Privacy-Enhanced Event Scheduling -...

Faculty of Computer Science Institute of Systems Architecture, Chair of Privacy and Data Security

Privacy-Enhanced Event Scheduling

http://dudle.inf.tu-dresden.de

Benjamin.Kellermann@tu-dresden.de

D19E 04A8 8895 020A 8DF60092 3501 1A32 491A 3D9C

Berlin, December 29, 2009

PrimeLife is a research projectfunded by the European Commis-

sion's 7th Framework Programme

Event Scheduling

Benjamin Kellermann Privacy-Enhanced Event Scheduling slide 2 of 31

Privacy ProblemsDirect Inference

Will my husband vote for

the date of our

wedding anniversary?

Privacy ProblemsDirect Inference

Will my husband vote for

the date of our

wedding anniversary?

Privacy ProblemsIndirect Inference

The availability pattern of user bunny23 looks

suspiciously like the one of my employee John Doe!

Privacy ProblemsIndirect Inference

The availability pattern of user bunny23 looks

suspiciously like the one of my employee John Doe!

Table of Contents

Problem Statement

Scheme

Extensions

Evaluation

Conclusion and Outlook

GFDL Hajotthu

Requirements

• Untrusted Server

• Privacy

• Veri�ability

• Low Communication

Complexity

• Low Computational

Complexity

Requirements

• Privacy

• Veri�ability

Complexity

Requirements

• Privacy

• Veri�ability

Complexity

E-Voting vs. Event Scheduling

Candidate #1

Candidate #2 8

Candidate #10

Candidate #1

Candidate #2 8

Candidate #10

Candidate #1

Candidate #2 8

Candidate #10

Candidate #1

Candidate #2 8

Candidate #10

Candidate #1

Candidate #2 8

Candidate #10

Candidate #1

Candidate #2 8

Candidate #10

Candidate #1

Candidate #2 8

Candidate #10

scales

. . . Date

Yes 8 8

. . . Date

Yes 8 8

. . . Date

Yes 8 8

. . . Date

Yes 8 8

. . . Date

Yes 8 8

. . . Date

Yes 8 8

. . . Date

Yes 8 8

scales

one vote per column

Candidate #1

Candidate #2 8

Candidate #10

Candidate #1

Candidate #2 8

Candidate #10

Candidate #1

Candidate #2 8

Candidate #10

Candidate #1

Candidate #2 8

Candidate #10

Candidate #1

Candidate #2 8

Candidate #10

Candidate #1

Candidate #2 8

Candidate #10

Candidate #1

Candidate #2 8

Candidate #10

scales

. . . Date

Yes 8 8

. . . Date

Yes 8 8

. . . Date

Yes 8 8

. . . Date

Yes 8 8

. . . Date

Yes 8 8

. . . Date

Yes 8 8

. . . Date

Yes 8 8

scales

one vote per column

Candidate #1

Candidate #2 8

Candidate #10

Candidate #1

Candidate #2 8

Candidate #10

Candidate #1

Candidate #2 8

Candidate #10

Candidate #1

Candidate #2 8

Candidate #10

Candidate #1

Candidate #2 8

Candidate #10

Candidate #1

Candidate #2 8

Candidate #10

Candidate #1

Candidate #2 8

Candidate #10

scales

. . . Date

Yes 8 8

. . . Date

Yes 8 8

. . . Date

Yes 8 8

. . . Date

Yes 8 8

. . . Date

Yes 8 8

. . . Date

Yes 8 8

. . . Date

Yes 8 8

scales

one vote per column

Candidate #1

Candidate #2 8

Candidate #10

Candidate #1

Candidate #2 8

Candidate #10

Candidate #1

Candidate #2 8

Candidate #10

Candidate #1

Candidate #2 8

Candidate #10

Candidate #1

Candidate #2 8

Candidate #10

Candidate #1

Candidate #2 8

Candidate #10

Candidate #1

Candidate #2 8

Candidate #10

scales

. . . Date

Yes 8 8

. . . Date

Yes 8 8

. . . Date

Yes 8 8

. . . Date

Yes 8 8

. . . Date

Yes 8 8

. . . Date

Yes 8 8

. . . Date

Yes 8 8

scales

one vote per column

Scheme

Problem Statement

Scheme

Extensions

Evaluation

Superposed Sending

Alice Bob

ka,c k b,

+ ka,b

+ ka,c mb

− ka,b

+ kb,c

mc − ka,c − kb,c

+ ka,b + ka,c

− ka,b + kb,c

− ka,c − kb,c

D. Chaum, �The dining cryptographers problem: Unconditional sender and recipient untraceability,� Journal ofCryptology, vol. 1, no. 1, pp. 65�75, Jan. 1988

