Voters, Computers, and Trust:
Designing Verifiable Elections
Stuart M. Shieber
Ben Adida
Greg Morrisett
Center for Research on Computation and Society
October 18, 2008
School of Engineering and Applied Sciences
Harvard University

Secure Voting

• Voting is particularly challenging:
requires secrecy and public auditability.
• Computer science enables
qualitatively novel solutions.
• Cryptography can reconcile
seemingly contradictory requirements.

\"That's for me and a
button to know.\"
Joe, the plumber.

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“When I finally saw
the 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

Enforced Privacy
to ensure each voter
votes in his/her
own interest
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http://www.cs.uiowa.edu/~jones/voting/pictures/ 14

1892 - Australian Ballot
http://www.cs.uiowa.edu/~jones/voting/pictures/ 15

The Ballot Handoff
McCain
Alice the Voter
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The Ballot Handoff
McCain
Alice the Voter
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The Ballot Handoff
McCain
Alice the Voter
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The Ballot Handoff
McCain
Alice the Voter
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The Ballot Handoff
McCain Obama
Obama
Obama
McCain
McCain
McCain
Alice the Voter
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The Ballot Handoff
McCain Obama
Obama
Obama
McCain
McCain
McCain
Alice the Voter Black Box
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Chain of Custody
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Chain of Custody
1
/*
* source
* code
*/
if (...
Vendor
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Chain of Custody
1
/*
* source
* code
Voting */
2
Machine
if (...
Vendor
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Chain of Custody
1
/*
* source
* code
Polling Voting */
3 2
Location Machine
if (...
Vendor
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Chain of Custody
1
/*
* source
* code
Polling Voting */
3 2
Location Machine
if (...
Vendor
4
Alice
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Chain of Custody
1
/*
* source
* code
Polling Voting */
3 2
Location Machine
if (...
Vendor
4
Alice
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Chain of Custody
1
/*
* source
* code
Polling Voting */
3 2
Location Machine
if (...
Vendor
4
Alice
5
Ballot Box Collection
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Chain of Custody
1
/*
* source
* code
Polling Voting */
3 2
Location Machine
if (...
Vendor
4
Alice
Results
5 6 .....
Ballot Box Collection
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Chain of Custody
1
/*
* source
* code
Polling Voting */
3 2
Location Machine
if (...
Vendor
4
Alice
Results
5 6 .....
Ballot Box Collection
Black Box
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Computers have only
obscured the process.
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Computers have only
obscured the process.
What about
computer science?
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Cryptography
solving problems that initially
appear to have conflicting
requirements.
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Public-Key Encryption
Customer
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Public-Key Encryption
public key
Customer
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Public-Key Encryption
public key
enc(cc number)
Customer
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Public Ballots
Bulletin Board
Bob:
McCain
Carol:
Obama
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Public Ballots
Bulletin Board
Bob:
McCain
Carol:
Obama
Alice
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Public Ballots
Bulletin Board
Alice: Bob:
Obama McCain
Carol:
Obama
Alice
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Public Ballots
Bulletin Board
Alice: Bob:
Obama McCain
Carol:
Obama
Tally
Obama....2
McCain....1
Alice
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Encrypted Public Ballots
Bulletin Board
Alice: Bob:
Rice Clinton
Carol:
Rice
Tally
Obama....2
McCain....1
Alice
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Encrypted Public Ballots
Bulletin Board
Alice: Bob:
Rice Clinton
Carol:
Ali Rice
ce
ver Tally
ifies
he
rv Obama....2
ote
McCain....1
Alice
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Encrypted Public Ballots
Bulletin Board
Alice: Bob:
Rice Clinton
Carol:
lly
Ali ta
Rice
ce e
thTally
ver es
rifi
ifies
e ve
he n
ryo
rv ve Obama....2
E
ote
McCain....1
Alice
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How can we verify
operations on
encrypted data?
Mathematical Proofs.
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Zero-Knowledge Proof
President:
President:
Mickey Mouse
President:
Mickey Mouse
President:
Mickey Mouse
President:
Mickey Mouse
President:
Mickey Mouse
Vote For:
Mickey Mouse
Obama
Vote For:
Obama
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Zero-Knowledge Proof
President:
President:
Mickey Mouse
President:
Mickey Mouse
President:
Mickey Mouse
President:
Mickey Mouse
President:
Mickey Mouse
Vote For:
Mickey Mouse
Obama
Vote For:
Obama
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Zero-Knowledge Proof
President:
President:
Mickey Mouse
President:
Mickey Mouse
President:
Mickey Mouse
President:
Mickey Mouse
President:
Mickey Mouse
Vote For:
Mickey Mouse
Obama
Vote For:
Obama
This last envelope
likely contains “Obama”
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Zero-Knowledge Proof
President: President:
President: President:
Mickey Mouse Mickey Mouse
President: President:
Mickey Mouse Mickey Mouse
President: President:
Mickey Mouse Mickey Mouse
President: President:
Mickey Mouse Mickey Mouse
President: President:
Mickey Mouse Mickey Mouse
Vote For: Vote For:
Mickey Mouse
Mickey Mouse
McCain
Paul
Obama
Open envelopes don’t prove
anything after the fact.
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