Anonymous Accounting for Decentralized Systems

175 Pages·2011·1.77 MB·English

Abstract of “Anonymous Accounting for Decentralized Systems”
by C. Chris Erway, Ph.D., Brown University, May 2011
Peer-to-peer systems have been proposed for a wide variety of applications, such as file-sharing,
distributedstorage,anddistributedcomputation. Thesesystemsseekthebenefitsofadecentralized
design—chiefly, the ability of a system to self-scale as new participants join, since participants are
motivated to contribute resources that offset the added workload they generate. Decentralization
also offers improved fault-tolerance and user privacy, because no central authority is responsible for
orchestrating or recording peer interactions.
However, these beneficial system properties are at risk from selfish participants. While many
peer-to-peer systems provide incentives for encouraging participation, past work has shown that
these mechanisms can be gamed by selfish peers that consume resources while providing little or
none in return. For example, the pairwise reputation scheme used by BitTorrent applies only in the
short term of a single download; new peers must be bootstrapped by altruistic service.
A currency-based accounting system provides fungible, long-term incentives for participation
thatpersistbeyondthelimitedscaleofasingledownloadorpairwiseinteraction. However,currency
raises a number of privacy and systems concerns arising from the infrastructure required to support
it. For example, a “bank” must check and count currency, which presents a potential performance
bottleneckandprivacyconcern. Inthedigitalworld,theprivacyofpeerinteractionscanbepreserved
through the use of anonymous, cryptographically secure electronic cash (e-cash).
This thesis shows that e-cash is a practical technique for ensuring fairness, robustness, and
better long-term incentives in decentralized systems. It investigates how to build systems that
anonymously account for three different resource types—bandwidth, storage, and computation—
throughtheapplicationofprotocolsforcryptographicfairexchangeande-cash,andhowtomitigate
the overhead involved in doing so. As a proof of concept, this thesis introduces Cashlib, an open-
source library for e-cash; ZKPDL, a programming language that speeds both the performance and
developmentofcryptographicimplementations;andFairTrader,acurrency-basedfilesharingsystem
that uses e-cash to provide long-term, reliable service for users.
Anonymous Accounting for
Decentralized Systems
by
C. Chris Erway
B. A., Cornell University, 2002
Sc. M., Brown University, 2006
A Dissertation submitted in partial fulfillment of the
requirements for the Degree of Doctor of Philosophy
in the Division of Computer Science at Brown University
Providence, Rhode Island
May 2011
(cid:13)c Copyright 2011 by C. Chris Erway
This dissertation by C. Chris Erway is accepted in its present form
by the Division of Computer Science as satisfying the
dissertation requirement for the degree of Doctor of Philosophy.
Date
John Jannotti, Director
Recommended to the Graduate Council
Date
John Jannotti, Reader
Date
Anna Lysyanskaya, Reader
Date
Roberto Tamassia, Reader
Approved by the Graduate Council
Date
Peter M. Weber, Dean of the Graduate School
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Vitæ
Chris Erway was born in New York City in 1980. He grew up in Maplewood, New Jersey,
and attended its public schools, graduating from Columbia High School in 1998. He was
awarded a double major B.A. in music and computer science from the Cornell University
College of Arts and Sciences in 2002. While at Cornell he also spent a semester in London
in 2001 at the School of Oriental and African Studies, studying East and South Asian music
and the Chinese language.
In 1999, by stroke of luck, Chris found himself a summer intern at VMware—then a
small startup in Palo Alto, California founded by a Stanford professor and his graduate
students—where he learned to write kernel modules and network drivers. This systems
hacking experience sparked his passion for systems and networks, and led to another in-
dustry internship in 2001, working for IBM Research on a parallel I/O-based filesystem
for the Blue Gene supercomputer project. After graduating from Cornell, Chris moved to
New York to join the Blue Gene/L system software team at the IBM T.J. Watson Research
Center in Yorktown Heights, where he worked on the BG/L kernel and networking stack.
