A Blockchain Implementation for Configurable Multi-Factor Challenge-Set Self-Sovereign Identity Authentication Alex Norta Tallinn University, Tallinn, Estonia Johannes Kepler University, Linz, Austria Dymaxion O ¨ U, Tallinn, Estonia alex.norta.phd@ieee.org Alexandr Kormiltsyn Dymaxion O ¨ U, Tallinn, Estonia alexandrkormiltsyn@gmail.com Chibuzor Udokwu University of Applied Sciences Upper Austria, Steyr, Austria Dymaxion O ¨ U, Tallinn, Estonia chibuzor.udokwu@gmail.com Vimal Dwivedi University of Tartu, Tartu, Estonia Dymaxion O ¨ U, Tallinn, Estonia) vimal.bncet@gmail.com Sunday Aroh Dymaxion O ¨ U, Tallinn, Estonia asmelitus@gmail.com Ignas Nikolajev Dymaxion O ¨ U, Tallinn, Estonia ignas.nikolajev@gmail.com Abstract—Multi-factor challenge-set self-sovereign identity au- thentication (MFSSIA) is an important part for establishing trust between systems, devices, organizations and humans for the emerging machine-to-everything (M2X) economy. Most systems for identity authentication (IA) are single sign-on (SSO), or have fixed challenge sets of limited degree. Additionally, IA systems are controlled by governments, or corporations that are closely affiliated with government entities. The available systems for self- sovereign IA do not offer the necessary flexible configurability of challenge sets. Based on research publications about a formal MFSSIA protocol, this paper presents a blockchain employing implementation for a running case assuming different smart- contract blockchain systems must be connected for sensitive data exchange. The prototype offers a marketplace for challenge- set creation and the challenge/response-lifecycle management employs decentralized knowledge graphs (DKG) together with oracles for response evaluations. Index Terms—Blockchain, multi-factor, identity, authentica- tion, self-sovereign I. I NTRODUCTION Over the last two years, governments have eliminated many fundamental liberties and freedoms of citizens to diffuse identity-authentication (IA) apps for exerting societal control 1 . Once such apps are in place, governments are quickly driven to assign to such IA also social credit-score systems 2 that add further restrictions to members of the public. Furthermore, we observe too the emergence of the so-called machine- to-everything (M2X) economy [13] that is defined as ”the result of interactions, transactions, collaborations and busi- ness enactments among humans, autonomous and cooperative smart devices, software agents, and physical systems. The corresponding ecosystem is formed by automated, globally- available, heterogeneous socio-technical e-governance systems 1 https://terviseamet.ee/en/digital-covid-certificate 2 https://tinyurl.com/scs-italy with loosely coupled, peer-to-peer (P2P)-resembling network structures and is characterized by its dynamic, continuously changing, interoperable, open and distributed nature. Thereby, the M2X Economy employs concepts such as cyber-physical systems, the Internet of Things, and wireless sensor networks.” Single sign-on IA is, consequently, not adequate for the complex trust-establishment needs in collaborations between diverse systems, devices, organizations and humans. The foundation for the blockchain-based implementation of the multi-factor challenge-set self-sovereign identity au- thentication (MFSSIA) application is first a publication [12] in which the requirements are defined and subsequently, a deduced Colored Petri Net (CPN) [10] model formalizes the corresponding MFSSIA lifecycle. This first MFSSIA protocol version we further validate for security flaws [14] to update the requirement sets and deduce again the fortified and formalized MFSSIA protocol. We next explain in [13] why MFSSIA is essential for trust resolution to enable collaborations in a M2X economy, e.g., smart cities, Industry 4.0, e-healthcare, and so on. The state of the art shows theoretical MFSSIA protocol results exist for which the ideal deployment technology is blockchains [2]. Informally and briefly, blockchains are dis- tributed ledgers of linked blocks that store consensually events in an immutably traceable way. The extension of blockchains with programming languages yield smart-contract systems [9]. For enabling data exchange between smart contracts and the blockchain-external system context, oracles [1] are employed. Given the vast blockchain-technology spectrum, this paper answers the research questions how to implement and deploy MFSSIA with novel blockchain technologies? This paper answers the question by first giving a hypo- thetical running case in Section II together with background literature. In Section III, the MFSSIA architecture is described,