In the pages of our website we have repeatedly introduced our readers to the results of the Cyber Security Research Center at Ben-Gurion University, Israel. The specialists have already developed three types of attacks that make it possible to extract data from computers protected by the so-called “air barrier. These attacks used electromagnetic waves emitted by the computer, GSM radio waves and even the heat generated inside the system unit of the attacked computer. And recently the same group, led by Mordechai Guri, found another way to steal information, this time with the sound of the fans that cool the processor and system unit of the computer.
Computers protected by an “air barrier” are stand-alone computers or networks that are not directly connected to the Internet or are not connected to other computers or networks that have an Internet connection. Such computers are considered to be as secure as possible against remote hacking, and are used to store and process sensitive and critical information. In some critical cases, even the built-in speakers and microphones are removed from such computers to prevent theft of information through acoustic waves.
Any computer has at least two fans, one to cool the CPU and one to cool the power supply. Some computers may have fans on the video board and on the back of the system unit chassis. During their operation, these fans emit a sound, the frequency of which depends on their speed, which can be adjusted programmatically. This is used by the Israeli-developed malware program Fansmitter, which encodes the frequency of 1000 revolutions per minute logical 0, and the logical 1 corresponds to a fan speed of 1600 revolutions per minute.
An ordinary smartphone can act as a receiver device, which uses its own microphone to receive acoustic signals and is equipped with a specialized application. The signals received from the microphone go through complex mathematical processing, including Fourier transforms, which allows you to isolate the sound of each individual fan. And this system works quite steadily even when there is soft music playing in the room.
Naturally, this technology allows to steal a very small amount of data, but it is enough to transmit encryption keys, user names, passwords, keystroke history, etc. At a distance of about 4 meters from the attacked computer, the system provides a transmission speed of 15-20 bits per second (just over 1,200 bits per hour), but the researchers are now working to increase that speed several times over.
“We can engage two or more fans of the same computer at once, and in this extensive way we can immediately raise the transmission speed by two or three times,” says Mordecai Guria, “And now we are working on a number of other intensive methods that will allow us to squeeze even more speed from each of the computer’s fans.”