Superposed Sending

Alice Bob

ka,c k b,

+ ka,b

+ ka,c mb

− ka,b

+ kb,c

+ ka,b + ka,c

− ka,b + kb,c

− ka,c − kb,c

Superposed Sending

Alice Bob

ka,c k b,

+ ka,b

+ ka,c mb

− ka,b

+ kb,c

+ ka,b + ka,c

− ka,b + kb,c

− ka,c − kb,c

Superposed Sending

Alice Bob

ka,c k b,

+ ka,b + ka,c

− ka,b + kb,c

− ka,c − kb,c

+ ka,b + ka,c

− ka,b + kb,c

− ka,c − kb,c

Superposed Sending

Alice Bob

ka,c k b,

ma + ka,b + ka,c mb − ka,b + kb,c

+ ka,b + ka,c

− ka,b + kb,c

− ka,c − kb,c

Superposed Sending

Alice Bob

ka,c k b,

ma + ka,b + ka,c mb − ka,b + kb,c

ma + ka,b + ka,c+mb − ka,b + kb,c+mc − ka,c − kb,c

Superposed Sending

Alice Bob

ka,c k b,

+ ka,b + ka,c

− ka,b + kb,c

− ka,c − kb,c

ma + ka,b + ka,c+mb − ka,b + kb,c+mc − ka,c − kb,c

Superposed Sending

Alice Bob

ka,c k b,

+ ka,b + ka,c

− ka,b + kb,c

− ka,c − kb,c

+ ka,b

+ ka,c+mb

− ka,b

+ kb,c+mc − ka,c − kb,c

Superposed Sending

Alice Bob

ka,c k b,

+ ka,b + ka,c

− ka,b + kb,c

− ka,c − kb,c

+ ka,b

+ ka,c+mb

− ka,b + kb,c

+mc − ka,c

− kb,c

Superposed Sending

Alice Bob

ka,c k b,

+ ka,b + ka,c

− ka,b + kb,c

− ka,c − kb,c

+ ka,b + ka,c

− ka,b + kb,c

− ka,c − kb,c

Poll Initialization

Alice Bob Carol Server

T, PT, PT, P E-mail

noti�cation

T . . . time slots

P . . . voters

~ka,c ~kc,a

~ka,b ~kb,a

~kb,c ~kc,b

exchange~ki,j . . . key vector

~ka,b ~kb,a Alice Bob

~ka,b~ka,b

ka,b,t1

ka,b,t|T |

−~ka,b

−ka,b,t1

−ka,b,t|T |

Poll Initialization

T, PT, PT, P E-mail

noti�cation

T . . . time slots

P . . . voters

~ka,c ~kc,a

~ka,b ~kb,a

~kb,c ~kc,b

~ka,b~ka,b

ka,b,t1

ka,b,t|T |

−~ka,b

−ka,b,t1

−ka,b,t|T |

Poll Initialization

T, PT, PT, P E-mail

noti�cation

T . . . time slots

P . . . voters

~ka,c ~kc,a

~ka,b ~kb,a

~kb,c ~kc,b

~ka,b~ka,b

ka,b,t1

ka,b,t|T |

−~ka,b

−ka,b,t1

−ka,b,t|T |

Poll Initialization

T, PT, PT, P E-mail

noti�cation

T . . . time slots

P . . . voters

~ka,c ~kc,a

~ka,b ~kb,a

~kb,c ~kc,b

~ka,b~ka,b

ka,b,t1

ka,b,t|T |

−~ka,b

−ka,b,t1

−ka,b,t|T |

Poll Initialization

T, PT, PT, P E-mail

noti�cation

T . . . time slots

P . . . voters

~ka,c ~kc,a

~ka,b ~kb,a

~kb,c ~kc,b

~ka,b~ka,b

ka,b,t1

ka,b,t|T |

−~ka,b

−ka,b,t1

−ka,b,t|T |

Casting of Votes

T, PT, PT, P E-mail

noti�cation

T . . . time slots

P . . . voters

~ka,c ~kc,a

~ka,b ~kb,a

~kb,c ~kc,b

~da~db

~dc~d . . . encrypted votes

~da = (da,t1 , da,t2 , . . . , da,t|T | )

da,t = va,t + ka,b,t + ka,c,t

va,t ∈ {0, 1}

Casting of Votes

T, PT, PT, P E-mail

noti�cation

T . . . time slots

P . . . voters

~ka,c ~kc,a

~ka,b ~kb,a

~kb,c ~kc,b

~da~db

~da = (da,t1 , da,t2 , . . . , da,t|T | )

va,t ∈ {0, 1}

Casting of Votes

T, PT, PT, P E-mail

noti�cation

T . . . time slots

P . . . voters

~ka,c ~kc,a

~ka,b ~kb,a

~kb,c ~kc,b

~da~db

~da = (da,t1 , da,t2 , . . . , da,t|T | )

va,t ∈ {0, 1}

Casting of Votes

T, PT, PT, P E-mail

noti�cation

T . . . time slots

P . . . voters

~ka,c ~kc,a

~ka,b ~kb,a

~kb,c ~kc,b

~da~db

~da = (da,t1 , da,t2 , . . . , da,t|T | )

va,t ∈ {0, 1}

Result Publication

T, PT, PT, P E-mail

noti�cation

T . . . time slots

P . . . voters

~ka,c ~kc,a

~ka,b ~kb,a

~kb,c ~kc,b

~da~db

~da,~db~da,~dc~db,~dc E-mail

noti�cation

~db,~dc

da,t1 , . . . , da,t|T |db,t1 , . . . , db,t|T |dc,t1 , . . . , dc,t|T |

Choose timeslot with highest sum!

