  The scientific interest in the area of Decentralized Randomness Beacon (DRB)
protocols has been thriving recently. Partially that interest is due to the
success of the disruptive technologies introduced by modern cryptography, such
as cryptocurrencies, blockchain technologies, and decentralized finances, where
there is an enormous need for a public, reliable, trusted, verifiable, and
distributed source of randomness. On the other hand, recent advancements in the
development of new cryptographic primitives brought a huge interest in
constructing a plethora of DRB protocols differing in design and underlying
primitives.
  To the best of our knowledge, no systematic and comprehensive work
systematizes and analyzes the existing DRB protocols. Therefore, we present a
Systematization of Knowledge (SoK) intending to structure the multi-faced body
of research on DRB protocols. In this SoK, we delineate the DRB protocols along
the following axes: their underlying primitive, properties, and security. This
SoK tries to fill that gap by providing basic standard definitions and
requirements for DRB protocols, such as Unpredictability, Bias-resistance,
Availability (or Liveness), and Public Verifiability. We classify DRB protocols
according to the nature of interactivity among protocol participants. We also
highlight the most significant features of DRB protocols such as scalability,
complexity, and performance along with a brief discussion on its improvement.
We present future research directions along with a few interesting research
problems.
