Paul Staat

Johannes Kortz, Paul Staat, Christof Paar et al.

Wi-Fi signals can be exploited by adversaries as a sensing side channel to eavesdrop on physical information. By monitoring propagation effects of radio waves within the victim's environment, attackers can remotely infer sensitive information. One particularly concerning example is PIN code inference, where the attacker faces the challenge of mapping Wi-Fi physical-layer channel estimations back into typed digits. While effective in their training environment, such attacks typically fail as soon as they are deployed in unseen environments. The current state-of-the-art attack, WiKI-Eve, attempts to overcome this problem using a deep-learning approach, reporting high PIN code inference accuracy independent of environments, devices, and users. While this suggests a significant real-world threat, it is not well understood how far the attack actually reaches, nor what its underlying generalization performance is based on. In this work, we close this gap by presenting PINSIGHT, a novel methodology that separates the effects of environmental variation and PIN code typing. This enables the first rigorous threat assessment of such attacks, evaluating their generalization capabilities and limitations. Our approach leverages a robotic typing platform that produces highly repeatable keystroke events across systematically varied environment changes [...]. This dataset constitutes the first benchmark for environment generalization in Wi-Fi PIN code inference attacks. Evaluating several state-of-the-art methods, we find that attacks generalize reliably across changes in the surrounding environment but degrade substantially when the channel's encoding of typing itself shifts - precisely the condition that defines a realistic attack scenario. We conclude that the reported performance of current state-of-the-art Wi-Fi PIN inference attacks is not representative of the actual real-world threat.

Paul Staat, Daniel Davidovich, Christof Paar

Physical isolation from external networks - an airgap - aims to minimize exposure to remote attacks. Yet capable adversaries still achieve code execution on air-gapped systems, and prior work has shown that they can then wirelessly exfiltrate data via unintended emissions. In this work, we demonstrate the reverse direction: malicious code on an embedded device enables wireless infiltration of air-gapped systems, granting attackers command-and-control over compromised targets. Leveraging physical effects previously studied in the context of electromagnetic interference (EMI), we show that parasitic radio frequency (RF) sensitivity in printed circuit board (PCB) traces and on-chip analog-to-digital converters (ADCs) turns commodity embedded devices into inadvertent radio receivers. Unlike prior infiltration techniques, our approach requires no dedicated sensors (e.g., microphones, LEDs, or temperature sensors) and works in non-line-of-sight scenarios. In our evaluation, an ordinary microcontroller evaluation board reliably recovers communication signals from tens of meters at data rates of up to 100 kbps. Applying a systematic methodology to discover such device-intrinsic RF sensitivity, we evaluate twelve commercial embedded devices and two custom prototypes, finding that all exhibit reception capabilities in the 300-1000 MHz range. Our findings challenge the assumption that embedded devices without radios lack an inbound radio paths and call for air-gap threat models that account for both emission-based leakage and unintended reception.

Paul Staat, Kai Jansen, Christian Zenger et al.

Today, we use smartphones as multi-purpose devices that communicate with their environment to implement context-aware services, including asset tracking, indoor localization, contact tracing, or access control. As a de-facto standard, Bluetooth is available in virtually every smartphone to provide short-range wireless communication. Importantly, many Bluetooth-driven applications such as Phone as a Key (PaaK) for vehicles and buildings require proximity of legitimate devices, which must be protected against unauthorized access. In earlier access control systems, attackers were able to violate proximity-verification through relay station attacks. However, the vulnerability of Bluetooth against such attacks was yet unclear as existing relay attack strategies are not applicable or can be defeated through wireless distance measurement. In this paper, we design and implement an analog physical-layer relay attack based on low-cost off-the-shelf radio hardware to simultaneously increase the wireless communication range and manipulate distance measurements. Using our setup, we successfully demonstrate relay attacks against Bluetooth-based access control of a car and a smart lock. Further, we show that our attack can arbitrarily manipulate Multi-Carrier Phase-based Ranging (MCPR) while relaying signals over 90 m.

Paul Staat, Johannes Tobisch, Christian Zenger et al.