Result Publication

T, PT, PT, P E-mail

noti�cation

T . . . time slots

P . . . voters

~ka,c ~kc,a

~ka,b ~kb,a

~kb,c ~kc,b

~da~db

noti�cation

~db,~dc

Result Publication

T, PT, PT, P E-mail

noti�cation

T . . . time slots

P . . . voters

~ka,c ~kc,a

~ka,b ~kb,a

~kb,c ~kc,b

~da~db

noti�cation

~db,~dc

va,t1 + ka,b,t1 + ka,c,t1

vb,t1 − ka,b,t1 + kb,c,t1

vc,t1 − ka,c,t1 − kb,c,t1

Result Publication

T, PT, PT, P E-mail

noti�cation

T . . . time slots

P . . . voters

~ka,c ~kc,a

~ka,b ~kb,a

~kb,c ~kc,b

~da~db

noti�cation

~db,~dc

va,t1 + ka,b,t1 + ka,c,t1

+ vb,t1 − ka,b,t1 + kb,c,t1+ vc,t1 − ka,c,t1 − kb,c,t1

Result Publication

T, PT, PT, P E-mail

noti�cation

T . . . time slots

P . . . voters

~ka,c ~kc,a

~ka,b ~kb,a

~kb,c ~kc,b

~da~db

noti�cation

~db,~dc

+ ka,b,t1 + ka,c,t1

+ vb,t1

− ka,b,t1 + kb,c,t1

+ vc,t1

− ka,c,t1 − kb,c,t1

Result Publication

T, PT, PT, P E-mail

noti�cation

T . . . time slots

P . . . voters

~ka,c ~kc,a

~ka,b ~kb,a

~kb,c ~kc,b

~da~db

noti�cation

~db,~dc

∑vi,t1

. . .∑

vi,t|T |

Result Publication

T, PT, PT, P E-mail

noti�cation

T . . . time slots

P . . . voters

~ka,c ~kc,a

~ka,b ~kb,a

~kb,c ~kc,b

~da~db

noti�cation

~db,~dc

∑vi,t1 . . .

∑vi,t|T |

Trying to Cheat

T, PT, PT, P E-mail

noti�cation

T . . . time slots

P . . . voters

~ka,c ~kc,a

~ka,b ~kb,a

~kb,c ~kc,b

~da~db

noti�cation

~da = (da,t1 , da,t2 , . . . , da,t|T | )

va,t ∈ {0, 1}

va,t = −1? va,t = 2?

Trying to Cheat

T, PT, PT, P E-mail

noti�cation

T . . . time slots

P . . . voters

~ka,c ~kc,a

~ka,b ~kb,a

~kb,c ~kc,b

~da~db

noti�cation

~da = (da,t1 , da,t2 , . . . , da,t|T | )

va,t ∈ {0, 1}

va,t = −1? va,t = 2?

Trying to Cheat

T, PT, PT, P E-mail

noti�cation

T . . . time slots

P . . . voters

~ka,c ~kc,a

~ka,b ~kb,a

~kb,c ~kc,b

~da~db

noti�cation

~da = (da,t1 , da,t2 , . . . , da,t|T | )

va,t ∈ {0, 1}

va,t = −1? va,t = 2?

Trying to Cheat

T, PT, PT, P E-mail

noti�cation

T . . . time slots

P . . . voters

~ka,c ~kc,a

~ka,b ~kb,a

~kb,c ~kc,b

~da~db

noti�cation

~da = (da,t1 , da,t2 , . . . , da,t|T | )

va,t ∈ {0, 1}

va,t = −1? va,t = 2?

Avoid −1 Cheaters

T1 T2 T3 T4

Alice 1 1 0 0

Bob 0 1 1 0

Mallory 0 0 1 0∑1 2 2 0

Alice 0 0 0 0

Bob 0 1 0 0

Mallory 0 ? 0 0∑≥ 0?

Alice 0 1 0 0

Bob 0 0 0 0

Mallory 0 ? 0 0∑≥ 0?

Alice 1 0 0 0

Bob 0 0 1 0

Mallory 0 ? 1 0∑≥ 0?

∑1 1 0 0

Avoid −1 Cheaters

T1 T2 T3 T4

Alice 1 1 0 0

Bob 0 1 1 0

Mallory 0 0 1 0∑1 2 2 0

Alice 0 0 0 0

Bob 0 1 0 0

Mallory 0 ? 0 0∑≥ 0?

Alice 0 1 0 0

Bob 0 0 0 0

Mallory 0 ? 0 0∑≥ 0?

Alice 1 0 0 0

Bob 0 0 1 0

Mallory 0 ? 1 0∑≥ 0?

∑1 1 0 0

Avoid −1 Cheaters

T1 T2 T3 T4

Alice 1 1 0 0

Bob 0 1 1 0

Mallory 0 0 1 0∑1 2 2 0

Alice 0 0 0 0

Bob 0 1 0 0

Mallory 0 ? 0 0∑≥ 0?

Alice 0 1 0 0

Bob 0 0 0 0

Mallory 0 ? 0 0∑≥ 0?

Alice 1 0 0 0

Bob 0 0 1 0

Mallory 0 ? 1 0∑≥ 0?

∑1 1 0 0

Avoid −1 Cheaters

T1 T2 T3 T4

Alice 1 1 0 0

Bob 0 1 1 0

Mallory −1−1 1 −1∑0 1 2 −1

Alice 0 0 0 0

Bob 0 1 0 0

Mallory 0 ? 0 0∑≥ 0?

