This study addresses the privacy problems of data provided by multiple data owners for range query processing on the cloud. Although existing methods preserve data privacy against the cloud or data analysts who receive query responses, protecting data privacy from both remains a challenge. Combining differential privacy (DP) and homomorphic encryption (HE) to construct differentially private outputs over encrypted raw data is a promising way to avoid data privacy leakage to the cloud with encryption while protecting data privacy from data analysts with DP. Although DP adopts several partitioning algorithms to achieve small noise, partitioning cannot be executed once the data is encrypted. In this paper, we propose a new HE-friendly privacy-preserving partitioning algorithm satisfying DP. Although HE enables operations over encrypted data, the execution time of such primitive arithmetic operations is approximately 109times slower than without encryption. Therefore, it is mandatory to reduce the calculation complexity. The proposed partitioning method, which only compares every next-to-each-other data to merge, achieves $\mathcal{O}\left( n \right)$ calculation complexity, where n is the domain size of the input histograms, whereas the greedy algorithm requires $\mathcal{O}\left( {{2^n}} \right)$. The experimental evaluation showed that the execution time of the proposed algorithm for 4,096-domain-size data was approximately 4 h and 35 min, which was acceptable when creating a data summary for the range query processing system and not targeting on-the-fly adoption of DP. Additionally, we confirmed that the accuracy of the proposed algorithm was equivalent to that of the state-of-the-art partitioning algorithm.

Recently, it is shown that shuffling can amplify the central differential privacy guarantees of data randomized with local differential privacy. Within this setup, a centralized, trusted shuffler is responsible for shuffling by keeping the identities of data anonymous, which subsequently leads to stronger privacy guarantees for systems. However, introducing a centralized entity to the originally local privacy model loses some appeals of not having any centralized entity as in local differential privacy. Moreover, implementing a shuffler in a reliable way is not trivial due to known security issues and/or requirements of advanced hardware or secure computation technology.

How can we explore the unknown properties of high-dimensional sensitive relational data while preserving privacy? We study how to construct an explorable privacy-preserving materialized view under differential privacy. No existing state-of-the-art methods simultaneously satisfy the following essential properties in data exploration: workload independence, analytical reliability (i.e., providing error bound for each search query), applicability to high-dimensional data, and space efficiency. To solve the above issues, we propose HDPView, which creates a differentially private materialized view by well-designed recursive bisected partitioning on an original data cube, i.e., count tensor. Our method searches for block partitioning to minimize the error for the counting query, in addition to randomizing the convergence, by choosing the effective cutting points in a differentially private way, resulting in a less noisy and compact view. Furthermore, we ensure formal privacy guarantee and analytical reliability by providing the error bound for arbitrary counting queries on the materialized views. HDPView has the following desirable properties: (a) Workload independence , (b) Analytical reliability , (c) Noise resistance on high-dimensional data , (d) Space efficiency. To demonstrate the above properties and the suitability for data exploration, we conduct extensive experiments with eight types of range counting queries on eight real datasets. HDPView outperforms the state-of-the-art methods in these evaluations.

How can we release a massive volume of sensitive data while mitigating privacy risks? Privacy-preserving data synthesis enables the data holder to outsource analytical tasks to an untrusted third party. The state-of-the-art approach for this problem is to build a generative model under differential privacy, which offers a rigorous privacy guarantee. However, the existing method cannot adequately handle high dimensional data. In particular, when the input dataset contains a large number of features, the existing techniques require injecting a prohibitive amount of noise to satisfy differential privacy, which results in the outsourced data analysis meaningless. To address the above issue, this paper proposes privacy-preserving phased generative model (P3GM), which is a differentially private generative model for releasing such sensitive data. P3GM employs the two-phase learning process to make it robust against the noise, and to increase learning efficiency (e.g., easy to converge). We give theoretical analyses about the learning complexity and privacy loss in P3GM. We further experimentally evaluate our proposed method and demonstrate that P3GM significantly outperforms existing solutions. Compared with the state-of-the-art methods, our generated samples look fewer noises and closer to the original data in terms of data diversity. Besides, in several data mining tasks with synthesized data, our model outperforms the competitors in terms of accuracy.

Graph convolutional neural networks, which learn aggregations over neighbor nodes, have achieved great performance in node classification tasks. However, recent studies reported that such graph convolutional node classifier can be deceived by adversarial perturbations on graphs. Abusing graph convolutions, a node's classification result can be influenced by poisoning its neighbors. Given an attributed graph and a node classifier, how can we evaluate robustness against such indirect adversarial attacks? Can we generate strong adversarial perturbations which are effective on not only one-hop neighbors, but more far from the target? In this paper, we demonstrate that the node classifier can be deceived with high-confidence by poisoning just a single node even two-hops or more far from the target. Towards achieving the attack, we propose a new approach which searches smaller perturbations on just a single node far from the target. In our experiments, our proposed method shows 99% attack success rate within two-hops from the target in two datasets. We also demonstrate that m-layer graph convolutional neural networks have chance to be deceived by our indirect attack within m-hop neighbors. The proposed attack can be used as a benchmark in future defense attempts to develop graph convolutional neural networks with having adversary robustness.

Given a collection of seasonal time-series, how can we find regular (cyclic) patterns and outliers (i.e. rare events)? These two types of patterns are hidden and mixed in the time-varying activities. How can we robustly separate regular patterns and outliers, without requiring any prior information?

This paper proposes a continuous anonymization method for a trajectory stream. In today's mobile environment, positions of moving objects are frequently sensed and collected. For real-time movement pattern analyses of people and automobiles, trajectory streams have attracted a lot of attention. Trajectory streams lead to sensitive locations, such as homes and personal hospitals. Additionally, a set of spatio-temporal data might identify a user from a trajectory stream. Therefore, publishing original trajectory streams may cause critical breaches of privacy. To protect privacy of users, we need a mechanism which makes it difficult to identify users from crowds of trajectory streams. Several techniques for anonymizing trajectories have been proposed. Anonymized trajectories can be published without concerning about privacy issues. However, for the continuous publishing of trajectory streams, existing trajectory anonymization methods are not suitable because they anonymize the overall trajectories at a time. If the existing methods are applied in the continuous publishing, the resolution of anonymized trajectory is hugely degraded or trace-ability is lost. In this paper, we propose an anonymization technique for a trajectory stream. The method continuously anonymizes trajectory streams one by one, and dynamically reforms anonymized trajectory streams to improve the resolution. The experiments showed that our method could keep the resolution at a constant level.

With the recent flood of information, trust in that information is gaining a lot of attention in determining how information is used. Social bookmarking is a new information sharing service that allows individuals to bookmark and annotate web pages of interest or those that impress them. It is attracting attention and growing in popularity. In social bookmark services, users' bookmarks and annotations given by tags are informative indicators of user interest in web pages. This paper proposes a method to evaluate the trust and significance of web pages based on social bookmarks. Extending the HITS approach, we regard web pages as Authority and users as Hubs and evaluate trust and significance values of web pages. We show usefulness of the proposed approach through experiments.