Researchers use ultrasonic waves that vibrate through tables to access cell phones
Ultrasonic waves don’t make sound, but they can still activate Siri on your cell phone and make it make calls, take pictures or read text content to a stranger. All this without the knowledge of the owner of the phone.
Ning Zhang, Assistant Professor of Computer Science and Engineering at the McKelvey School of Engineering
Attacks on cell phones are nothing new, and researchers have already shown that ultrasonic waves can be used to deliver a single command in the air.
However, research from the University of Washington in St. Louis broadens the scope of the vulnerability that ultrasonic waves pose to cell phone security. These waves, the researchers found, can propagate through many solid surfaces to activate speech recognition systems and – with the addition of cheap hardware – the person behind the attack can also hear the response. from the phone.
“We want to raise awareness of such a threat,” said Ning Zhang, assistant professor of computer science and engineering at the McKelvey School of Engineering. “I want everyone to know that.”
Zhang and his co-authors were able to send “voice” commands to cell phones as they sat discreetly on a table next to the owner. With the addition of a stealthily placed microphone, researchers were able to communicate back and forth with the phone, ultimately controlling it from afar.
Ultrasonic waves are sound waves whose frequency is higher than what humans can hear and it has a vibrator. However, cell phone microphones can and do record these higher frequencies. “If you know how to play with the signals, you can get the phone in such a way that when it interprets the incoming sound waves, it will think you are saying a command,” Zhang said.
To test the ability of ultrasonic waves to transmit these “commands” through solid surfaces, the research team set up a host of experiments that included a telephone on a table.
A microphone and a piezoelectric transducer (PZT), which is used to convert electricity into ultrasonic waves. On the other side of the phone table, seemingly hidden from the phone user, is a waveform generator to generate the correct signals.
The team ran two tests, one to retrieve an SMS (text) password and one to make a fraudulent call. The first test was based on the common virtual assistant command “read my messages” and the use of two-factor authentication, in which a password is sent to a user’s phone – a bank , for example – to verify the identity of the user.
The attacker first told the virtual assistant to lower the volume to level 3. At this volume, the victim did not notice the responses of his phone in an office with a moderate noise level.
Then, when a simulated message from a bank arrived, the attacking device sent the command “read my messages” to the phone. The response was audible by the microphone under the table, but not by the victim.
In the second test, the attacking device sent the message “Call Sam on the speaker”, initiating a call. Using the microphone under the table, the attacker was able to have a conversation with “Sam”.
The team tested 17 different phone models, including popular iPhone, Galaxy, and Moto models. All but two were vulnerable to ultrasonic wave attack.
Ultrasonic waves passed through metal, glass and wood
They also tested different table surfaces and phone configurations.
“We did it on metal. We did it on glass. We did it on wood, ”said Zhang. They tried to place the phone in different positions, changing the orientation of the microphone. They placed objects on the table in an attempt to dampen the force of the waves. “It always worked,” he said. Even at distances of up to 30 feet.
Ultrasonic wave attacks also worked on plastic tables, but not as reliably.
Phone cases only slightly affected attack success rates. Placing water on the table, potentially to absorb the waves, had no effect. In addition, a wave of attack could affect multiple phones simultaneously.
Zhang said the success of the “surf attack,” as it is called in the newspaper, highlights the less often discussed connection between the cyber and the physical. Often times, the media reports how our devices affect the world we live in: Are our cell phones ruining our eyesight? Do headphones or earphones damage our ears? Who is to blame if an autonomous car causes an accident?
“I feel like we don’t pay enough attention to the physics of our computer systems,” he said. “This is going to be one of the keys to understanding the attacks that are spreading between these two worlds.”
The team suggested defense mechanisms that could protect against such an attack. One idea would be the development of phone software that analyzes the received signal to distinguish between ultrasonic waves and genuine human voices, Zhang said. Changing the layout of mobile phones, such as the location of the microphone, to attenuate or suppress ultrasonic waves could also stop a surf attack.
But Zhang said there is an easy way to protect a phone from ultrasonic waves: interlayer-based defense, which uses a soft, woven fabric to increase the “impedance offset.”
In other words, lay the phone on a tablecloth.