Speech recognition (SR) systems such as Siri or Google Now have become an increasingly popular human-computer interaction method, and have turned various systems into voice controllable systems (VCS). Prior work on attacking VCS shows that the hidden voice commands that are incomprehensible to people can control the systems. Hidden voice commands, though "hidden", are nonetheless audible. In this work, we design a totally inaudible attack, DolphinAttack, that modulates voice commands on ultrasonic carriers (e.g., f > 20 kHz) to achieve inaudibility. By leveraging the nonlinearity of the microphone circuits, the modulated low-frequency audio commands can be successfully demodulated, recovered, and more importantly interpreted by the speech recognition systems. We validated DolphinAttack on popular speech recognition systems, including Siri, Google Now, Samsung S Voice, Huawei HiVoice, Cortana and Alexa. By injecting a sequence of inaudible voice commands, we show a few proof-of-concept attacks, which include activating Siri to initiate a FaceTime call on iPhone, activating Google Now to switch the phone to the airplane mode, and even manipulating the navigation system in an Audi automobile. We propose hardware and software defense solutions, and suggest to re-design voice controllable systems to be resilient to inaudible voice command attacks.

https://dl.acm.org/doi/pdf/10.1145/3133956.3134052

DolphinAttack: Inaudible Voice Commands

We show that the MEMS gyroscopes found on modern smart phones are sufficiently sensitive to measure acoustic signals in the vicinity of the phone. The resulting signals contain only very low-frequency information (<200Hz). Nevertheless we show, using signal processing and machine learning, that this information is sufficient to identify speaker information and even parse speech. Since iOS and Android require no special permissions to access the gyro, our results show that apps and active web content that cannot access the microphone can nevertheless eavesdrop on speech in the vicinity of the phone.

/pdf/gyrophone-recognizing-speech-from-gyroscope-signals-514nfsug55.pdf

Gyrophone: recognizing speech from gyroscope signals

Sensing and actuation systems contain sensors to observe the environment and actuators to influence it. However, these sensors can be tricked by maliciously fabricated physical properties. In this paper, we investigated whether an adversary could incapacitate drones equipped with Micro-Electro-Mechanical Systems (MEMS) gyroscopes using intentional sound noise. While MEMS gyroscopes are known to have resonant frequencies that degrade their accuracy, it is not known whether this property can be exploited maliciously to disrupt the operation of drones.

We first tested 15 kinds of MEMS gyroscopes against sound noise and discovered the resonant frequencies of seven MEMS gyroscopes by scanning the frequencies under 30 kHz using a consumer-grade speaker. The standard deviation of the resonant output from those gyroscopes was dozens of times larger than that of the normal output. After analyzing a target drone's flight control system, we performed real-world experiments and a software simulation to verify the effect of the crafted gyroscope output. Our real-world experiments showed that in all 20 trials, one of two target drones equipped with vulnerable gyroscopes lost control and crashed shortly after we started our attack. A few interesting applications and countermeasures are discussed at the conclusion of this paper.

/pdf/rocking-drones-with-intentional-sound-noise-on-gyroscopic-5dqt3vqge6.pdf

Rocking drones with intentional sound noise on gyroscopic sensors

An underactuated mechanical system (UMS) is a system which has fewer independent control actuators than degrees of freedom to be controlled. Control of UMS is considered as one of the most active fields of research because of its diverse engineering applications. This survey reviews UMS from its history to the state-of-the-art research on modelling, classification, control, and to some extent, provides some unique insights for bottleneck issues and future research directions.

/pdf/a-survey-of-underactuated-mechanical-systems-4tw16vhjoz.pdf

A Survey of Underactuated Mechanical Systems

Cyber-physical systems depend on sensors to make automated decisions. Resonant acoustic injection attacks are already known to cause malfunctions by disabling MEMS-based gyroscopes. However, an open question remains on how to move beyond denial of service attacks to achieve full adversarial control of sensor outputs. Our work investigates how analog acoustic injection attacks can damage the digital integrity of a popular type of sensor: the capacitive MEMS accelerometer. Spoofing such sensors with intentional acoustic interference enables an out-of-spec pathway for attackers to deliver chosen digital values to microprocessors and embedded systems that blindly trust the unvalidated integrity of sensor outputs. Our contributions include (1) modeling the physics of malicious acoustic interference on MEMS accelerometers, (2) discovering the circuit-level security flaws that cause the vulnerabilities by measuring acoustic injection attacks on MEMS accelerometers as well as systems that employ on these sensors, and (3) two software-only defenses that mitigate many of the risks to the integrity of MEMS accelerometer outputs. We characterize two classes of acoustic injection attacks with increasing levels of adversarial control: output biasing and output control. We test these attacks against 20 models of capacitive MEMS accelerometers from 5 different manufacturers. Our experiments find that 75% are vulnerable to output biasing, and 65% are vulnerable to output control. To illustrate end-to-end implications, we show how to inject fake steps into a Fitbit with a $5 speaker. In our self-stimulating attack, we play a malicious music file from a smartphone's speaker to control the on-board MEMS accelerometer trusted by a local app to pilot a toy RC car. In addition to offering hardware design suggestions to eliminate the root causes of insecure amplification and filtering, we introduce two low-cost software defenses that mitigate output biasing attacks: randomized sampling and 180 degree out-of-phase sampling. These software-only approaches mitigate attacks by exploiting the periodic and predictable nature of the malicious acoustic interference signal. Our results call into question the wisdom of allowing microprocessors and embedded systems to blindly trust that hardware abstractions alone will ensure the integrity of sensor outputs.

