“Inaudible frequencies”: a firewall appeared blocking ultrasonic cookies

    Scientists from the University of Applied Sciences. St. Pölten in Austria developed a mobile application that can detect acoustic cookies and block device tracking using them. The system is called SoniControl.

    Under the cut - tell you how the application works.


    / Flickr / Pete Sheffield / CC

    Why did you need the application


    In 2015, SilverPush introduced ultrasonic cross-device tracking. It allowed billboards or banners in public places (in shopping centers, stadiums, etc.) to produce high-frequency sounds that were picked up by mobile device microphones. Receiving a signal from the lighthouse, the smartphone showed the owner an advertisement for a nearby store or cinema.

    At one time, even the American Center for Democracy and Technology ( CDT ) and the US Federal Trade Commission ( FTC ) were concerned about the problems associated with the new technology . The bottom line is that applications could decipher these signals and determine what the user is currently seeing and what sites he is accessing. Scientists fromBraunschweig Technical University found that the actions of users in this way tracked about two hundred Android applications. As a result, Google even had to remove some of them from the Play Store.

    A group of researchers from University College London ( UCL ) and the University of California at Santa Barbara ( UCSB ) also showed that using ultrasonic beacons users can be deanonymized.

    The developers of the SoniControl project are concerned that this compromises the confidentiality of user data. Therefore, we developed our ultrasonic firewall.

    How does SoniControl work


    SoniControl is implemented in C ++ and Java. During operation, the application creates a model of background ultrasonic noise, and then tracks its changes (that is, it searches for extraneous signals). For this, the signal is converted from a time representation to a frequency representation, which makes it possible to estimate the amplitude of the signal for each frequency. The processing itself includes the following steps :

    1. Audible frequencies are filtered (a high-pass filter with a threshold value of 17 kHz is used for this);
    2. The spectrogram is normalized;
    3. The normalized spectrogram is added to the background buffer, which adds a list of spectrograms.

    As soon as the background buffer is filled (it takes about 10 seconds), the analysis starts with the following algorithm:

    1. “Current Background Model” is calculated — these are the amplitude values ​​for each frequency;
    2. The constructed model is compared with a normalized spectrogram (for this, the Kullback – Leibler distance is used );
    3. If the calculated distance is large, then this frequency is placed in the “median buffer”;
    4. When this buffer is filled, its median is calculated. If the value obtained is 1, then ultrasonic communication was detected. In this case, the application will prompt the user to block the ultrasound signal;
    5. If an ultrasonic signal was detected, then the background model is “cleared” from the last records so that the system does not consider the modified signal as the norm.


    / Flickr / US Department of Agriculture / PD

    How else can you defend yourself


    IT industry experts believe that to fully protect against tracking devices using ultrasound, you need to start developing industry standards. “Once everything is standardized, the OS developers for mobile devices will be able to implement APIs that prevent applications from accessing the microphone unnecessarily,” says Vasilios Mavroudis from UCL.

    While there are no standards, you can use other methods of protection. One of them - to restrict access to the microphone for applications using the patch for Android. It gives users the ability to block the work of individual applications with an ultrasonic spectrum. And for surfing the Internet, you can install the extensionfor Google Chrome browser that performs similar functions.

    You can also use an application similar to SoniControl - UltraSound Detector, but it helps to detect ultrasound interference simply, and not block it.



    Additional blog reading on the VAS Experts website:




    VAS Experts specializes in the introduction of services for managing and analyzing Internet traffic:

    SCAT DPI | IS SORM | BRAS | DLP systems | Our cases | Events | News



    Also popular now: