Scientists at the University of California, San Diego have proved for the first time that the Bluetooth signals continuously sent by smart phones have unique "fingerprints" that can be used to track the tracks of mobile phones and users. The research team presented the research results at the Institute of electrical and Electronics Engineers (IEEE) security and privacy conference recently held in Auckland. Mobile devices such as mobile phones and smart watches continuously transmit Bluetooth beacons at the speed of 500 beacons / min. These beacons are used by Apple's find my lost device tracking service and novel coronavirus tracking program. Previous studies have shown that wireless "fingerprints" exist in WiFi and other wireless technologies. The latest research shows that Bluetooth also has such wireless "fingerprints". The researchers explained that the hardware of all wireless devices has some small manufacturing defects, which is equivalent to a kind of "fingerprint", which is an accidental by-product of the manufacturing process. These flaws in Bluetooth hardware can lead to unique distortions that can be used as "fingerprints" to track specific devices. However, tracking a single device via a Bluetooth signal is not easy. The reason is that the leading sequence of WiFi signal is very long, while the leading sequence of Bluetooth beacon is very short. Therefore, the "fingerprint" technology previously built for WiFi is useless for Bluetooth tracking. To this end, researchers do not rely on the preamble sequence, but view the entire Bluetooth signal, and develop an algorithm that can estimate two different values in the Bluetooth signal. These values change according to the defects in the Bluetooth hardware, providing researchers with the unique "fingerprint" of the device. The researchers evaluated their tracking methods experimentally. In the first experiment, 40% of the 162 mobile devices seen in public places (such as coffee shops) were uniquely identifiable. Then they expanded the scale of the experiment, observed 647 mobile devices in two days, and found that 47% of the devices had unique "fingerprints". Researchers pointed out that attackers face several challenges if they want to attack devices: changes in ambient temperature may change the "fingerprint" of Bluetooth; Some devices will send Bluetooth signals with different power, which will affect the distance that these devices can be tracked. Moreover, the new approach requires a high level of expertise on the part of the attacker and is therefore unlikely to pose a widespread threat to the public. However, they also warned that Bluetooth tracking may be applicable to a large number of devices and can be attacked with devices less than $200. To solve this problem, the Bluetooth hardware must be redesigned and replaced. However, they are currently studying simpler solutions, such as hiding the Bluetooth "fingerprint" by processing the digital signals in the firmware of Bluetooth devices. (Xinhua News Agency)