Secure and Fast Decision Tree Evaluation on Outsourced Cloud Data

Decision trees are famous machine learning classifiers which have been widely used in many areas, such as healthcare, text classification and remote diagnostics, etc. The service providers usually host a decision tree model on the cloud server and provide some classification service for clients to use such a model remotely. In such a scenario, the model is a valuable asset to the cloud which should not be disclosed to the clients, while the query data and classification results are private to the client. To solve such a problem, we propose several building blocks, i.e., secure comparison and secure polynomial calculation, in a two-cloud model. Based on these building blocks, we design a privacy-preserving decision tree evaluation scheme. Compared with the most recent works, our scheme can fully protect the tree model and clients' data privacy simultaneously. Besides, our scheme also supports offline service users which is essential to the system's scalability. Moreover, through theoretical analysis and real-world experimental test, it is oblivious that our scheme is quite efficient.