  In this literature review, we first briefly provide an introduction on the
privacy aspect of blockchain systems and why it is a difficult quality to
achieve, especially using traditional methods. Next, we go over a wide range of
different strategies and techniques, along with their respective empirical
implementations. Starting with approaches that attempted to provide privacy on
Bitcoin/existing blockchain systems, then going into more advanced techniques,
such as secure multi-party computations, ring signatures, and zero knowledge
proofs, that construct a more advanced blockchain system from scratch with the
objective of preserving privacy. Finally, we conclude that the current state of
privacy on blockchains still needs work for it to be reliable. Nevertheless,
the field of privacy in this domain is developing and advancing at a rapid
rate.
