secure voting

School of Engineering and Applied SciencesHarvard University

Voters, Computers, and Trust: Designing Verifiable Elections

Stuart M. ShieberBen Adida

Greg MorrisettCenter for Research on Computation and Society

October 18, 2008

Secure Voting

• Voting is particularly challenging:requires secrecy and public auditability.

• Computer science enablesqualitatively novel solutions.

• Cryptography can reconcileseemingly contradictory requirements.

"That's for me and a button to know."

Joe, the plumber.

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“When I finally sawthe results of our tests,

I thought I was going to throw up.”

Sec. of State, Ohio, last week.

Fashionable Voting

http://www.cs.uiowa.edu/~jones/voting/pictures/9

Fashionable Voting

http://www.cs.uiowa.edu/~jones/voting/pictures/9

Fashionable Voting

http://www.cs.uiowa.edu/~jones/voting/pictures/9

Fashionable Voting

http://www.cs.uiowa.edu/~jones/voting/pictures/9

Fashionable Voting

http://www.cs.uiowa.edu/~jones/voting/pictures/9

Fashionable Voting

http://www.cs.uiowa.edu/~jones/voting/pictures/9

Fashionable Voting

http://www.cs.uiowa.edu/~jones/voting/pictures/9

Fashionable Voting

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Voting is a fundamentally difficult problem.

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1 person, 1 vote

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Enforced Privacyto ensure each voter

votes in his/herown interest

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http://www.cs.uiowa.edu/~jones/voting/pictures/ 14

http://www.cs.uiowa.edu/~jones/voting/pictures/

1892 - Australian Ballot

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The Ballot Handoff

Alice the Voter

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McCain

The Ballot Handoff

Alice the Voter

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McCain

The Ballot Handoff

Alice the Voter

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McCain

The Ballot Handoff

Alice the Voter

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McCain

The Ballot Handoff

Alice the Voter

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McCain

ObamaObamaObama

McCainMcCain

McCain

The Ballot Handoff

Alice the Voter

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McCain

ObamaObamaObama

McCainMcCain

Black Box

McCain

Chain of Custody

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Chain of Custody

Vendor

/*

* source

* code

*/

if (...

1

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Chain of Custody

VotingMachine

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Vendor

/*

* source

* code

*/

if (...

1

19

Chain of Custody

VotingMachine

2

Vendor

/*

* source

* code

*/

if (...

1

Polling Location

3

19

Chain of Custody

VotingMachine

2

Vendor

/*

* source

* code

*/

if (...

1

Polling Location

3

4

Alice

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Chain of Custody

VotingMachine

2

Vendor

/*

* source

* code

*/

if (...

1

Polling Location

3

4

Alice

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Chain of Custody

VotingMachine

2

Vendor

/*

* source

* code

*/

if (...

1

Polling Location

3

Ballot Box Collection

5

4

Alice

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Chain of Custody

VotingMachine

2

Vendor

/*

* source

* code

*/

if (...

1

Polling Location

3

Ballot Box Collection

5

Results

.....6

4

Alice

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Chain of Custody

VotingMachine

2

Vendor

/*

* source

* code

*/

if (...

1

Polling Location

3

Ballot Box Collection

5

Results

.....6

4

Alice

Black Box19

Computers have only obscured the process.

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Computers have only obscured the process.

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What aboutcomputer science?

Cryptographysolving problems that initially

appear to have conflicting requirements.

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Public-Key Encryption

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Customer

Public-Key Encryption

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Customer

public key

Public-Key Encryption

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Customer

public key

enc(cc number)

Bulletin Board

Public Ballots

Bob:McCain

Carol:Obama

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Bulletin Board

Public Ballots

Bob:McCain

Carol:Obama

Alice

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Bulletin Board

Public Ballots

Alice:Obama

Bob:McCain

Carol:Obama

Alice

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Bulletin Board

Public Ballots

Alice:Obama

Bob:McCain

Carol:Obama

Tally

Obama....2McCain....1

Alice

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Encrypted Public BallotsBulletin Board

Alice:Rice

Bob:Clinton

Carol:Rice

Tally

Obama....2McCain....1

Alice

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Encrypted Public BallotsBulletin Board

Alice:Rice

Bob:Clinton

Carol:Rice

Tally

Obama....2McCain....1

Alice

Alice verifies her vote

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Encrypted Public BallotsBulletin Board

Alice:Rice

Bob:Clinton

Carol:Rice

Tally

Obama....2McCain....1

Alice

Alice verifies her vote Everyone verifies the tally

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How can we verify operations on

encrypted data?

Mathematical Proofs.

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Zero-Knowledge Proof

Vote For:

Obama

President:

Mickey MousePresident:

Mickey MousePresident:

Mickey MousePresident:

Mickey MousePresident:

Mickey MousePresident:

Mickey MouseVote For: Obama

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Zero-Knowledge Proof

Vote For:

Obama

President:

Mickey MousePresident:

Mickey MousePresident:

Mickey MousePresident:

Mickey MousePresident:

Mickey MousePresident:

Mickey MouseVote For: Obama

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Zero-Knowledge Proof

This last envelope likely contains “Obama”

Vote For:

Obama

President:

Mickey MousePresident:

Mickey MousePresident:

Mickey MousePresident:

Mickey MousePresident:

Mickey MousePresident:

Mickey MouseVote For: Obama

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Zero-Knowledge Proof

Open envelopes don’t proveanything after the fact.

President:

Mickey MousePresident:

Mickey MousePresident:

Mickey MousePresident:

Mickey MousePresident:

Mickey MousePresident:

Mickey MouseVote For: Obama

President:

Mickey MousePresident:

Mickey MousePresident:

Mickey MousePresident:

Mickey MousePresident:

Mickey MousePresident:

Mickey MouseVote For:

Paul

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McCain