Alice 0 1 0 0

Bob 0 0 0 0

Mallory 0 ? 0 0∑≥ 0?

Alice 1 0 0 0

Bob 0 0 1 0

Mallory 0 ? 1 0∑≥ 0?

∑1 1 0 0

Avoid −1 Cheaters

T1 T2 T3 T4

Alice 1 1 0 0

Bob 0 1 1 0

Mallory 0−1 1 0∑1 1 2 0

Alice 0 0 0 0

Bob 0 1 0 0

Mallory 0 ? 0 0∑≥ 0?

Alice 0 1 0 0

Bob 0 0 0 0

Mallory 0 ? 0 0∑≥ 0?

Alice 1 0 0 0

Bob 0 0 1 0

Mallory 0 ? 1 0∑≥ 0?

∑1 1 0 0

Avoid −1 Cheaters

T1 T2 T3 T4

Alice 1 1 0 0

Bob 0 1 1 0

Mallory 0−1 1 0∑1 1 2 0

Alice 0 0 0 0

Bob 0 1 0 0

Mallory 0 ? 0 0∑≥ 0?

Alice 0 1 0 0

Bob 0 0 0 0

Mallory 0 ? 0 0∑≥ 0?

Alice 1 0 0 0

Bob 0 0 1 0

Mallory 0 ? 1 0∑≥ 0?

∑1 1 0 0

Avoid −1 Cheaters

T1 T2 T3 T4

Alice 1 1 0 0

Bob 0 1 1 0

Mallory 0−1 1 0∑1 1 2 0

Alice 0 0 0 0

Bob 0 1 0 0

Mallory 0 ? 0 0∑≥ 0?

Alice 0 1 0 0

Bob 0 0 0 0

Mallory 0 ? 0 0∑≥ 0?

Alice 1 0 0 0

Bob 0 0 1 0

Mallory 0 ? 1 0∑≥ 0?

∑1 2 1 0

Avoid −1 Cheaters

T1 T2 T3 T4

Alice 1 1 0 0

Bob 0 1 1 0

Mallory 0−1 1 0∑1 1 2 0

Alice 0 0 0 0

Bob 0 1 0 0

Mallory 0 ? 0 0

∑≥ 0?

Alice 0 1 0 0

Bob 0 0 0 0

Mallory 0 ? 0 0

∑≥ 0?

Alice 1 0 0 0

Bob 0 0 1 0

Mallory 0 ? 1 0

∑≥ 0?∑

1 2 1 0

Avoid −1 Cheaters

T1 T2 T3 T4

Alice 1 1 0 0

Bob 0 1 1 0

Mallory 0−1 1 0∑1 1 2 0

Alice 0 0 0 0

Bob 0 1 0 0

Mallory 0 ? 0 0∑≥ 0?

Alice 0 1 0 0

Bob 0 0 0 0

Mallory 0 ? 0 0∑≥ 0?

