Electronic Voting in the Standard Model
SemesterarbeitSS03
Thomas Briner Betreuung: Martin Hirt
Vote v
Voter Authority
Bulletin Board
SKA
Homomorphic Encryption
E(v1) ⊕ E(v
2) = E(v
1+ v
2)
Bulletin Board
SKA
Bulletin Board
SKA
Bulletin Board
SKA
randomness
Bulletin Board
1,...,T
N)
Bulletin Board
1,...,T
N)
e = E(v,α)
homomorphicencryption
vblinding
ē
SKA
ē ē
ē ē
homomorphicencryption
v
blinding
ē
0 1 0 0 0 0 0
Cand 1 Cand LCand 2 .....
e E(0) E(1) E(0) E(0) E(0) E(0) E(0)
E(0) E(0) E(0) E(0) E(0) E(1) E(0)
homomorphic encryptionv
blinding with correct key
ē
e
casted vote
encrypted and blinded voteas sent in ballot
homomorphic encryptionv
blinding with correct key
ē
e
v'
e'
casted vote
homomorphic encryption
blinding with fake key
claimed vote
encrypted and blinded voteas sent in ballot
ē
casted voteclaimed vote
ballot = (voter ID,vote ID,encrypted and permuted vote ,ēvalidity proof,tag,signature )
encrypted permuted vote ē
tag
T
key = ax + b
P
permutation π
encrypted permuted vote ē
tag
T'
key = ax + b
P
permutation π
permutation π'
P
tag
T
key = ax + b
encrypted permuted vote , permutation ē π
tag
T
encrypted permuted vote , permutation ē π '
tag
T
claimed keys
Possible States for each Voter
empty: No correctly signed ballot invalid: One or more correctly signed but
only invalid ones valid: Exactly one correctly signed and valid double: More than one correctly signed and
valid ones
List of Accusations
The Voter's View
� Receives letter with a permutation and a key
� Chooses his vote
� Encrypts his vote
� Permutes the encrypted vote
� Sends it to at least one honest authority
� Generates fake keys for each permutation he wants to claim
� “Proves” to the votebuyer that he has casted the desired vote
Properties of this Protocol
Privacy: Yes!Availability: Yes!Correctness: Not completely,
detection of irregularities but no prevention
Receipt-freeness:Yes!
E PK A
(v)
E PK A
(v)
Vielen Dank für die Aufmerksamkeit!
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