  The training and creation of deep learning model is usually costly, thus it
can be regarded as an intellectual property (IP) of the model creator. However,
malicious users who obtain high-performance models may illegally copy,
redistribute, or abuse the models without permission. To deal with such
security threats, a few deep neural networks (DNN) IP protection methods have
been proposed in recent years. This paper attempts to provide a review of the
existing DNN IP protection works and also an outlook. First, we propose the
first taxonomy for DNN IP protection methods in terms of six attributes:
scenario, mechanism, capacity, type, function, and target models. Then, we
present a survey on existing DNN IP protection works in terms of the above six
attributes, especially focusing on the challenges these methods face, whether
these methods can provide proactive protection, and their resistances to
different levels of attacks. After that, we analyze the potential attacks on
DNN IP protection methods from the aspects of model modifications, evasion
attacks, and active attacks. Besides, a systematic evaluation method for DNN IP
protection methods with respect to basic functional metrics, attack-resistance
metrics, and customized metrics for different application scenarios is given.
Lastly, future research opportunities and challenges on DNN IP protection are
presented.
