2005-02-22 1

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UNIVERSITY

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Sakurai Lab. Kyushu University

Dr-course HER, Yong-Sork

E-voting VS. E-auction

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What is a Electronic-Voting ?

• To prevent the losses by the conventional voting system

• Using Network and cryptography techniques

• Automatic and fast voting procedure

• Untill it is realized the home–voting, Convenient place-voting….

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Requirements for E-voting system

Completeness : All valid votes are counted correctly, if all participants are honestRobustness : Dishonest voters, other participants or outsiders can not disturb of disrupt an electionPrivacy : The votes are cast anonymously

Unreuability : Every voter can vote only once.

Eligibility : Only legitmate voters can vote

Fairness : A voter casts his vote independently and is not influenced

Universal Verifiability : anyone can verify a correctness of election.

Receipt-freeness: A voter can not prove to a coercer, how he has voted

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• Okayama ( 岡山 )on 23, June (2002)

- Niimi( 新見 ) : A mayoral and a municipal election

• Touch panel method like ATM (Automated-teller Machine) of BANK.

• General voter

• Absentee voter

The First E-voting in Japan

2005-02-22 5

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Authentication

Receive IC-cardInput the IC card in voting terminal

VotingStore the contents of voter

Okayama’s e-voting

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Analysis of Japan‘s e-voting

ItemsThe existed voting1994 (Paper-voting)

The electronic Voting2002

Voting officer(43-voting place)

180-person 178-person

Counting officer 85-person 58-person

Admission member（入会人 )

13-person 13-person

Counting time-Major

-Councilman3 hours

4 hours 25 minutes25 minutes25 minutes

Invalid ballots-Major

-Councilman242214

00

Voting ratio 92.06 % 86.82 %

Election costs \11,630,000 \16,460,000

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Analysis of Japan ‘s e-voting (Cont.)

CandidateGroup

The ratio of votes obtained

E-voting< General voter>

Existing voting<Absentee voter>

Candidate 1 78.4 % 69.6 %

Candidate 2 9 % 11.5 %

Candidate 3 5 %

Candidate 4

Total 100%

<14,966 persons> 100 %

<1719 persons>

13.3 %

11.5 % 5.6 %

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E-voting ServerVoter

SSL

DB- Registration step- Voting step- Counting step

Example of E-voting system (1)

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UNIVERSITY

SAKURAI

LABORATORY

Voting system(WIN95, 486-II)

Server(Linux 2.x, P-75Mhz)

Firewall(FWTK)

SSL SSL

(Stronghold, UK)

Encryption/Decryption ( PGP)

Voting program(Perl- language)

VoteCount1

The example of voting contents

(Before be transmitted)

Transmitting of encryption

The Implement of E-voting System (1)

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Voting center

Absentee voter

Absentee Center

①Register a

n absentee

②Send the public

-key

③Send the public-key

Bulletin Board

④Choose candidate and double encryption

⑤Send the contents of absentee

⑥Decryptand computethe voting results

⑦ Sendthe computedVoting results

⑧ Compute the voting results

⑨compare with the results of and⑦ ⑧

E-voting system for an absentee voter　　　 => Ballot-Cancellation Scheme

2005-02-22 11

KYUSHU

UNIVERSITY

SAKURAI

LABORATORY

What is a auction ?

Not a fixed Price A kind of trade for special goods In real world, a various type auctions have been enforced for decision of price

2005-02-22 12

KYUSHU

UNIVERSITY

SAKURAI

LABORATORY

E-auction

Bidder . . . . .

$10 $9 $11$12

Encryption Key

$ Bidding price

Recently, e-auction using Cryptographic Techniques and Network have been proposed.

A B N-1 N

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A first-price sealed-bid auction

A second-price sealed-bid auction

M+1st –price auctionMultiple units of a single item are auctioned. The M highest bidders win and pay (M+1)st highest bid

. . .

Types of an E-auction

The winner is the highest bidding price, he should pay his own bidding price.

The winner is the highest bidding price, he should pay the second-price.

