# Blockchain-based Multifactor Authentication for Future 6G Cellular Networks: A Systematic Review
## 1 Introduction
It is anticipated that the 6G mobile networks will be virtualized through cloud-based systems and is software-defined, intending to ubiquitously connect several heterogeneous devices like the Internet of everything, to enable a significant range of different network services. With this shift of the paradigm towards the 6G network, blockchain and the Internet of Things play a critical role in enabling the applications that connect the cyberspace of the communication world with the physical devices [20; 21]. The future generation of wireless networks supports data-intensive and real-time applications that involve sustainable business models, network orchestration, agile management, spectrum sharing, network slicing, and several other vertical services, so the researchers and experts are increasingly focusing on these terms and systems now [11]. Based on the increasing trends towards the usage of blockchain-based multifactor authentication and a 6G cellular network, the objectives of the study are: (1) to explain and define the blockchain, Multi-factor Authentication, 6G, and the benefits blockchain integration of in 6G, (2) to explore current strategies for the use of blockchain-enabled MFA, and (3) to suggest how the integration of blockchain-enabled MFA would be beneficial for 6G. This study will be a significant addition to the existing literature on blockchain, multifactor authentication, and 6G networks, as it differs from other reviews available in the domain. The current study uses a systematic review style to collect, organize and present information extracted from the reviewed articles published between 2015 and 2021; thus, the study provides more up-to-date and recent information. The selected journal will be reviewed based on different aspects, including the studies' strengths, weaknesses, methodologies, data sets, and evaluation metrics. Furthermore, based on the review of the relevant articles and studies, this study provides details regarding the recent trends related to blockchain-based multifactor authentication and 6G cellular network strategies and integration. Based on these, the study includes the limitations and future indications. This study significantly contributes to explaining the multifactor authentication, blockchain and 6G-based phenomenon, strategies, integrations, and benefits and helping the users in decision-making processes regarding the adoption of the up-to-date systems of blockchain, multifactor authentication 6G mobile networks. Table 1 represents the comparison of the study with the other similar and relevant review articles. The table represents whether or not the study in comparison is a systematic study, blockchain-focused, MFA-focused, 6G-focused, and focused on future trends of these technologies. The rest of the paper is organized as follows: Section 2 details the research methodology used in this research. Section 3 discusses the 6G cellular concepts and security needs. Section 4 explains the Multifactor authentication schemes, followed by a blockchain discussion in Section 5. Section 6 provides details regarding recent studies that have listed some MFA techniques or applications of MFA to a blockchain. Section 7 details the observation based on this review study to highlight the current and future trends and the research challenges. Finally, Section 8 concludes this research study.