Securing Communications in an Anonymous Overlay Network By Simon Wilkinson B.C.S. A thesis submitted to the Faculty of Graduate Studies and Research in partial fulfillment of the requirements for the degree of Master of Computer Science At Ottawa-Carleton Institute for Computer Science Carleton University Ottawa, Ontario April 2007 © Copyright by Simon Wilkinson, 2007 Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. 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The author retains copyright L'auteur conserve la propriete du droit d'auteur ownership and moral rights in et des droits moraux qui protege cette these. this thesis. Neither the thesis Ni la these ni des extraits substantiels de nor substantial extracts from it celle-ci ne doivent etre imprimes ou autrement may be printed or otherwise reproduits sans son autorisation. reproduced without the author's permission. In compliance with the Canadian Conformement a la loi canadienne Privacy Act some supporting sur la protection de la vie privee, forms may have been removed quelques formulaires secondaires from this thesis. ont ete enleves de cette these. While these forms may be included Bien que ces formulaires in the document page count, aient inclus dans la pagination, their removal does not represent il n'y aura aucun contenu manquant. any loss of content from the thesis. i * i Canada Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. Abstract Anonymous message sending techniques define a rapidly evolving area in privacy research. Most current systems address only specific aspects of security and privacy. This thesis presents a protocol that addresses all applicable aspects within an anonymous network, and remains secure even in the face of multiple colluding adversaries. The use of techniques such as secret sharing and adaptive routing across disjoint paths through the use of swarm inspired techniques provide multiple tiers of security for all aspects, creating a system with no single point of failure. Simulation results show the effectiveness of these techniques, while also demonstrating that the overhead incurred through the introduction of these anonymity and security measures is within an acceptable range. The concepts and algorithms developed within this thesis have applications beyond those presented herein, and ideas for future directions and improvements are examined. Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. Acknowledgements I would like to thank my supervisors, Tony White and Evangelos Kranakis, for their guidance, patience and support. Their assistance from formulating the base concepts presented in this thesis, up to the fine tuning of the final document was greatly appreciated. Having the opportunity to utilize their knowledge and expertise has been a tremendous benefit, and played a crucial role in making this thesis what it is. To my fiance Amber, my parents John and Regina, my sister Antje, and my soon to be in-laws Mitch and Vanessa, thank you for your love and support. Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. Table of Contents Abstract .................................................................................................................................. ii Acknowledgements ..............................................................................................................iii Table of Contents................................................................................................................. iv List of Tables...................................................................................................................... vii List of Figures.................................................................................................................... viii List of Equations................................................................................................................... x List of Acronyms................................................................................................................. xi Chapter 1 Introduction.......................................................................................................... 1 1.1 Problem and Motivation.............................................................................................1 1.2 Contributions............................................................................................................... 2 1.3 Outline..........................................................................................................................3 Chapter 2 Background .......................................................................................................... 5 2.1 Network Security........................................................................................................5 2.1.1 Privacy ................................................................................................................. 7 2.1.2 Data Integrity.....................................................................................................10 2.2 Threshold Schemes...................................................................................................10 2.3 Peer-to-Peer Networks..............................................................................................12 2.3.1 Overlay Classifications..................................................................................... 13 2.3.2 Anonymous Peer-to-Peer Networks................................................................ 15 2.4 Anonymity.................................................................................................................17 2.4.1 The Adversary .................................................................................................... 17 2.4.1.1 Group of Colluding Nodes.........................................................................19 2.4.2 Views of Anonymity......................................................................................... 21 2.4.3 Degrees of Anonymity......................................................................................22 2.4.4 Attacks on Anonymity......................................................................................24 2.4 Swarm-Based Routing............................................................................................. 26 2.5 Conclusion................................................................................................................ 30 Chapter 3 State of the Art in Anonymous and Adaptive Routing...................................32 3.1 Various Anonymity Building Blocks.................................................................... 32 3.2 Freenet: An Anonymous Storage and Retrieval System........................................36 3.2.1.1 Identity Protection......................................................................................39 3.2.1.2 Data Confidentiality...................................................................................43 3.2.1.3 Data Integrity............................................................................................. 43 3.3 MIX Networks..........................................................................................................44 iv Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. 3.3.1 Free Haven: Distributed Anonymous Storage Service ...................................44 3.3.1.1 Identity Protection......................................................................................46 3.3.1.2 Data Confidentiality...................................................................................47 3.3.1.3 Data Integrity............................................................................................. 47 3.4 Onion Routing...........................................................................................................48 3.4.1 Tor: The Second-Generation Onion Router.................................................... 48 3.4.1.1 Identity Protection...................................................................................... 51 3.4.1.2 Data Confidentiality...................................................................................53 3.4.1.3 Data Integrity............................................................................................