WALNUT: Waging Doubt on the Integrity of MEMS Accelerometers with Acoustic Injection Attacks

Microelectromechanical systems (MEMS) gyroscopes are typically smaller and less expensive than their macroscale counterparts. For this reason, they are being used in many new applications, including in harsh environments. It has been well documented that the performance of unprotected MEMS gyroscopes can be deleteriously affected by exposure to mechanical shock or high-frequency vibrations. The results of this investigation experimentally demonstrate that MEMS gyroscopes are also susceptible to high-power high-frequency acoustic noise when acoustic energy frequency components are close to the resonating frequency of the gyroscope's proof mass. Additionally, due to microfabrication tolerances and the resulting differences between otherwise identical devices, there can be significant differences in the acoustically sensitive bandwidth between otherwise identical MEMS gyroscopes. This phenomenon is characterized for the ADXRS300 MEMS gyroscope.

A Characterization of the Performance of a MEMS Gyroscope in Acoustically Harsh Environments

In the fall quarter of 1997, the Auburn University Electrical Engineering Department (USA) implemented a new, interdisciplinary core laboratory sequence. This new laboratory sequence was one outcome of a complete curriculum revision based on four years of work by the departmental Curriculum Study Committee. This paper presents the laboratory curriculum design, and the results of a multi-part assessment conducted beginning one year after implementation. Many students are initially surprised by the level of challenge provided in the first laboratory course, but readily accommodate as they progress through the sequence. A multifaceted assessment strategy has evolved which uses end-of-term student evaluations, retrospective student evaluations, student oral interviews, and faculty interviews. The assessment information is used to improve the laboratories through modification of the laboratory manuals, better instructions to graduate teaching assistants, modifications of experiments, and a purposeful effort to keep all faculty informed of laboratory course content so they can build upon the laboratory experience in classroom teaching. The overall result of the new laboratory experience is that students have a more integrated approach to design and a much better understanding of the hardware, software and instrumentation used in electrical engineering practice. In addition, students who complete the sequence have better oral and written communication skills, and are more confident in approaching job interviews and initial job challenges.

An interdisciplinary laboratory sequence in electrical and computer engineering: curriculum design and assessment results

In this paper, three techniques for robust control of underactuated robots are experimentally compared on the classical ball and beam system. An adaptive tracking controller is first designed and implemented to identify the nominal friction characteristic. Then, designs for a linear quadratic regulator (LQR), subspace stabilization controller, and combined error metric controller are presented. Step response tests confirm that both nonlinear approaches exhibit better stability properties than the standard LQR design. In addition, the subspace stabilization approach permits a much more aggressive beam motion, resulting in shorter settling time with excellent control of overshoot.

Underactuated Robot Control: Comparing LQR, Subspace Stabilization, and Combined Error Metric Approaches

Many microelectromechanical systems (MEMS) devices possess charged capacitor structures where the suspension system allows relative electrode motion due to internal or external stimuli. When such a device is subjected to external mechanical vibrations present in a harsh operating environment, unwanted movement between the capacitor plates can generate a noise current which is injected into the connected circuitry. This paper analyzes this phenomenon and presents a model for the dynamics of a MEMS device with capacitive plates experiencing relative motion due to external stimuli. A Fourier series expansion of the current is developed to characterize the frequency content of the signal in closed form for a given vibration frequency, and simulation and experimental results are presented.

Electrical Noise in MEMS Capacitive Elements Resulting From Environmental Mechanical Vibrations in Harsh Environments

Applications exist for microelectromechanical systems (MEMS) devices where the measurement or estimation of the relative velocity, or at least the direction of instantaneous relative velocity, between two microstructures in normal translational motion is required. A technique for directly measuring the relative velocity has not been available. This paper presents a technique for directly measuring the relative velocity between two microstructures in normal translational motion. The technique consists of measuring the current flowing into the capacitance formed between the two microstructures when a constant voltage is applied across them. The technique and the resulting nonlinear distortion in the velocity measurement are characterized. A prototype relative velocity sensor is fabricated and evaluated to verify the measurement technique

Characterization and Experimental Verification of the Nonlinear Distortion in a Technique for Measuring the Relative Velocity Between Micromachined Structures in Normal Translational Motion

A.S. Hodel

Papers

A Characterization of the Performance of a MEMS Gyroscope in Acoustically Harsh Environments

An interdisciplinary laboratory sequence in electrical and computer engineering: curriculum design and assessment results

Underactuated Robot Control: Comparing LQR, Subspace Stabilization, and Combined Error Metric Approaches

Electrical Noise in MEMS Capacitive Elements Resulting From Environmental Mechanical Vibrations in Harsh Environments

Characterization and Experimental Verification of the Nonlinear Distortion in a Technique for Measuring the Relative Velocity Between Micromachined Structures in Normal Translational Motion