Benjamin Semal

Carlton Shepherd, Jan Kalbantner, Benjamin Semal et al.

Mobile devices often distribute measurements from physical sensors to multiple applications using software multiplexing. On Android devices, the highest requested sampling frequency is returned to all applications, even if others request measurements at lower frequencies. In this paper, we comprehensively demonstrate that this design choice exposes practically exploitable side-channels using frequency-key shifting. By carefully modulating sensor sampling frequencies in software, we show how unprivileged malicious applications can construct reliable spectral covert channels that bypass existing security mechanisms. Additionally, we present a novel variant that allows an unprivileged malicious application to profile other active, sensor-enabled applications at a coarse-grained level. Both methods do not impose any special assumptions beyond accessing standard mobile services available to developers. As such, our work reports side-channel vulnerabilities that exploit subtle yet insecure design choices in Android sensor stacks.

J. Kalbantner, K. Markantonakis, D. Hurley-Smith et al.

Distributed Ledger Technology (DLT) has an enormous potential but also downsides. One downside of many DLT systems, such as blockchain, is their limited transaction throughput that hinders their adoption in many use cases (e.g., real-time payments). State channels have emerged as a potential solution to enhance throughput by allowing transactions to process off-chain. While current proposals can increase scalability, they require high collateral and lack support for dynamic systems that require asynchronous state transitions. Additionally, the latency of channel initialisations can cause issues especially if fast interactions are required. In this paper, we propose an atomic, scalable and privacy-preserving protocol that enables secure and dynamic updates. We develop a smart contract-based Credit-Note System (CNS) that allows participants to lock funds before a state channel initialisation, which enhances flexibility and efficiency. We formalise our model using the Universal Composability (UC) framework and demonstrate that it achieves the stated design goals of privacy, scalability, and atomicity. Moreover, we implement a dispute process in the state channel to counter availability attacks. Finally, we analyse the protocol in the context of an asynchronous smart grid-based marketplace.