Cloud vendors are increasingly offering machine learning services as part of
their platform and services portfolios. These services enable the deployment of
machine learning models on the cloud that are offered on a pay-per-query basis
to application developers and end users. However recent work has shown that the
hosted models are susceptible to extraction attacks. Adversaries may launch
queries to steal the model and compromise future query payments or privacy of
the training data. In this work, we present a cloud-based extraction monitor
that can quantify the extraction status of models by observing the query and
response streams of both individual and colluding adversarial users. We present
a novel technique that uses information gain to measure the model learning rate
by users with increasing number of queries. Additionally, we present an
alternate technique that maintains intelligent query summaries to measure the
learning rate relative to the coverage of the input feature space in the
presence of collusion. Both these approaches have low computational overhead
and can easily be offered as services to model owners to warn them of possible
extraction attacks from adversaries. We present performance results for these
approaches for decision tree models deployed on BigML MLaaS platform, using
open source datasets and different adversarial attack strategies.

该研究提出了一种基于云的提取监视器，通过观察单个和串通的对手用户的查询和响应流来量化模型的提取状态，从而使用信息增益来测量具有不断增加查询数量的用户的模型学习速率，并维护智能查询摘要以在串通存在的情况下测量与输入特征空间覆盖度相关的学习速率，以提醒模型所有者可能存在侵犯攻击。