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Requirements

Privacy of bid : No bid is revealed to anyone except the winner and the winning bid Proof of winner : Everyone can verify the winner and the winning price which are decided correctly Non-repudiation : The winner cannot repudiate his/her own bidding at the winning price Accountability of bidder : Any auctioneer can verify that bidders follow a protocol to cast their bids. 　 Bid Security　　 Nobody can forge (falsify) and tap a bid。 Robustness 　　 Even if a bidder sends an invalid bid, the auction process is unaffected.

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O.K

To receive the money, a bidder should prove to coercer (or buyer) how he bided. Please, make a bid

with low biding price

Receipt-Free Scheme in E-auction

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• <AS02> M.Abe, K.Suzuki “ Receipt-Free Sealed-Bid Auction”, ISC2002, LNCS 2002

• <CLK03> X.Chen, B.C.Lee, K.J.Kim “ Receipt-free Electronic Auction Schemes Using Homomorphic Encryption”, ICISC2003,

Related works

Scheme

[AS02] [CLK03]

WinnerLosing bidders

WinnerLosing bidders

Receipt-free scheme

No Yes Yes Yes

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LABORATORY

Example of e-auction (1)

Auctioneer : An auctioneer decides the winning price and publishes it. Multi-Auction issuer Each auction issuer mixes the encrypted bidding price. The last auction issuer manages Pseudo ID of each bidder.Bidder : A bidder offers a bid only one time by an auction rule Bulletin Board Everyone can see the content of BB and can not erase/modify it.

Participants

…We suppose that the auctioneer does not collude with last-auction issuer

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• Notation

A secret key and a public key of an auctioneer

A secret key and a public key of an auctioneer for designated verifier re-encryption proof

A secret key and a public key of an auction issuer

A secret key and a public key of a bidder

Random numbers

A generator

AA yx ,

uu yS ,

II yx ,

BB yx ,

qp,

'gpgg k mod)( '

Example of e-auction (1)

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Procedures 1. Registration Stage

Bidder Last -Auction issuer

Real ID

Pseudo ID Generator

Pseudo ID )( 2qiIDZP

Anonymous secret channel

Example of e-auction (1)

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2. Bidding stage

Bidder

Public key Iy

Random number )( 2qb Zr

bIDIbID rPxrPI ggyP 0

Bidding ID Vector

Bidder

Public key Ay

Random encryption factor 210 ),( qZkkk

)],();,[(

)],(),,[(1100

11000

kkA

kkAi gygyb

yxyxC

　 　

Bidding Vector

Last -Auction Issuer

Auctioneer

Example of e-auction (1)

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LABORATORY

3. Mixing stage

1 -AI2 -AI last -AI

.

.

.

.

.

....

.

.

.

1C 2C 1nC-Group -Group -Group

Example of e-auction (1)

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VerifierProver

22,1 ,, qZtrkk

'222

'1211

'1

'1

'0

'0 ),,,,,,,,,(

)],(),,[(

)],)(,[(

2211

aakU

aaakT

yxyxFdcbaHS

ygF

gygy

dcba

tu

r

kkkk

),,,,( UTStr

),,,,

,,,,('1

'1

'1

'0

'1

'1

'0

'0

yxyxyg

ygxyygxyStu

r

UUTT

　　　　　 　

　　　

Compute

Accept the proof if

Designated-Verifier Re-encryption proof for Universal Re-encryption

Example of e-auction (1)

2005-02-22 23

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VerifierProver

qZ

gbga ,),( ba

crc bvyaug ,

Compute

Accept the proof if

qZc

cCompute

IDcPr r

Proof of Knowledge of Pseudo ID

Example of e-auction (1)

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LABORATORY

4. Opening Stage

AuctioneerRecover 0P

AA xkkx yxPyx )/()/('0

'0

110'1

'1

ixkk

ix byxbyx AA )/()/(

'0

'0

00'0

'0

Compute the bidding price

Bulletin Board

Example of e-auction (1)

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5. Trading Stage

WinnerProof of Bidding ID vector

Last -Auction issuer

Recover

Pseudo ID of the winner

Example of e-auction (1)

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Future works

• Compare E-voting system with E-auction system

• Extended Receipt-free Scheme for E-auction system

• Develop E-voting System for an absentee