UMBC Cyber Defense Lab

BVOT: Self-Tallying Boardroom Voting with Oblivious Transfer

Farid Javani, CSEE, UMBC

12:00–1:00pm, Friday, 6 November 2020

http://umbc.webex.com/meet/sherman

(Joint work with Alan T. Sherman)

A boardroom election is an election with a small number of voters carried out with public communications. We present BVOT, a self-tallying boardroom voting protocol with ballot secrecy, fairness (no tally information is available before the polls close), and dispute-freeness (voters can observe that all voters correctly followed the protocol).

BVOT works by using a multiparty threshold homomorphic encryption system in which each candidate is associated with a masked unique prime. Each voter engages in an oblivious transfer with an untrusted distributor: the voter selects the index of a prime associated with a candidate and receives the selected prime in a masked form. The voter then casts their vote by encrypting their masked prime and broadcasting it to everyone. The distributor does not learn the voter’s choice, and no one learns the mapping between primes and candidates until the audit phase. By hiding the mapping between primes and candidates, BVOT provides voters with insufficient information to carry out effective cheating. The threshold feature prevents anyone from computing any partial tally—until everyone has voted. Multiplying all votes, their decryption shares, and the unmasking factor yields a product of the primes each raised to the number of votes received.

In contrast to some existing boardroom voting protocols, BVOT does not rely on any zero-knowledge proof; instead, it uses oblivious transfer to assure ballot secrecy and correct vote casting. Also, BVOT can handle multiple candidates in one election. BVOT prevents cheating by hiding crucial information: an attempt to increase the tally of one candidate might increase the tally of another candidate. After all votes are cast, any party can tally the votes.

Farid Javani is a Ph.D. candidate in computer science at UMBC, working with Alan Sherman. His research interests include algorithms, security, applied cryptography, and distributed systems. He is the manager of the Enterprise Architecture team at CCC Information Services in Chicago. email: *protected email*

Host: Alan T. Sherman, *protected email* Support for this event was provided in part by the National Science Foundation under SFS grant DGE-1753681. The UMBC Cyber Defense Lab meets biweekly Fridays 12-1:00 pm. All meetings are open to the public. Upcoming CDL Meetings: Oct. 30, Jonathan Katz (UMCP), [possibly on secure distributed computation]; Nov. 13, TBA, [possibly: David R Imbordino (NSA), Security of the 2020 presidential election]; and Dec. 11, TBA, [possibly: Peter A. H. Peterson (Univ. of Minnesota Duluth), Adversarial Thinking]

UMBC Cyber Defense Lab

BVOT: Self-Tallying Boardroom Voting with Oblivious Transfer

Farid Javani, CSEE, UMBC

12:00–1:00pm, Friday, 6 November 2020

http://umbc.webex.com/meet/sherman

(Joint work with Alan T. Sherman)

A boardroom election is an election with a small number of voters carried out with public communications. We present BVOT, a self-tallying boardroom voting protocol with ballot secrecy, fairness (no tally information is available before the polls close), and dispute-freeness (voters can observe that all voters correctly followed the protocol).

BVOT works by using a multiparty threshold homomorphic encryption system in which each candidate is associated with a masked unique prime. Each voter engages in an oblivious transfer with an untrusted distributor: the voter selects the index of a prime associated with a candidate and receives the selected prime in a masked form. The voter then casts their vote by encrypting their masked prime and broadcasting it to everyone. The distributor does not learn the voter’s choice, and no one learns the mapping between primes and candidates until the audit phase. By hiding the mapping between primes and candidates, BVOT provides voters with insufficient information to carry out effective cheating. The threshold feature prevents anyone from computing any partial tally—until everyone has voted. Multiplying all votes, their decryption shares, and the unmasking factor yields a product of the primes each raised to the number of votes received.

In contrast to some existing boardroom voting protocols, BVOT does not rely on any zero-knowledge proof; instead, it uses oblivious transfer to assure ballot secrecy and correct vote casting. Also, BVOT can handle multiple candidates in one election. BVOT prevents cheating by hiding crucial information: an attempt to increase the tally of one candidate might increase the tally of another candidate. After all votes are cast, any party can tally the votes.

Farid Javani is a Ph.D. candidate in computer science at UMBC, working with Alan Sherman. His research interests include algorithms, security, applied cryptography, and distributed systems. He is the manager of the Enterprise Architecture team at CCC Information Services in Chicago. email: *protected email*

Host: Alan T. Sherman, *protected email* Support for this event was provided in part by the National Science Foundation under SFS grant DGE-1753681. The UMBC Cyber Defense Lab meets biweekly Fridays 12-1:00 pm. All meetings are open to the public. Upcoming CDL Meetings: Oct. 30, Jonathan Katz (UMCP), [possibly on secure distributed computation]; Nov. 13, TBA, [possibly: David R Imbordino (NSA), Security of the 2020 presidential election]; and Dec. 11, TBA, [possibly: Peter A. H. Peterson (Univ. of Minnesota Duluth), Adversarial Thinking]

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