  The commercial use of Machine Learning (ML) is spreading; at the same time,
ML models are becoming more complex and more expensive to train, which makes
Intellectual Property Protection (IPP) of trained models a pressing issue.
Unlike other domains that can build on a solid understanding of the threats,
attacks and defenses available to protect their IP, the ML-related research in
this regard is still very fragmented. This is also due to a missing unified
view as well as a common taxonomy of these aspects.
  In this paper, we systematize our findings on IPP in ML, while focusing on
threats and attacks identified and defenses proposed at the time of writing. We
develop a comprehensive threat model for IP in ML, categorizing attacks and
defenses within a unified and consolidated taxonomy, thus bridging research
from both the ML and security communities.