A whole range of attacks becomes possible when adversaries gain physical access to computing systems that process or contain sensitive data. Examples include side-channel analysis, bus probing, device cloning, or implanting hardware Trojans. Defending against these kinds of attacks is considered a challenging endeavor, requiring anti-tamper solutions to monitor the physical environment of the system. Current solutions range from simple switches, which detect if a case is opened, to meshes of conducting material that provide more fine-grained detection of integrity violations. However, these solutions suffer from an intricate trade-off between physical security on the one side and reliability, cost, and difficulty to manufacture on the other. In this work, we demonstrate that radio wave propagation in an enclosed system of complex geometry is sensitive against adversarial physical manipulation. We present an anti-tamper radio (ATR) solution as a method for tamper detection, which combines high detection sensitivity and reliability with ease-of-use. ATR constantly monitors the wireless signal propagation behavior within the boundaries of a metal case. Tamper attempts such as insertion of foreign objects, will alter the observed radio signal response, subsequently raising an alarm. The ATR principle is applicable in many computing systems that require physical security such as servers, ATMs, and smart meters. As a case study, we use 19" servers and thoroughly investigate capabilities and limits of the ATR. Using a custom-built automated probing station, we simulate probing attacks by inserting needles with high precision into protected environments. Our experimental results show that our ATR implementation can detect 16 mm insertions of needles of diameter as low as 0.1 mm under ideal conditions. In the more realistic environment of a running 19" server, we demonstrate reliable [...]

Paul Staat, Simon Mulzer, Stefan Roth et al.

Wireless radio channels are known to contain information about the surrounding propagation environment, which can be extracted using established wireless sensing methods. Thus, today's ubiquitous wireless devices are attractive targets for passive eavesdroppers to launch reconnaissance attacks. In particular, by overhearing standard communication signals, eavesdroppers obtain estimations of wireless channels which can give away sensitive information about indoor environments. For instance, by applying simple statistical methods, adversaries can infer human motion from wireless channel observations, allowing to remotely monitor premises of victims. In this work, building on the advent of intelligent reflecting surfaces (IRSs), we propose IRShield as a novel countermeasure against adversarial wireless sensing. IRShield is designed as a plug-and-play privacy-preserving extension to existing wireless networks. At the core of IRShield, we design an IRS configuration algorithm to obfuscate wireless channels. We validate the effectiveness with extensive experimental evaluations. In a state-of-the-art human motion detection attack using off-the-shelf Wi-Fi devices, IRShield lowered detection rates to 5% or less.

Paul Staat, Harald Elders-Boll, Markus Heinrichs et al.

The intelligent reflecting surface (IRS) is a promising new paradigm in wireless communications for meeting the growing connectivity demands in next-generation mobile networks. IRS, also known as software-controlled metasurfaces, consist of an array of adjustable radio wave reflectors, enabling smart radio environments, e.g., for enhancing the signal-to-noise ratio (SNR) and spatial diversity of wireless channels. Research on IRS to date has been largely focused on constructive applications. In this work, we demonstrate for the first time that the IRS provides a practical low-cost toolkit for attackers to easily perform complex signal manipulation attacks on the physical layer in real time. We introduce the environment reconfiguration attack (ERA) as a novel class of jamming attacks in wireless radio networks. Here, an adversary leverages the IRS to rapidly vary the electromagnetic propagation environment to disturb legitimate receivers. The IRS gives the adversary a key advantage over traditional jamming: It no longer has to actively emit jamming signals, instead the IRS reflects existing legitimate signals. In addition, the adversary doesn't need any knowledge about the legitimate channel. We thoroughly investigate the ERA in wireless systems based on the widely employed orthogonal frequency division multiplexing (OFDM) modulation. We present insights into the attack through analytical analysis, simulations, as well as experiments. Our results show that the ERA allows to severely degrade the available data rates even with reasonably small IRS sizes. Finally, we implement an attacker setup and demonstrate a practical ERA to slow down an entire Wi-Fi network.

Paul Staat, Harald Elders-Boll, Markus Heinrichs et al.

Physical layer key generation is a promising candidate for cryptographic key establishment between two wireless communication parties. It offers information-theoretic security and is an attractive alternative to public-key techniques. Here, the inherent randomness of wireless radio channels is used as a shared entropy source to generate cryptographic key material. However, practical implementations often suffer from static channel conditions which exhibit a limited amount of randomness. In the past, considerable research efforts have been made to address this fundamental limitation. However, current solutions are not generic or require dedicated hardware extensions such as reconfigurable antennas. In this paper, we propose a novel wireless key generation architecture based on randomized channel responses from an intelligent reflecting surface (IRS). Due to its passive nature, a cooperative IRS is well-suited to provide randomness for conventional resource-constrained radios. We conduct the first practical studies to successfully demonstrate IRS-based physical-layer key generation with an OFDM system. In a static environment, using a single subcarrier only, our IRS-assisted prototype system achieves a key generation rate (KGR) of 97.39 bps with 6.5% key disagreement rate (KDR) after quantization, while passing standard randomness tests.