A Review of Offline Blockchain Transaction Systems

Abstract

Blockchain systems rely on stable network connectivity to ensure secure and tamper-proof transactions. While this works well in areas with reliable network connectivity, it can limit blockchain's functionality in remote areas or during natural disasters. Over the years, blockchain-based digital currencies have gained popularity as a means of payment. In order for digital currencies to be comparable with physical cash, blockchain systems need to adopt and support offline transactions. To address these issues, researchers are exploring the potential of offline blockchain systems. In this paper, we provide a systematic study on offline blockchain implementations. We present the various security and privacy issues that arise from the absence of network connectivity in blockchain systems. To better understand the offline blockchain implementations, we provide a systematic and novel categorisation of the various methodologies and analyse how different combinations of methods are used together. Additionally, we outline a three-phase framework that systematically maps security risks to each execution phase of offline blockchain systems. Furthermore, a comparative analysis of the literature based on the security and privacy issues addressed is provided, and a discussion on the research gaps and the current state of offline blockchain systems is summarised.