Scientists develop ‘ultrasound-firewall’ for smartphone privacy

This mobile application detects acoustic cookies, brings them to the attention of users and if desired, blocks the tracking.

Scientists have developed the first ultrasound-firewall that can prevent hackers from eavesdropping on hidden data transmission between smartphones and other mobile devices.

The permanent networking of mobile devices can endanger the privacy of users and lead to new forms of monitoring. New technologies such as Google Nearby and Silverpush use ultrasonic sounds to exchange information between devices via loudspeakers and microphones.

More and more of our devices communicate via this inaudible communication channel. Ultrasonic communication allows devices to be paired and information to be exchanged. It also makes it possible to track users and their behaviour over a number of devices, much like cookies on the web. Almost every device with a microphone and a loudspeaker can send and receive ultrasonic sounds. Users are usually unaware of this inaudible and hidden data transmission.

Researchers from the St Polten University of Applied Sciences in Austria has developed a mobile application that detects acoustic cookies, brings them to the attention of users and if desired, blocks the tracking. The app is, in a sense, the first available ultrasound-firewall for smartphones and tablets.

“The most challenging part of developing the app was to devise a method that can detect different existing ultrasound-transmission techniques reliably and in real time,” said Matthias Zeppelzauer, who led the project.

Such ultrasonic signals can be used for so-called “cross-device tracking”. This makes it possible to track the user’s behaviour across multiple devices, and relevant user profiles can be merged with one other. In this way, more accurate user profiles can be created for targeted advertising and filtering of internet content. Unlike their electronic counterparts when visiting web pages, up to now it has not been possible to block acoustic cookies.

“In order to accept voice commands, the mobile phone microphone is often permanently active. Every mobile application that has access to the microphone as well as the operating system itself can at any time without notice: activate the microphone of a mobile device, listen to it, detect acoustic cookies and synchronise it over the Internet,” said Zeppelzauer.

Users are often not informed of this information transmission during ongoing operation. Only a permanent deactivation of the microphone would help, whereby the device as a telephone would become unusable. Researchers developed a procedure to expose the cookies and inform device users. For masking and blocking the ultrasonic data transfer, interference signals are transmitted via the loudspeaker of the mobile device.

Thus, acoustic cookies can be neutralised before operating systems or mobile applications can access them. Users can selectively block cookies without affecting the functionality of the smartphone. The masking of the cookies occurs by means of ultrasound, which is inaudible to humans.

“There is currently no technology on the market that can detect and block acoustic cookies. The application developed in this project represents the first approach that gives people control over this type of tracking,” said Zeppelzauer.