This exposure to the world of systems research eventually led Chris back to academia,
andin2004heenrolledatBrownUniversityasaPhDstudentunderadvisorJohnJannotti.
At Brown his research interests shifted from choreographing large, centralized supercom-
puters to decentralized P2P networks, security, and privacy. In 2006 he was a founding
member of the Brownie Points Project, which explored applications of cryptographic e-cash
in network systems. His work on that project forms the basis of this thesis.
In2010, ChrisandtwoBrownCSalumnifoundedastartupcompany, Tracelytics, which
automates the performance analysis of web applications; he will continue to serve as CTO
at Tracelytics after completing his degree. Outside of the world of computing, Chris also
enjoys creating and playing music, and has performed on trombone for the past six years
in the Providence brass-and-drums band What Cheer? Brigade.
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Dedicated to the memory of my grandparents
Dr. Charles Eugene Erway
Edith Mae Daugard Erway
Sywe-Yu Chen 陳學漁
Joyce Teng 鄧幸生
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Acknowledgments
I would first like to thank my advisor, John Jannotti, whom over the years has provided me
with immense perspective and helped hone my instincts and opinions relating to computer
systems and networks. I am deeply indebted for his wisdom, patience, and insight as I have
navigated my research career here at Brown. I am also indebted to my committee members
and collaborators, Anna Lysyanskaya and Roberto Tamassia; without their assistance (and
cryptographic protocols) this thesis would not have been possible.
Muchoftheworkpresentedinthisdissertationwasproducedasaresultofcollaborations
with the other members of the Brownie Points Project: John Jannotti, Anna Lysyanskaya,
Mira Belenkiy, Melissa Chase, Theodora Hinkle, Alptekin Küpçü, Sarah Meiklejohn, and
Eric Rachlin [18, 17]. In particular, the Cashlib/ZKPDL project [125] would not have
been possible without Sarah Meiklejohn, who was instrumental in guiding it from idea
to implementation, as well as Thea Hinkle, and also our summer research collaborators
Gabriel Bender and Alex Hutter. I would also like to thank Charalampos Papamanthou
and Alptekin Küpçü for our fruitful collaboration on proofs of storage [71], which is also
presented in this dissertation.
MytimeatBrownhasbenefitedgreatlyfromtheadviceandfellowshipofmanystudents
here, among them my officemates Glencora Borradaile, Nikos Triandopoulos, Guy Eddon,
Crystal Kahn, and Steve Gomez; fellow grads past and current David McClosky, Peter
Sibley, Yanif Ahmad, Guillaume Marceau, Luc Mercier, Tomer Moscovich, Tori Sweetser,
Stella Frank, Casey Marks, Eric Koskinen, Michael Gaiman, Andy Pavlo, and Carleton
Coffrin (who helped getting our ZKPDL grammar going with ANTLR [143]).
I would never have ended up at Brown without the mentorship of my old co-workers at
IBM Research, among them José Castaños (himself a Brown CS PhD, and a primary factor
in my decision to attend Brown), José Moreira, Gheorghe Almási, and Călin Caşcaval.
Their decision to keep me around at IBM and show me the ropes in a systems research lab
offered an extraordinary privilege for which I will remain forever grateful.
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MylifeinProvidencewouldhavefaredmuchpoorerwithoutthegoodtimessharedwith
Eric Rachlin, Tibet Sprague, Phil Trevvett, David Segal, Harry Siple, Dan Bass, Joseph
Gulezian, and Eric Johnson, and all the current and past members of the What Cheer?
Brigade. I especially must thank Mindy Stock for her emotional support, camaraderie, and
advice. MytimeinNewYorkwouldhavebeenmuchlessstimulatingwithoutBenRansford,
Michael Manning, and Bryan Renne.
I would also like to express my deepest gratitude to my co-founders Spiros Eliopoulos
and Dan Kuebrich, and colleagues Jason Rassi and TR Jordan, for all their support in
holding things down at Tracelytics while I worked to complete this thesis.
