Clipboard usage is prevalent in mobile applications nowadays. However, insufficient access control on the clipboard in mobile operating systems exposes its contained data to high risks where one application can read the data, store it locally, or even send it to remote servers. Unfortunately, the literature only has ad-hoc studies in this respect and lacks a comprehensive and systematic study of the entire mobile application ecosystem. Therefore, this paper proposes an automated tool, ClipboardScope+, that leverages the principled static program analysis to uncover the clipboard data usage in mobile applications at scale by defining a usage as a combination of two aspects, i.e., how the clipboard data is validated and where does it go. It defines four primary categories of clipboard data operation, namely spot-on, grand-slam, selective, and cherry-pick, based on the clipboard usage in an application. ClipboardScope+ is evaluated on over1.2 millionmobile applications available on Google Play, spanning the years 2022 and 2023. It uncovered an increase of 5.9% in behaviors of storing and transferring clipboard data over the one-year time, most of which occur automatically in background services. We also conducted a comprehensive case study to characterize different clipboard usages and reveal their privacy issues. Moreover, we uncovered a prevalent programming habit of using theSharedPreferencesobject to store historical data, which can become an unnoticeable privacy leakage channel.

With the growing demand for instant messaging, securing group chats has become a critical concern. While cryptographic approaches are essential for this purpose, they typically require secure and efficient protocols for either group key agreement or group key distribution. Most existing solutions struggle to achieve efficient key updates and seamless integration with real-world systems. To address these limitations, we We present ChatKID, an identity-based group key distribution protocol. At the architectural level, ChatKID employs an asymmetric design to address the resource imbalance between the group owner and group members in group key distribution. At the technical level, it develops a novel polynomial-based key derivation method that drastically improves key update efficiency, while its compliance with the SM9 cryptographic standard enables easy integration with numerous systems. We provide formal analyses of correctness and security, including resilience against five common attacks (e.g., man-in-the-middle, replay), and achieve forward and backward secrecy. Subsequently, we compare ChatKID with recent protocols and demonstrate its significant advantages in both storage and communication overhead. Notably, for group members—typically resource-constrained mobile devices—ChatKID reduces overhead by one to two orders of magnitude (i.e., to$1/10\sim 1/100$) compared to others. Furthermore, we compare ChatKID with mainstream instant messaging applications and demonstrate advantages in terms of connection dependency, computational overhead, communication overhead, and storage requirements. Finally, simulation experiments indicate its superior performance in typical instant messaging scenarios. Taken together, these results suggest that ChatKID holds significant promise for advancing group key distribution in real-world instant messaging applications.

Multi-port chargers, designed to simultaneously charge multiple mobile devices such as smartphones, have gained significant popularity, with millions of units sold in recent years. However, this multi-device charging feature introduces security and privacy risks. If not properly designed and implemented, these chargers can enable communication between connected devices because they are inherently interconnected, which leads to crosstalk voltage leakages. Despite their widespread use, these risks have not been thoroughly investigated. We have identified novel attack surfaces in the circuit design of multi-port chargers that allow an adversary who shares the multi-port charger with the target victim in close proximity to exploit one port to (i) recognize fine-grained user activities of other devices being charged, (ii) eavesdrop on secret audio transmission from USB-C audio pins, and (iii) inject malicious audio commands into built-in voice assistants of charging devices (e.g., Siri, Google Assistant). In this paper, we design and implement XPORTHEFT, a novel system to analyze and demonstrate the uncovered security and privacy threats in multi-port chargers. Specifically, it leverages changes in voltage signals in one neighbor port to monitor voltage changes in the charging port induced by user activities in various user interfaces, such as recognizing running apps and detecting keystrokes. Moreover, XPORTHEFT can also achieve audio transmission eavesdropping and launch inaudible audio injection attacks from the neighbor port to the charging mobile device via the USB-C interface. We extensively evaluate the effectiveness of XPORTHEFT using five commercial multi-port chargers and five mobile devices. The evaluation results show its high effectiveness in recognizing the launch of 20 mobile apps (88.7%) and revealing unlocking passcodes (98.8%), as well as eavesdropping on the audios of numeric digits (97.1%) and alphabetic characters (98.0%). Furthermore, XPORTHEFT achieves 100% success rates in inaudible audio injection attacks on three commercial voice assistants. In addition, our study also shows that XPORTHEFT is resilient to various impact factors and presents the potential to attack multiple victims.