Blas Kojusner

Yan Long, Pirouz Naghavi, Blas Kojusner et al.

Our research discovers how the rolling shutter and movable lens structures widely found in smartphone cameras modulate structure-borne sounds onto camera images, creating a point-of-view (POV) optical-acoustic side channel for acoustic eavesdropping. The movement of smartphone camera hardware leaks acoustic information because images unwittingly modulate ambient sound as imperceptible distortions. Our experiments find that the side channel is further amplified by intrinsic behaviors of Complementary metal-oxide-semiconductor (CMOS) rolling shutters and movable lenses such as in Optical Image Stabilization (OIS) and Auto Focus (AF). Our paper characterizes the limits of acoustic information leakage caused by structure-borne sound that perturbs the POV of smartphone cameras. In contrast with traditional optical-acoustic eavesdropping on vibrating objects, this side channel requires no line of sight and no object within the camera's field of view (images of a ceiling suffice). Our experiments test the limits of this side channel with a novel signal processing pipeline that extracts and recognizes the leaked acoustic information. Our evaluation with 10 smartphones on a spoken digit dataset reports 80.66%, 91.28%, and 99.67% accuracies on recognizing 10 spoken digits, 20 speakers, and 2 genders respectively. We further systematically discuss the possible defense strategies and implementations. By modeling, measuring, and demonstrating the limits of acoustic eavesdropping from smartphone camera image streams, our contributions explain the physics-based causality and possible ways to reduce the threat on current and future devices.

Muhammad Sajidur Rahman, Blas Kojusner, Ryon Kennedy et al.

Frequently advised secure development recommendations often fall short in practice for app developers. Tool-driven (e.g., using static analysis tools) approaches lack context and domain-specific requirements of an app being tested. App developers struggle to find an actionable and prioritized list of vulnerabilities from a laundry list of security warnings reported by static analysis tools. Process-driven (e.g., applying threat modeling methods) approaches require substantial resources (e.g., security testing team, budget) and security expertise, which small to medium-scale app dev teams could barely afford. To help app developers securing their apps, we propose SO{U}RCERER, a guiding framework for Android app developers for security testing. SO{U}RCERER guides developers to identify domain-specific assets of an app, detect and prioritize vulnerabilities, and mitigate those vulnerabilities based on secure development guidelines. We evaluated SO{U}RCERER with a case study on analyzing and testing 36 Android mobile money apps. We found that by following activities guided by SO{U}RCERER, an app developer could get a concise and actionable list of vulnerabilities (24-61% fewer security warnings produced by SO{U}RCERER than a standalone static analyzer), directly affecting a mobile money app's critical assets, and devise a mitigation plan. Our findings from this preliminary study indicate a viable approach to Android app security testing without being overwhelmingly complex for app developers.