Alice 1 0 0 0

Bob 0 0 1 0

Mallory 0 ? 1 0∑≥ 0?∑

1 2 2 0

Avoid +2 Cheaters

normal poll

T1 T2 T3 T4

Alice 1 1 0 0

Bob 0 1 1 0

Mallory 0 0 2 0∑1 2 3 0

inverted poll

T1 T2 T3 T4

Alice 0

Mallory 1

1 −1

Avoid +2 Cheaters

normal poll

T1 T2 T3 T4

Alice 1 1 0 0

Bob 0 1 1 0

Mallory 0 0 2 0∑1 2 3 0

inverted poll

T1 T2 T3 T4

Alice 0

Mallory 1

1 −1

Avoid +2 Cheaters

normal poll

T1 T2 T3 T4

Alice 1 1 0 0

Bob 0 1 1 0

Mallory 0 0 2 0∑1 2 3 0

inverted poll

T1 T2 T3 T4

Alice 0

Mallory 1

1 −1

Avoid +2 Cheaters

normal poll

T1 T2 T3 T4

Alice 1 1 0 0

Bob 0 1 1 0

Mallory 0 0 2 0∑1 2 3 0

inverted poll

T1 T2 T3 T4

Alice 0 0

Bob 1 0

Mallory 1 1

∑2 1

∑3 3

Avoid +2 Cheaters

normal poll

T1 T2 T3 T4

Alice 1 1 0 0

Bob 0 1 1 0

Mallory 0 0 2 0∑1 2 3 0

inverted poll

T1 T2 T3 T4

Alice 0 0 1

Bob 1 0 0

Mallory 1 1 −1∑2 1 0

∑3 3 3

Extensions

Problem Statement

Scheme

Extensions

Evaluation

n-lange.de

Simplifying the Key Exchange

T, PT, PT, P E-mail

noti�cation

T . . . time slots

P . . . voters

~ka,c ~kc,a

~ka,b ~kb,a

~kb,c ~kc,b

~da~db

noti�cation

T, PT, PT, P E-mail

noti�cation

T . . . time slots

P . . . voters

~ka,c ~kc,a

~ka,b ~kb,a

~kb,c ~kc,b

~da~db

noti�cation

T, PT, PT, P E-mail

noti�cation

T . . . time slots

P . . . voters

~ka,c ~kc,a

~ka,b ~kb,a

~kb,c ~kc,b

~da~db

noti�cation

Intermezzo � Dif�e�Hellman Key Agreement

secret s

Alice Bob

public

g, qchooses ra

gra mod q

= gra·rb mod q

chooses rb

grb mod q

= gra·rb mod q

Discrete

Logarithm

assumption

x = gr mod q

public

hard to �nd

W. Dif�e and M. E. Hellman, �New Directions in Cryptography,� IEEE Transactions on Information Theory, vol.IT-22, no. 6, pp. 644�654, 1976.

