Location-based augmented reality (LB-AR) applications, such as Pokemon Go, rely on sub-second GPS updates to deliver responsive and immersive user experiences. However, this high-frequency location reporting introduces serious privacy risks. Unlike traditional Location-Based Services (LBS), LB-AR demands real-time protection under strict latency and quality-of-service (QoS) constraints, while providing strong per-location and trajectory-level privacy guarantees. Existing privacy mechanisms struggle to satisfy these requirements: they either introduce prohibitive latency, significantly degrade application utility, or fail to defend against trajectory inference attacks. To address this challenge, we present PrivAR, the first client-side privacy framework for real-time LB-AR. PrivAR introduces two lightweight mechanisms: (i) Planar Staircase Mechanism (PSM), which uses a staircase-shaped distribution to generate noisy locations with strong per-location privacy, low expected distortion, and minimal computational overhead; and (ii) Planar Staircase Mechanism with Intermediate (PSM-I), an extension of PSM that generates a device-resident intermediate trajectory and selectively reuses previously perturbed outputs when insufficient drift is observed, thereby strengthening trace-level privacy while preserving high QoS. We provide theoretical analysis, extensive evaluation on two public mobility datasets and our GeoTrace dataset, and validate PrivAR in a Pokemon GO-style Android prototype. Results show that PrivAR improves AR QoS (game score) by up to 50% and increases attacker Bayes risk by up to 1.8x, while incurring only 0.06 ms of per-update overhead (less than 0.2% of end-to-end latency).

Large-scale data collection, from national censuses to IoT-enabled smart homes, routinely gathers dozens of attributes per individual. These multi-attribute datasets are crucial for analytics but pose significant privacy risks. Local Differential Privacy (LDP) is a powerful tool for protecting user privacy by allowing users to locally perturb their records before releasing them to an untrusted data aggregator. However, existing LDP mechanisms either split the privacy budget across all attributes or treat each attribute independently, thereby ignoring natural inter-attribute correlations. This leads to excessive noise and, consequently, significant utility loss, particularly in high-dimensional datasets. We introduce a two-phase LDP framework that overcomes these limitations by privately learning and exploiting inter-attribute dependencies. In Phase I, a small subset of users applies a standard per-attribute LDP mechanism, enabling the aggregator to derive dependency information from the privatized data. In Phase II, each remaining user perturbs a single randomly chosen attribute with the full privacy budget, while the unreported attributes are reconstructed using Phase~I statistics, incurring no additional privacy cost. As a concrete instantiation, we develop Correlated Randomized Response (Corr-RR), which employs correlation-aware probabilistic mappings to substantially improve estimation accuracy. We prove that Corr-RR satisfies ε-LDP, and demonstrate through extensive experiments on synthetic and real-world datasets that it consistently outperforms state-of-the-art baselines, with the largest gains in high-dimensional and strongly correlated datasets.

Local Differential Privacy (LDP) has been widely recognized as a powerful tool for providing a strong theoretical guarantee of data privacy to data contributors against an untrusted data collector. Under a typical LDP scheme, each data contributor independently randomly perturbs their data before submitting them to the data collector, which in turn infers valuable statistics about the original data from received perturbed data. Common to existing LDP mechanisms is an inherent trade-off between the level of privacy protection and data utility in the sense that strong data privacy often comes at the cost of reduced data utility. Frequency estimation based on Randomized Response (RR) is a fundamental building block of many LDP mechanisms. In this paper, we propose a novel Joint Randomized Response (JRR) mechanism based on correlated data perturbations to achieve locally differentially private frequency estimation. JRR divides data contributors into disjoint groups of two members and lets those in the same group jointly perturb their binary data to improve frequency-estimation accuracy and achieve the same level of data privacy by hiding the group membership information in contrast to the classical RR mechanism. Theoretical analysis and detailed simulation studies using both real and synthetic datasets show that JRR achieves the same level of data privacy as the classical RR mechanism while improving the frequency-estimation accuracy in the overwhelming majority of the cases by up to two orders of magnitude.

Quantification of information leakage is crucial, especially for privacy-preserving systems such as location-based services (LBS) with integrated privacy mechanisms. Existing quantification mainly utilized two approaches: i) the white-box approach, precise but impractical for complex systems, and ii) the black-box approach, practical but struggles with scalability for large output spaces. Recently, Machine Learning (ML) algorithms have been integrated into the black-box approach to effectively approximate information leakage for independent observations with better scalability. However, this method does not provide precise estimates for dependent observations. Intuitively, once a correlated secret is discovered, it becomes easier for an attacker to predict related secrets, leading to an underestimation of information leakage. This paper introduces an ML-based black-box approach to improve the accuracy of information leakage estimation for systems with correlated data, particularly in trace-based scenarios. Our solution uses an ML model for rough estimation and leverages data correlations to refine inferences for more accurate quantification. Evaluation results from three real-world datasets and one collected dataset confirm our solution's effectiveness in accurately and cost-effectively quantifying system leakage for correlated observations.