Understanding and Designing for Trust in Bitcoin Blockchain Irni Eliana Khairuddin This dissertation is submitted for the degree of Doctor of Philosophy April 2019 School of Computing and Communications Declaration This thesis has not been submitted in support of an application for another degree at this or any other university. It is the result of my own work and includes nothing that is the outcome of work done in collaboration except where specifically indicated. Many of the ideas in this thesis were the product of discussion with my supervisor Professor Corina Sas. The work in this thesis has not been published anywhere else except in the following publications: 1. Corina Sas and Irni Eliana Khairuddin. 2015. Exploring Trust in Bitcoin Technology: A Framework for HCI Research. In Proceedings of the Annual Meeting of the Australian Special Interest Group for Computer Human Interaction (OzCHI '15), Bernd Ploderer, Marcus Carter, Martin Gibbs, Wally Smith, and Frank Vetere (Eds.). ACM, New York, NY, USA, 338-342. DOI=http://dx.doi.org/10.1145/2838739.2838821 * Irni Khairuddin contributed to the design of the study, conducted the literature review, an initial design of the framework, and produced a first draft. Corina Sas proposed the study, contributed to the design of the study, produced revision of the framework and of the manuscript. 2. Irni Eliana Khairuddin, Corina Sas, Sarah Clinch, and Nigel Davies. 2016. Exploring Motivations for Bitcoin Technology Usage. In Proceedings of the 2016 CHI Conference Extended Abstracts on Human Factors in Computing Systems (CHI EA '16). ACM, New York, NY, USA, 2872-2878. DOI=http://dx.doi.org/10.1145/2851581.2892500 * Irni Khairuddin contributed to the design of the study, conducted the study, transcribed the interviews, analysed the data, and produced iterative drafts of the manuscript. Corina Sas proposed the study, contributed to the design of the study, and critically revised the drafts 3. Corina Sas and Irni Eliana Khairuddin. 2017. Design for Trust: An Exploration of the Challenges and Opportunities of Bitcoin Users. In Proceedings of the 2017 CHI Conference on Human Factors in Computing Systems (CHI '17). ACM, New York, NY, USA, 6499- 6510. DOI: https://doi.org/10.1145/3025453.3025886 * Irni Khairuddin contributed to the design of the study, conducted the study, transcribed the interviews, an initial data analysis, and produced a first draft of the manuscript. Corina Sas proposed the study, contributed to the design of the study, produced revision of data analysis and of the manuscript. 2 4. Irni Eliana Khairuddin and Corina Sas. 2019. Exploration of Bitcoin Mining Practices: Miners’ Trust Challenges and Motivations. In Proceedings of the 2019 CHI Conference on Human Factors in Computing Systems (CHI '19). ACM, New York, NY, USA, DOI: https://doi.org/10.1145/3290605.3300859 * Irni Khairuddin contributed to the design of the study, conducted the study, transcribed the interviews, analysed the data, and produced iterative drafts of the manuscript. Corina Sas proposed the study, contributed to the design of the study, and critically revised the drafts of the manuscripts. 5. Irni Eliana Khairuddin, Corina Sas and Chris Speed. 2019. BlocKit: A Physical Kit for Materializing and Designing for Blockchain Infrastructure. In Proceeding of the 2019 Designing Interactive System Conference (DIS ’19). ACM New York, NY, USA, DOI: https://doi.org/10.1145/3322276.332237 * Irni Khairuddin contributed to the design of the study, iterative design and built the physical kit, conducted the study, transcribed the interviews, an initial data analysis, and produced iterative drafts of the manuscript. Corina Sas proposed the study, contributed to the design of the study and the physical kit, supported the refinement of data analysis, and critically revised the drafts of the manuscripts. All studies have received appropriate ethics approval, and the relevant ethics documentation can be found in Appendices A, B and C. 3 Understanding and Designing for Trust in Bitcoin Blockchain Irni Eliana Khairuddin This thesis is submitted for the degree of Doctor of Philosophy School of Computing and Communications April 2019 Abstract Bitcoin is a cryptocurrency that has created a new revolution in peer-to-peer technology. Built upon decentralised technology known as Blockchain, it supports transparent, fast, cost-effective and irreversible transactions, without the need for trusting the third-party financial institution. The privacy of Bitcoin users is protected, by the pseudoanonymous transaction. At present, Bitcoin holds the largest market share in cryptocurrency and the Blockchain technology had captured the interest of multi-corporations, such as Microsoft, Dell, and T-Mobile. However, Bitcoins have no legal tender in