Threat Model Who is the attacker? ➡ administration officials, candidates, poll workers, even voters What is the Benefit? How will the attacks be carried out? ➡ corruption of input, ballot box, transport, tallying ➡ coercion of voters Where will the attacks be hidden? ➡ honest mistakes: randomly distributed in the process ➡ malicious intent: hiding where you least defend 29
So what can we do? 30
Wooten got the news from his wife, Roxanne, who went to City Hall on Wednesday to see the election results. “She saw my name with zero votes by it. She came home and asked me if I had voted for myself or not. I told her I did,” said Wooten, owner of local bar. 31
Open audit elections Cryptography provides more than confidentiality. Cryptography can provide both verifiability and ballot secrecy Anyone can audit! 32
Public Ballots Bulletin Board Bridget : Sweet Carol : Salty 33
Public Ballots Bulletin Board Bridget : Sweet Carol : Salty Alice 33
Public Ballots Bulletin Board Alice : Bridget : Sweet Sweet Carol : Salty Alice 33
Public Ballots Bulletin Board Alice : Bridget : Sweet Sweet Carol : Salty Tally Sweet.......2 Salty..........1 Alice 33
Encrypted Public Ballots Bulletin Board Alice : Bridget : Rice Clinton Carol : Rice Tally Sweet.......2 Salty..........1 Alice 34
Encrypted Public Ballots Bulletin Board Alice : Bridget : Rice Clinton Carol : Alice verifies her vote Rice Tally Sweet.......2 Salty..........1 Alice 34
Encrypted Public Ballots Bulletin Board Alice : Bridget : Rice Clinton Carol : Everyone verifies the tally Alice verifies her vote Rice Tally Sweet.......2 Salty..........1 Alice 34
Public-Key Encryption 35
Public-Key Encryption Keypair consists of a public key and a secret key . pk sk 35
Public-Key Encryption Keypair consists of a public key and a secret key . pk sk Enc pk "Salty" 8b5637 35
Public-Key Encryption Keypair consists of a public key and a secret key . pk sk Enc pk "Salty" 8b5637 Enc pk "Sweet" c5de34 35
Public-Key Encryption Keypair consists of a public key and a secret key . pk sk Enc pk "Salty" 8b5637 Enc pk "Sweet" c5de34 Enc pk "Salty" a4b395 35
Threshold Decryption Secret key is shared amongst multiple parties: all (or at least a quorum) need to cooperate to decrypt. 8b5637 36
Threshold Decryption Secret key is shared amongst multiple parties: all (or at least a quorum) need to cooperate to decrypt. Dec sk 1 b739cb 8b5637 36
Threshold Decryption Secret key is shared amongst multiple parties: all (or at least a quorum) need to cooperate to decrypt. Dec sk 1 b739cb Dec sk 2 261ad7 8b5637 36
Threshold Decryption Secret key is shared amongst multiple parties: all (or at least a quorum) need to cooperate to decrypt. Dec sk 1 b739cb Dec sk 2 261ad7 8b5637 Dec sk 3 7231bc 36
Threshold Decryption Secret key is shared amongst multiple parties: all (or at least a quorum) need to cooperate to decrypt. Dec sk 1 b739cb Dec sk 2 261ad7 8b5637 Dec sk 3 7231bc Dec sk 4 8239ba 36
Threshold Decryption Secret key is shared amongst multiple parties: all (or at least a quorum) need to cooperate to decrypt. Dec sk 1 b739cb Dec sk 2 261ad7 8b5637 "Salty" Dec sk 3 7231bc Dec sk 4 8239ba 36
Tallying Method I: Homomorphic Tabulation [Benaloh’87] Enc ( m 1 ) × Enc ( m 2 ) = Enc ( m 1 + m 2 ) 37
Tallying Method I: Homomorphic Tabulation [Benaloh’87] Enc ( m 1 ) × Enc ( m 2 ) = Enc ( m 1 + m 2 ) Yes = Enc (1) No = Enc (0) 37
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