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The Denver Mobile Voting Pilot: A Report

  • 100 % of survey respondents said that of all the methods of voting, they preferred voting on their smartphone.


This report describes the following: the post-election audit process of the Denver Municipal election mobile voting pilots conducted by the National Cybersecurity Center. An overview of how informed military voters, their families and civilians residing overseas received, marked and returned their ballots from their iOS and Android smartphones from 36 countries.

The Problem: How Can Denver Provide a Secure and Convenient Way to Vote for Military and Overseas Citizens?

In preparing for its 2019 municipal election, the City and County of Denver needed to identify a solution to the unique obstacles faced by overseas citizens and active-duty military personnel and their families. Those obstacles range from poor mail delivery to lack of access to regular mail. Because of these unique challenges, state and federal laws, including the Uniformed and Overseas Citizen Absentee Voting Act (UOCAVA), grant special voting privileges to these voters, including an electronic method of voting.

Denver had been offering a web-based platform through which qualified voters can access and mark their ballot over several election cycles. Because UOCAVA voters are required to sign an affidavit with their voted ballot, they needed to print, sign, and then scan the affidavit in order to return their ballot electronically. Since most voters in these circumstances are unlikely to have access to a printer and scanner, these requirements presented additional hurdles, impeding their ability to vote.

Assuming voters were able to successfully print, sign, and scan their affidavits, they then needed to securely transmit their voted ballot and signed affidavit back to the Denver Elections office. Because Denver does not have access to the secure file transfer site used by the Colorado Secretary of State for municipal elections, email became the only electronic method of return. UOCAVA voters were forced to email PDF attachments containing their voted ballot and signed affidavit. This is one of the most insecure return methods available and offered voters and Denver Elections no assurance that the email was not tampered with and that the ballot was received as marked.

In short, before 2019 Denver UOCAVA voters had very limited options when it came to voting – all of which were highly insecure and inconvenient.

The Solution: A Blockchain-Based Mobile Voting Application

Denver determined that a blockchain-based mobile voting application could offer a more secure method of returning cast ballots, compared to email and even the secure file transfer site. The election office sought a solution that could utilize the convenience of a mobile device, while enhancing the security and transparency of the electronic voting experience for UOCAVA voters. Mobile devices increase the convenience of voting electronically by offering a single tool by which voters could meet all of the requirements to vote without the need for printers, scanners, or other equipment. Voters can receive and mark their ballot and sign the required affidavit all on their device. By using a mobile application, Denver could utilize the device’s security features, including hardware-based encryption and biometrics, to ensure that only the eligible voter can access and vote his/her ballot. Casting and recording votes over blockchain ensured that mobile votes were immutable and tamper-proof once recorded. The blockchain-based solution also offered a transparent method through which voters could verify their ballot was recorded as intended and independent auditors could assess whether the election outcome was correct.

The Pilot: Partnering with Voatz, Tusk Philanthropies, and the National Cybersecurity Center

The Denver Elections Division partnered with Tusk Philanthropies and the National Cybersecurity Center to conduct a security audit and review of several vendors offering blockchain-based mobile voting applications. After public demonstrations with experts in blockchain, elections, and voting rights, Denver selected the Voatz application for use in both the municipal general and run-off elections.

When the facial recognition portion was finished, voters were then able to access their ballot, mark their selections and proceed to sign the affidavit directly on the phone’s touchscreen, effectively eliminating the need for any secondary technology. Voters then use their biometric fingerprint as registered in the phone’s internal security to cast the ballot. Once a voter submits the ballot, the voter receives a digital receipt showing his/her ballot selections. If a voter noticed something amiss, he or she could immediately cancel the vote and receive a new ballot through traditional methods.

The Denver Elections office simultaneously received an anonymized copy of the digital receipt as well as an email containing the signed affidavit. The UOCAVA processing team proceeded with signature verification following the same guidelines used for all voters. The cast ballots were housed in a separate Voatz dashboard, only to be accessed in bulk when preparing to tabulate the election results. The dashboard required two designated users to sign-in simultaneously to download and print the ballots directly onto ballot stock for scanning and tabulation with all other ballots cast.

Transparency and Auditability 

Following the election, Denver also piloted a third-party audit tool to make the votes cast through the blockchain fully transparent and auditable. This digital bulletin board was made available to any interested party who wanted to participate, including election observers and experts in election administration and blockchain technology. The tool enabled auditors to verify each of the following steps:

  • Votes recorded on the blockchain from the voter’s device. 
  • Votes recorded on ballot images extracted from the blockchain.
  • Votes recorded in the tabulation system from the cast vote record. 

The data was verified against the anonymized voter-verified digital receipt. Eighteen independent auditors participated in the initial audit following the Municipal General Election. All auditors confirmed the accuracy of the cast vote record against the voter-verified digital receipts.

Results and Findings

Overall, the pilots in the Municipal General and Run-Off Elections were successful, and the Denver Elections Division was recognized with the Democracy Award from the National Association of Election Officials. Turnout among UOCAVA voters more than doubled the previous municipal election, suggesting that the more convenient voting method may have encouraged more voters to participate. In surveys of voters who participated in the pilot, they unanimously stated they preferred to vote through the mobile app over any other method of voting in the future. And the third-party audit demonstrated successfully that the votes cast over the blockchain were recorded and tabulated accurately.

In the future, this technology holds the promise of making voting easier not only for UOCAVA voters, but also voters with disabilities. And the transparency of the system holds the promise of offering an end-to-end verifiable election system through which anyone can verify the election outcome is correct – a critical step forward in protecting and preserving our democratic process.