secret s

Alice Bob

public

g, qchooses ra

gra mod q

= gra·rb mod q

chooses rb

grb mod q

= gra·rb mod q

Discrete

Logarithm

assumption

x = gr mod q

public

hard to �nd

secret s

Alice Bob

public

g, qchooses ra

gra mod q

= gra·rb mod q

chooses rb

grb mod q

= gra·rb mod q

Discrete

Logarithm

assumption

x = gr mod q

public

hard to �nd

Intermezzo � Dif�e�Hellman Key Agreementsecret s

Alice Bob

public

g, qchooses ra

gra mod q

= gra·rb mod q

chooses rb

grb mod q

= gra·rb mod q

Discrete

Logarithm

assumption

x = gr mod q

public

hard to �nd

Alice Bobpublic

chooses ra

gra mod q

= gra·rb mod q

chooses rb

grb mod q

= gra·rb mod q

Discrete

Logarithm

assumption

x = gr mod q

public

hard to �nd

Alice Bobpublic

g, qchooses ra

gra mod q

= gra·rb mod q

chooses rb

grb mod q

= gra·rb mod q

Discrete

Logarithm

assumption

x = gr mod q

public

hard to �nd

Alice Bobpublic

g, qchooses ra

gra mod q

= gra·rb mod q

chooses rb

grb mod q

= gra·rb mod q

Discrete

Logarithm

assumption

x = gr mod q

public

hard to �nd

Alice Bobpublic

g, qchooses ra

gra mod q

= gra·rb mod q

chooses rb

grb mod q

= gra·rb mod q

Discrete

Logarithm

assumption

x = gr mod q

public

hard to �nd

Dif�e�Hellman

Alice Bob

key exchange

~ka,c ~k b,

Server

gra grb

grb , grc gra , grc

gra , grb

gra·rb , gra·rc grb·ra , grb·rc

grc ·ra , grc ·rb

gra·rb grb·ra~ka,b

Simplifying the Key ExchangeDif�e�Hellman

Alice Bob

registration

~ka,c ~k b,

Server

gra grb

grb , grc gra , grc

gra , grb

grc ·ra , grc ·rb

Alice Bob

poll initialization

~ka,c ~k b,

Server

gra grb

grb , grc gra , grc

gra , grb

grc ·ra , grc ·rb

Alice Bob

poll initialization

~ka,c ~k b,

cServer

gra grb

grb , grc gra , grc

gra , grb

grc ·ra , grc ·rb

gra·rbpseudorandom

number generator

ka,b,t

ka,b,t1

ka,b,t|T |

tuuid tbl

gra·rbpseudorandom

number generator

ka,b,t

ka,b,t1

ka,b,t|T |

tuuid tbl

gra·rbpseudorandom

number generator

ka,b,t

,tbl~ka,b

ka,b,t1

ka,b,t|T |

tuuid tbl

gra·rbpseudorandom

number generator

ka,b,t

,tbl~ka,b

ka,b,t1

ka,b,t|T |

uuid tbl

gra·rbpseudorandom

number generator

ka,b,t

,tbl~ka,b

ka,b,t1

ka,b,t|T |

gra·rbpseudorandom

number generator

ka,b,t,tbl

ka,b,t1

ka,b,t|T |

tuuid tbl

Dynamic Joining

Dynamic Leaving

Evaluation

Problem Statement

Scheme

Extensions

Evaluation

Simon Day

