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Collusion-Resistant Mechanisms with Verification Yielding Optimal Solutions. Carmine Ventre (University of Liverpool) Joint work with: Paolo Penna (University of Salerno). Routing in Networks. s. Change over time (link load). No Input Knowledge. 3. 10. 1. 1. 2. Selfishness.

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collusion resistant mechanisms with verification yielding optimal solutions

Collusion-Resistant Mechanisms with Verification Yielding Optimal Solutions

Carmine Ventre (University of Liverpool)

Joint work with:

Paolo Penna (University of Salerno)

routing in networks
Routing in Networks

s

Change over time (link load)

No Input Knowledge

3

10

1

1

2

Selfishness

Private Cost

2

1

3

7

7

4

1

Internet

mechanisms dealing w selfishness
Mechanisms: Dealing w/ Selfishness

s

  • Augment an algorithm with a payment function
  • The payment function should incentive in telling the truth
  • Design a truthful mechanism

3

10

1

1

2

2

1

3

7

7

4

1

truthful mechanisms

M = (A, P)

Truthful Mechanisms

s

Utility = Payment – cost = – true

M truthful if:

Utility (true, , .... , ) ≥ Utility (bid, , .... , )

for all true, bid, and , ...,

optimization truthful mechanisms
Optimization & Truthful Mechanisms
  • Objectives in contrast
    • Many lower bounds (even for two players and exponential running time mechanisms)
      • Variants of the SPT [Gualà&Proietti, 06]
      • Minimizing weighted sum scheduling [Archer&Tardos, 01]
      • Scheduling Unrelated Machines [Nisan&Ronen, 99], [Christodoulou & Koutsoupias & Vidali 07], …
      • Workload minimization in interdomain routing [Mu’alem & Schapira, 07], [Gamzu, 07]
    • & a brand new computational lower bound
      • CPPP [Papadimitriou &Schapira & Singer, 08]
  • Study of optimal truthful mechanisms
collusion resistant mechanisms
Collusion-Resistant Mechanisms

∑ Utility (true, true, , .... , ) ≥ ∑ Utility (bid, bid, , .... , )

  • CRMs are “impossible” to achieve
    • Posted price [Goldberg & Hartline, 05]
    • Fixed output [Schummer, 02]
      • Unbounded apx ratios

for all true, bid, C and , ...,

in C

in C

Coalition C

+

describing real world collusions
Describing Real World: Collusions
  • “Accused of bribery”
    • 1,030,000 results on Google
    • 1,635 results on Google news
  • Can we design CRMs using real-world information?
describing real world verification
Describing Real World: Verification
  • TCP datagram starts at time t
    • Expected delivery is time t + 1…
    • … but true delivery time is t + 3
  • It is possible to partially verify declarations by observing delivery time
  • Other examples:
    • Distance
    • Amount of traffic
    • Routes availability

TCP

3

1

IDEA ([Nisan & Ronen, 99]): No payment for agents caught by verification

verification setting
Verification Setting
  • Give the payment if the results are given “in time”
    • Agent is selected when reporting bid
    • truebid just wait and get the payment
    • true>bid no payment (punish agent )
crms w verification for single parameter bounded domains
CRMs w/verification for single-parameter bounded domains

s

  • Agents aka as “binary” (in/out outcomes)
    • e.g., controls edges
  • Sufficient Properties
    • Pay all agents(!!!)
    • Algorithm 2-resistant

3

10

1

1

2

2

true

true

10+Pe

11+Pe

1

3

7

Truthfulness

true

Pe’ = 0

e

7

  • e’ has no way to enter the solution by unilaterally lying
  • In coalition they can make the cut really expensive

2

4

1

10

e’

bid

true

UtilityC(bid)=Pe’ – 10

≥ 10 + Pe– 10 > UtilityC(true)

true

UtilityC(true)= Pe – 2

truthful mechanisms w verification the threshold
Truthful Mechanisms w/ Verification: the threshold

bid < in

bid > out

(A,P) truthful with verification

A(bid, )

ths

ths

ths

in

out

bid

[Auletta&De Prisco&Penna&Persiano,04]

2 resistant algorithms
2-resistant Algorithms

t=(true, true, , .... , )

t-=(true , , .... , )

b-=(bid , , .... , )

b=(bid, bid, , .... , )

bid ≥ true

(Verification doesn’t work)

b’ =

t’=

t’

b’

t’

b’

in

ths

ths

ths

ths

out

exploiting verification crms w verification
Exploiting Verification: CRMs w/verification

h - if out

Payment (b) =

h if in

b’

ths

  • (A,Payment) is a CRM w/ verification

Thm. Algorithm A 2-resistant

Proof Idea.

At least one agent is caught by verification

Usage of the constant h for bounded domains

any number between bidmin & bidmax

proof continued
Proof (continued)
  • Each is not worse by truthtelling
  • No agent is caught by verification

h - if out

Payment (b) =

t

b

h if in

in

in

out

in

in

out

out

in

out

out

t’

t’

b’

b’

b’

t’

true

true

ths

ths

ths

ths

ths

ths

  • h - true

= Utility (b)

= Utility (b)

  • h - true ≥ h -

b’

Utility (t) =

Utility (t) =

ths

  • h - ≥ h - true
  • h - ≥ h -
simplifying resistance condition
Simplifying Resistance Condition

t-

b-

b=(bid , , .... , )

b-=(bid , , .... , )

b=(bid, bid, , .... , )

t-=(true , , .... , )

t=(true, true, , .... , )

t=(true , , .... , )

bid ≥ true

(Verification doesn’t work)

bid ≥ true

b’ =

b’ =

t’=

t’=

in

Optimal CRMs

t’

t’

b’

b’

b’

t’

out

in

ths

ths

ths

ths

ths

ths

Thm. Optimal threshold-monotone algorithms with fixed tie breaking are n-resistant

out

applications
Applications
  • Optimal CRMs for:
    • MST
    • k-items auctions
    • Cheaper payments wrt [Penna&V,08]
  • Optimal truthful mechanisms for multidimensional agents bidding from bounded domains and non-decreasing cost functions of the form

Cost(bid , ..., bid )

multidimensional agents
Multidimensional Agents

Outcomes = {X1, ..., Xm}

View bid as a virtual coalition C of m single-parameter agents

bid =(bid(X1), .... ,bid(Xm))

b=(bid , ..., bid )

B(b) optimal algorithm with fixed tie breaking rule

A(bid ) m single-player functions

P (b) = ∑ payment (bid )

in C

Lemma. If every A is m-resistant then (B,P) is truthful

Thm. For non-decreasing cost function of the form

Cost(bid , ..., bid )

every A is threshold-monotone

Every A is m-resistant

(B,P) is truthful

conclusions
Conclusions
  • Optimal CRMs with verification for single-parameter bounded domains
  • Optimal truthful mechanisms for multidimensional bounded domains
    • Construction tight (removing any of the hypothesis we get an impossibility result)
  • Overcome many impossibility results by using a real-world hypothesis (verification)
  • For finite domains: Mechanisms polytimeif algorithm is
  • Can we deal with unbounded domains?
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