Trust in decentralized anonymous marketplaces

123 Pages·2015·7.12 MB·English

by  Dionysis Zindros

National Technical University of Athens
School of Electrical and Computer Engineering
Department of Computer Science

Trust in decentralized anonymous
marketplaces

Dionysis S. Zindros

November 2015
Advisor: Aris Pagourtzis, Assistant Professor
2
National Technical University of Athens
School of Electrical and Computer Engineering
Department of Computer Science

Trust in decentralized anonymous
marketplaces
Dionysis S. Zindros

Aris Pagourtzis – Principal Advisor,
National Technical University of Athens

Stathis Zachos,
National Technical University of Athens

Aggelos Kiayias,
National and Kapodistrian University of Athens
Dionysis S. Zindros,
Diploma in Electrical and Computer Engineering,
National Technical University of Athens.
The views and opinions expressed in this work are those of the author and do not
necessarily reflect the official policy or position of the National Technical University of
Athens.
Copyright © 2014 - 2015 Dionysis S. Zindros.
Some rights reserved. See Appendix A.
4
Table of Contents
Trust in decentralized anonymous marketplaces 1
Trust in decentralized anonymous marketplaces 3
Table of Contents 5
List of figures 9
List of tables 11
List of code listings 12
Abstract (Greek) 13
Abstract 14
Keywords 15
Acknowledgements 16
Introduction 17
Marketplaces 17
Decentralization 17
Anonymity and pseudonymity 20
A decentralized anonymous marketplace 21
Our contributions 21
History 22
Webs-of-trust 22
Economic origins of money and trade 22
History of online trade 23
History of OpenBazaar 24
Primitives 26
Blockchain primitives 26
Hash primitives 26
Bitcoin 28
Introduction 28
The problem 28
5
Bitcoin history 30
The idea behind Bitcoin 30
Decentralization 31
Payment schema 31
Anonymity 32
Technical bitcoin background 33
Double spending 34
Proof of work 35
Mining 38
Technical details 39
The Bitcoin DAG 40
The Bitcoin script 43
Multisig 45
Multiple transaction inputs 45
Threat model 47
Assumed adversaries 47
Malicious users 47
Malicious corporations 48
Malicious governments 48
Malicious developers 50
Secure development model 51
Testing and automated build 51
Open source 51
Reviewing process 52
Web-of-trust 53
A modified web-of-trust 54
A naive solution 55
Partial topological knowledge 55
Trust association 55
6
Trust transitivity 56
A comparison to other webs-of-trust 57
Bootstrapping the web-of-trust 58
Graph separator attack 58
Topology detection through queries 60
Global trust 62
Proof-of-donation 63
Proof-to-miner 64
Proof-of-burn 65
Almost-collision coin burning 67
Proof-of-timelock 72
Total trust 73
Unbreachable contracts 75
Ricardian contracts 75
Game theoretic primitives 77
2-of-2 trades 78
2-of-3 trades 81
MAD trades 83
Man-in-the-middle loss of anonymity 86
Vendor-in-the-middle attack 87
Friendly names 91
GUIDs 92
Zooko’s Triangle 92
Namecoin 95
OpenBazaar and Namecoin Integration 96
Further research 101
Trusted roles 101
Feedback and reviews 101
Association with other identity systems 102
7
Turing complete blockchains 104
Trust-as-risk 104
Trust propagation and storage 104
Circular trust propagation and convergence 104
Ethical considerations 106
Conclusion 108
Bibliography 109
Appendix: Relicensing OpenBazaar under MIT 118
Appendix: Creative Commons Attribution 4.0 International Public License 119
Section 1 – Definitions 119
Section 2 – Scope 120
Section 3 – License Conditions 121
Section 4 – Sui Generis Database Rights 122
Section 5 – Disclaimer of Warranties and Limitation of Liability 122
Section 6 – Term and Termination 122
Section 7 – Other Terms and Conditions 123
Section 8 – Interpretation 123

8
List of figures
Figure 1: Centralized and Decentralized systems .................................................................................... 19
Figure 2: Chain of coin transactions in bitcoin .......................................................................................... 34
Figure 3: A Proof-Of-Work chain of blocks in bitcoin ............................................................................. 35
Figure 4: The Proof-Of-Work protocol .......................................................................................................... 36
Figure 5: A bitcoin blockchain with some orphan forks ........................................................................ 38
Figure 6: Total bitcoins over time ................................................................................................................... 39
Figure 7: A bitcoin transaction node .............................................................................................................. 40
Figure 8: A coinbase transaction ..................................................................................................................... 41
Figure 9: An unspent transaction output ..................................................................................................... 41
Figure 10: A complete bitcoin transaction graph ..................................................................................... 42
Figure 11: A double spend .................................................................................................................................. 42
Figure 12: An unspent pay-to-pubkey-hash transaction ...................................................................... 44
Figure 13: A 2-of-3 multisig transaction ...................................................................................................... 45
Figure 14: A Graph Separator on the web-of-trust .................................................................................. 59
Figure 15: The Proof-Of-Donation attack feedback loop ...................................................................... 63
Figure 16: A proof-to-miner transaction ...................................................................................................... 64
Figure 17: The global trust function for c = 0.4 ......................................................................................... 66
Figure 18: A Proof-Of-Burn transaction ....................................................................................................... 67
Figure 19: The standard bitcoin address generation algorithm (Courtesy Etotheipi) ............ 69
Figure 20: OpenBazaar provably unspendable address generation ................................................ 70
Figure 21: The 2-of-2 trade in the commit step ........................................................................................ 79
Figure 22: The 2-of-2 Trade after finalization ........................................................................................... 79
Figure 23: A correctly completed 2-of-3 Trade after finalization ..................................................... 82
Figure 24: Dispute resolution through 2-of-3 Trade arbitration with forced finalization ..... 82
Figure 25: Dispute resolution through 2-of-3 Trade arbitration with reversal .......................... 83
Figure 26: A MAD trade after the commit stage ........................................................................................ 84
Figure 27: A MAD trade after finalization .................................................................................................... 85
9
Figure 28: The Vendor-In-The-Middle attack ............................................................................................. 89
Figure 29: Zooko's Triangle ................................................................................................................................ 93

10