most and it is even worse with the illicit use by the irresponsible people and the cyber-attacks towards the application. Hence, these are the primary motivation of this Ph.D. work, to explore the trust between people and Bitcoin technology as well as identify the opportunities to design for the trust challenges. This thesis investigates the challenges and design works with 80 Bitcoin stakeholders such as users, miners, Blockchain experts and novices in six different but interrelated studies. The first and second studies report in-depth preliminary studies with 20 Bitcoin users and 20 miners to identify the trust challenges in people’s daily practices in using Bitcoin. Based on the findings, users’ risk related to dishonest partner in peer-to-peer Bitcoins transactions is the highlighted trust challenges to be addressed in this thesis. With a strong understanding of Bitcoin mining process, a 4 physical Blockchain design kit, namely BlocKit was developed based on the embodied cognition theories and material centred design. This BlocKit was evaluated by 15 Bitcoin Blockchain’s experienced users and one of the important outcomes proposed the principles to design for trust application in peer-to-peer Bitcoins transactions. Later the algorithms of trust for Bitcoin application were developed based on the suggested principles and were validated by 10 Bitcoin Blockchain’s experienced users. Finally, based on the designed algorithms as well as a newly identified heuristic evaluation for trust, a mock-up prototype of Bitcoin wallet application namely, BitXFps was developed and the interface was evaluated for trust by 15 Bitcoin Blockchain’s experienced users. 5 Acknowledgements بِ ْس ِم هَّللاِ ال هر ْح َم ِن ال هر ِحيم Alhamdulilah, all praise to the most Gracious and Merciful Almighty who makes this journey possible, without whom nothing is possible. First and foremost I would like to dedicate my sincere appreciation to my supervisor Prof. Corina Sas for her valuable advice and for his regular supervisions during my PhD study. Prof. Corina has shown lots of enthusiasms and encouragement towards my work, which motivated me to go even further. I feel lucky to have her as my supervisor as her support has been mostly invaluable for me. I would also like to express my sincere gratitude to my officemate Dr Vatsalla, Dr Faiza, Dr Roberto, Dr Richards, Dr Abdussalam, Dr Izhar, Paul, Wyatt and Alex for their support and advice for work and personal. I am so lucky to have a supportive friendly and pleasant working environment. My sincere thanks to my beloved husband, Rihan Mohamad for his unconditional love and supported me a lot through thick and thin during my study. Not to forget, our beloved daughter, Raina Izzqaireen Rihan, for being good and understanding daughter. Also, to my beloved parents Khairuddin Mohamad and Roselinah Ismail, I am thankful for their love, prayers and for believing in my ability to undertake a PhD degree. I am also thankful to my siblings for their love and support. Finally, to my beloved best friend, Ayu and her little family, thank you so much for the love and support. Also to Pandora Chics Lancaster, Kak Ju, Kak Azliza, Anis and Liana, thank you for lending me your shoulder. Not to forget my beloved sisters in Malaysia, Mazlina, Rina and Maryam, thank you for everything. Last but not least, thank you to my sponsorship, Universiti Teknologi MARA and The Ministry of Education Malaysia for making my dream come true. 6 List of Figures Figure 1.1 Thesis Structure ................................................................................................................... 27 Figure 2.1: Chapter 2 of Thesis Structure ............................................................................................. 28 Figure 2.2: Research Framework for Exploring Levels of Trust in Bitcoin Technology (left) and across Stakeholders Groups (right) (Sas and Khairuddin, 2015) ...................................................................... 52 Figure 2.3: Framework for the material-centred interaction design method (Wiberg & Mikael, 2014) .............................................................................................................................................................. 72 Figure 3.1: Chapter 3 of Thesis Structure ............................................................................................. 74 Figure 3.2: Research Strategies (De Villiers, 2005) ............................................................................... 80 Figure 4.1: Chapter 4 of Thesis Structure ............................................................................................. 92 Figure 4.2: Merchant’s Sign for Accepting Bitcoin Payment ...............................................................