Motion sensors to intercept telephone conversations, one possible scenario!

A group of university researchers has developed an example of an eavesdropping attack targeting Android devices which allows you to recognize the gender and identity of the caller and to be able to intercept even private voice communications, using data from motion sensors when triggered by vibrations generated by mobile device speakers.

EarSpy, this is the name of the technique, retraces academic exercises already attempted in the past albeit with less success, both due to insufficient vibrations of the loudspeakers and due to a lower sensitivity of the motion sensors. However, evolution and progress have changed the cards on the table, allowing for the creation of smartphones with better performing speakers and more precise sensors: a combination that allows new attempts to be given more chances.

In their experiments the researchers used a OnePlus 7T and a OnePlus 9 and various sets of pre-recorded audio played through the two devices’ speakers only. The data that the accelerometer generated during a fake call was collected by the third-party app Physics Toolbox Sensor Suite and fed to MATLAB extension. A machine learning algorithm suitably trained with datasets was then used to recognize the vocal content, the identity of the caller and the gender.

The researchers achieved relatively high success rates in all three fields, with the variability depending on the data set used and the device. In general, however, observe the researchers, the elements that influence the final result are the loudspeaker volume, the arrangement of the internal components and the physical construction of the device: all together they contribute to determining the diffusion of the reverberation and, therefore, the vibrations collected by the motion sensors. Movements of the user or vibrations of the surrounding environment can also reduce the accuracy of the collected data.

EarSpy therefore a proof of concept, rather than a real possibility of interception: the researchers suggest that smartphone manufacturers also take these aspects into consideration in the design work so as to create devices in such a way that the motion sensors have no way of accurately collecting the internal vibrations generated by the speakers. Currently the devices that are equipped with Android 13 do not allow to record vibrations at frequencies higher than 200Hz, but the interceptions would still be possible, albeit with a lower accuracy.