Speaking of hacker attacks, most people will first think of software and network communications level of invasion, few people will notice that the hardware sensor will be attacked, even more unexpected is the attack path turned out to be ubiquitous 'sound wave.' However, a recent study by the University of Michigan, USA, successfully exploited acoustic waves Sensor to attack the acceleration sensor and successfully invaded the smartphone and smart wearable device Fitbit bracelet. Mainly analog acoustics attack capacitive MEMS acceleration sensor, by deliberately creating interference to achieve the purpose of deceptive sensors. Microprocessors and embedded systems are often 'blindly trusted' the output of these sensors, so that attackers can take the opportunity to artificially for the microprocessor and embedded systems selectively enter some values.

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First, the physical modeling, mainly for the MEMS acceleration sensor malicious acoustic interference. Second, the circuit defect research, it is because of circuit defects, so MEMS acceleration sensors and systems for acoustic intrusion attacks, there will be security vulnerabilities. Third, two software defense methods to reduce the safety risk of MEMS acceleration sensors. Kevin Fu, associate professor Suction Control Valve of computer science and engineering at the University of Michigan, led the study, using teams of precise tuned tones to deceive different types of acceleration sensors. This kind of deceptive attack has become a back door into these devices, so that an attacker can use it to attack the device.

For this study, the professor's research overturned the general assumption about underlying hardware. If you stand in the computer science perspective, you will not find this security problem. If you stand in the material science point of view, you will not find this security problem. You will only find these security holes from the standpoint Fuel Rail Pressure Sensor of computer science and materials science. The attack is a sonic wave, the attack object is the acceleration sensor.
 
  Acceleration sensor is a sensor that can measure the speed of objects in three-dimensional space. Usually by the mass block, dampers, elastic components, sensitive components and appropriate circuit and other components. According to the different sensor sensors, the common acceleration sensor, including capacitive, inductive, strain, piezoresistive, piezoelectric and so on. Acceleration sensors are widely used in automotive electronics, aerospace, medical electronics, unmanned aerial vehicles, smart phones, intelligent hardware, networking Temperature Sensor and other industrial and consumer electronics. It can collect the object's acceleration data information, sent to the chip and embedded systems for analysis and decision-making. Its use includes aircraft navigation, game control, handle vibration and shaking, car brake start detection, seismic testing, engineering vibration, geological exploration, vibration testing and analysis, security and so on.


  Capacitive MEMS acceleration sensor, in the acceleration process, through the perception of mass deviation to measure the acceleration value. When subjected to acceleration, the perceived quality changes, causing the capacitance to change and then converted into an analog voltage signal. The voltage signal can represent the perceived acceleration. Acoustic pressure waves can have an effect on objects on their propagation path. At the resonant frequency, the elastic structure of perceived mass is affected by acoustic disturbances, replacing the original mass perception, resulting in false acceleration signals. This process is somewhat similar to the singer in the singing process, the sound of the sound shattered glass, which is also ABS Sensor a resonance phenomenon. This deceptive acceleration signal is related to the acoustic interference signal, and the resonant frequency of the elastic structure is related to its physical design characteristics, and the resonant frequency of the acoustic disturbance must match the resonant frequency of the elastic structure, thus successfully creating this false acceleration. Therefore, the acoustic attack scheme for MEMS accelerometers is simple: if a system or device uses this MEMS sensor with a security vulnerability to automate state change decisions, then an attacker is likely to exploit this vulnerability to attack.