered their expressed votes, and thus no way voters can help deter, detect, contain, and correct computer hacking in elections. That is, not only is it inappropriate to rely on voters to check whether BMDs alter expressed votes, it doesn’t work.

Risk-limiting audits of a trustworthy paper trail can check whether errors in tabulating the votes as recorded altered election outcomes, but there is no way to check whether errors in how BMDs record expressed votes altered election out- comes. The outcomes of elections conducted on current BMDs therefore cannot be confirmed by audits. This paper identifies two properties of voting systems, contestability and defensibility, that are necessary conditions for any audit to confirm election outcomes. No commercially available EAC-certified BMD is contestable or defensible.

To reduce the risk that computers undetectably alter election results by printing erroneous votes on the official paper audit trail, the use of BMDs should be limited to voters who require assistive technology to vote independently.