  The blockchain technology has been rapidly growing since Bitcoin was invented
in 2008. The most common type of blockchain systems, public (permisionless)
blockchain systems have some unique features that lead to a tension with
European Union's General Data Protection Regulation (GDPR) and other similar
data protection laws. In this paper, we report the results of a systematic
literature review (SLR) on 114 research papers discussing and/or addressing
such a tension. To be the best of our know, our SLR is the most comprehensive
review of this topic, leading a more in-depth and broader analysis of related
research work on this important topic. Our results revealed that three main
types of issues: (i) difficulties in exercising data subjects' rights such as
the `right to be forgotten' (RTBF) due to the immutable nature of public
blockchains; (ii) difficulties in identifying roles and responsibilities in the
public blockchain data processing ecosystem (particularly on the identification
of data controllers and data processors); (iii) ambiguities regarding the
application of the relevant law(s) due to the distributed nature of
blockchains. Our work also led to a better understanding of solutions for
improving the GDPR compliance of public blockchain systems. Our work can help
inform not only blockchain researchers and developers, but also policy makers
and law markers to consider how to reconcile the tension between public
blockchain systems and data protection laws (the GDPR and beyond).
