  We increasingly live in a world where there is a balance between the rights
to privacy and the requirements for consent, and the rights of society to
protect itself. Within this world, there is an ever-increasing requirement to
protect the identities involved within financial transactions, but this makes
things increasingly difficult for law enforcement agencies, especially in terms
of financial fraud and money laundering. This paper reviews the
state-of-the-art in terms of the methods of privacy that are being used within
cryptocurrency transactions, and in the challenges that law enforcement face.
