Game Authority for Robust and Scalable

Distributed Selfish-Computer Systems

Shlomi Dolev, BGU (Israel)Elad M. Schiller, Chalmers

(Sweden)Paul G. Spirakis, CTI (Greece)

Philippas Tsigas, Chalmers (Sweden)

The system designer

Distributed computing assumes identical programs.

How to design distributed algorithms for the wild

internet?

Let’s play the prisoner dilemma game.

Use game theory for selfish-computer systems.

The system designer

BA Silent Betray

Silent

Betray

(+1,

+1)

(+3,

–1)

(–1,

+3)

( 0, 0

)

John Nash

Game theory predicts: selfish-computer choose

betray!

Yes, I trust game theory.OK... Let’s play

in a real system.

The system designer

We need a distributed game authority.

O.K., we should explicitly enforce the implicit rules of the game.

In a real system, where I am the only

authority…

they would be free to escape!

The Society Moral Code

• Complete anarchy exists without moral codes• Game authority founded over the moral majority

– choose and enforces the rules of the game– promote freedom of choice for the society’s benefit

• We promote honestly selfish behavior for the sake of:• end-point creativity• motivation for success

The Society Moral Code

• Complete anarchy exists without moral codes• Game authority founded over the moral majority

– choose and enforces the rules of the game– promote freedom of choice for the society’s benefit

Benefits • End-point success

• that yields global success

• Provable scalability• from the days of

Greece • Provable robustness, still

Technical Contributions

Cost Reduction: • We replace the higher price of anarchy

with the lower price of stability!

Technical Contributions

Cost Reduction: • We replace the higher price of anarchy

with the lower price of stability!

Price of anarchy (PoA) • Worst case ratio

between:

NE’s social cost, and

the social optimum

Koutsoupias & Papadimitriou STACS’99

Social optimum

Worst NE

PoA

Good Bad

Technical Contributions

Social optimum Best NE

PoS

Good Bad

Price of stability (PoS)• Best case ratio between:

NE’s social cost, and

the social optimum

Anshelevich et al. FOCS'04

Worst NE

PoA

Cost Reduction: • We replace the higher price of anarchy

with the lower price of stability!

Game Authority Implementation

• Can we assume that all components are selfish?– impossible: Phy. layer game & Mac layer game &, … ,

& possible failures & imprecise utility • how to bound the PoA?

Social optimum Best NE

PoS

Good Bad

• Honest and moral based middleware tolerating • Byzantine faults• transient faults

• Facilitates interaction among honestly selfish agents

Worst NE

PoA Explicit

∞

Moral Code

Middleware: Game Authority

Application-layer:

Honestly selfish agents (majority)

Implementation (cont.)

• Byzantine agreement • Cryptographic primitives• Game theory analysis

• How to decide on the preferable game? • How does the honest majority audit the game?• How to preserve privacy in simultaneous plays?

Your attention is appreciated

More details:Technical report number TR-2006:9Computer Science and Engineering Chalmers University of technology, 2006Also, technical report, DELIS, 2006. Accessible via http://delis.upb.de/docs/

Rabbi Akiva said: All is foreseen, but freedom of choice is given. The world is judged in goodness, yet all is proportioned to one's work. (Mishnah Pirkei Avot, Chapter 3, 19)

הכול צפוי, והרשות נתונה; ובטוב העולם נידון.  והכול פרקי (. לפי רוב המעשה, אבל לא על פי המעשה

אבות, ג` ט"ו)