Evaluation

1 10 00 00 00 10 01 00 0

0 0 1 1

invert

← initialization

→ vote casting

← result publication

. . . Date

scales(|P| − 1 asym. op-erations per voter)

Evaluation

1 10 00 00 00 10 01 00 0

0 0 1 1

invert

← initialization

→ vote casting

. . . Date

Evaluation

1 10 00 00 00 10 01 00 0

0 0 1 1

invert

← initialization

→ vote casting

. . . Date

Evaluation

1 10 00 00 00 10 01 00 0

0 0 1 1

invert

← initialization

→ vote casting

. . . Date

Evaluation

1 10 00 00 00 10 01 00 0

0 0 1 1

invert

← initialization

→ vote casting

. . . Date

Evaluation

1 10 00 00 00 10 01 00 0

0 0 1 1

invert

← initialization

→ vote casting

. . . Date

Problem Statement

Scheme

Extensions

Evaluation

Registration/Login

Poll Initialization

Vote Casting

Dynamic Leaving

Result Publication

• novel scheme for privacy-enhanced

event scheduling

à scales in number of time slots

à no central trust entity

• partially implemented as Web2.0

application

• implement missing features

• validate performance

• more features desirable

Faculty of Computer Science Institute of Systems Architecture, Chair of Privacy and Data Security

Thank you for your attention!

http://dudle.inf.tu-dresden.de

Benjamin.Kellermann@tu-dresden.de

D19E 04A8 8895 020A 8DF60092 3501 1A32 491A 3D9C

Berlin, December 29, 2009

PrimeLife is a research projectfunded by the European Commis-

sion's 7th Framework Programme

• mixes

• blind signatures

• homomorphic encryption

• distributed constraint satisfaction/optimization problem

T. Herlea et al., �On Securely Scheduling a Meeting,� in Trusted Information � The New Decade Challenge(Proc. of IFIP SEC), M. Dupuy and P. Paradinas, Eds., 2001, pp. 183�198.

Computational Complexity

server

no expensive computation needed

client

1 discrete exponentiation (DH)

|P| − 1 discrete exponentiations

1 digital signature

|T | · (|P| − 1) hashes

|T | · (|P| − 1) symmetric decryptions

More Features

• privacy-invasive and

privacy-enhanced together

• prede�ned decision rules

• threshold scheme

• dynamic insertion/deletion of

time slots

• updating/revoking votes

• let voters prove that they signaled

availability for more than a certain

minimum number of time slots

Privacy-Invasive and Privacy-Enhanced

Complex Decision Rules

Privacy-Enhanced Event Scheduling -...

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