MyresearchhasbeensupportedinpartbyfundingfromtheNationalScienceFoundation
Cyber Trust grant program.
Finally, and most importantly, I would like to thank my family for their perpetual
support and encouragement. My parents, Chip and Tina, brought me into this world and
made sure I did well at school. My sister Cathy and uncle Jo-Jo have always been clear-
minded advisors and advocates. This dissertation is dedicated to my grandparents, and I
hope it may honor their memory.
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Contents
Dedication v
1 Introduction 1
1.1 Thesis statement . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2
1.2 Contributions . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2
1.3 Thesis outline . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3
2 Background and related work 4
2.1 Peer-to-peer systems . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4
2.2 BitTorrent . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 5
2.2.1 System overview . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 6
2.2.2 Incentives . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 6
2.2.3 Fairness and performance . . . . . . . . . . . . . . . . . . . . . . . . 7
2.2.4 Free-riding . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 8
2.2.5 Multiple swarms . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 9
2.2.6 Ratio trackers . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 9
2.3 Related work . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 11
2.3.1 P2P currencies . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 11
2.3.2 Reputation systems . . . . . . . . . . . . . . . . . . . . . . . . . . . 12
2.3.3 Distributed computing and grid resource sharing . . . . . . . . . . . 13
2.3.4 Cryptographic programming languages and libraries . . . . . . . . . 14
3 Currency for P2P systems 16
3.1 Currency requirements . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 16
3.1.1 Endorsed e-cash . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 18
3.2 System design . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 20
3.2.1 Bank and arbiter . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 20
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3.2.2 Users . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 21
3.2.3 Obtaining blocks . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 22
3.3 The buy and barter protocols . . . . . . . . . . . . . . . . . . . . . . . . . . 23
3.3.1 How to buy data . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 24
3.3.2 How to barter for data . . . . . . . . . . . . . . . . . . . . . . . . . . 25
3.3.3 How to resolve disputes . . . . . . . . . . . . . . . . . . . . . . . . . 28
3.4 Scaling by bartering . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 30
3.4.1 Batched transactions . . . . . . . . . . . . . . . . . . . . . . . . . . . 32
3.5 Economic Issues . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 32
3.5.1 Entering the Network . . . . . . . . . . . . . . . . . . . . . . . . . . 33
3.5.2 Creation of Money . . . . . . . . . . . . . . . . . . . . . . . . . . . . 33
3.5.3 Variable vs. fixed pricing . . . . . . . . . . . . . . . . . . . . . . . . 34
3.6 Currency for other distributed applications . . . . . . . . . . . . . . . . . . 35
3.6.1 Distributed lookup . . . . . . . . . . . . . . . . . . . . . . . . . . . . 35
3.6.2 Onion routing . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 36
3.6.3 Distributed computation . . . . . . . . . . . . . . . . . . . . . . . . . 36
3.6.4 Distributed storage . . . . . . . . . . . . . . . . . . . . . . . . . . . . 37
4 Accounting for outsourced computation 38
4.1 Model . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 40
4.2 Basic construction . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 41
4.3 Accuracy and hash functions . . . . . . . . . . . . . . . . . . . . . . . . . . 43
4.4 When to check an answer . . . . . . . . . . . . . . . . . . . . . . . . . . . . 45
4.4.1 Double checking . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 46
4.4.2 Hiring multiple contractors . . . . . . . . . . . . . . . . . . . . . . . 46
4.4.3 Hybrid strategy . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 47
4.4.4 Hiring two rational contractors . . . . . . . . . . . . . . . . . . . . . 47
4.5 Malicious contractors . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 49
4.5.1 Independent malicious contractors . . . . . . . . . . . . . . . . . . . 49
4.5.2 Colluding malicious contractors . . . . . . . . . . . . . . . . . . . . . 50
4.6 Evaluation . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 52
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