Discovered that smartphones can allow Bluetooth signals to track the user

Discovered that smartphones can allow Bluetooth signals to track the user

A team of engineers at the University of California, San Diego has shown for the first time that the Bluetooth signal emitted by our mobile phones has a unique fingerprint that can be used to monitor and track the movements of individuals.

The idea of ​​using Bluetooth beacons for less “orthodox” purposes has been put forward many times. However, for the first time, researchers have been able to show that it is feasible to track individuals.

Image of device for finding Bluetooth connection

Your smartphone user can "report" where they have gone

Mobile devices, including phones, smart watches and fitness bands, constantly transmit signals, called Bluetooth beacons, At a rate of approximately 500 beacons per minute. It enables features like Apple's Find My Network's "Find My" lost device tracking service; COVID-19 allows tracking applications, and connects the smartphone to other devices, such as wireless headphones.

Previous investigations have already made it possible to identify the existence of wireless fingerprints in WiFi networks and other wireless technologies. The UC San Diego team had a strong belief that this observation could be done very accurately, even using Bluetooth.

This is important because Bluetooth is a more significant threat in today's world as it is a frequent and continuous wireless signal emitted by all our personal mobile devices.

Nishant Bhaskar, a Masters student in Computer Science and Engineering at UC San Diego and one of the leading authors of the paper explained.

A team of researchers from the Department of Computer Science and Engineering and Electrical and Computer Engineering presented their findings at the IEEE Security and Privacy Conference on 24 May 2022 in Auckland, California.

Imperfections that provide unique Bluetooth identification

All wireless devices have minor hardware manufacturing imperfections that are unique to each device. These fingerprints are accidental by-products of the manufacturing process. These imperfections in the Bluetooth hardware lead to unique distortions, which can be used as fingerprints to track a particular device.

For Bluetooth, this will allow the attacker to avoid anti-monitoring techniques, such as constantly changing the address of the device using the mobile network to connect to the Internet.

Tracking personal devices via Bluetooth is not easy. Previous fingerprinting techniques designed for WiFi depend on this fact The WiFi signal consists of a long known sequence called a preamble. But the preambles for the Bluetooth beacon signal are too short.

Instead, the researchers developed a new method that does not rely on the prologue, but analyzes the entire Bluetooth signal. They developed an algorithm that estimates two different values ​​found in a Bluetooth signal. These values ​​vary depending on the faults in the Bluetooth hardware, giving investigators a unique fingerprint of the device.

Real world experiences

Researchers evaluated their observations or screening methods through a number of real-world experiments. In the first experiment, the group found that Of the 162 mobile devices seen in public places like cafes, 40% were recognizable Uniquely

He then expanded the experience and observed 647 mobile devices on public roads for two days. The team found that 47% of them had unique fingerprints on their devices. Finally, researchers used fingerprints and followed a study volunteer-owned mobile device to perform a direct observation attack when they enter and leave their home.

Bluetooth: Is this discovery worrisome?

While this finding is worrisome, the researchers also uncovered a number of challenges that the attacker faces in practice. Changes in ambient temperatureBluetooth, for example, may change fingerprints. Some equipment also sends Bluetooth signal with different strengthsAnd this affects how far these devices can be tracked.

Experts also note that the attacker must have a high level of experience for their method, so there is no possibility of a widespread threat to people today.

Despite the challenges, the group found that Bluetooth tracking is feasible for a large number of devices. It also does not require sophisticated equipment: The attack can be carried out with equipment costing less than 200 euros.

IPhone control center image

When you enable or disable Wi-Fi or Bluetooth using the corresponding buttons in the Control Center, the device instantly disconnects from Wi-Fi and Bluetooth accessories. However, Wi-Fi and Bluetooth will be available so that you can unlock with AirDrop, AirPlay, Apple Pencil, Apple Watch, Continuity Features like Handoff and Instant Hotspot, Instant Hotspot, Location Services and Apple Watch.

So how can the problem be solved?

Basically, the Bluetooth hardware needs to be redesigned and replaced. But researchers believe that other, simpler solutions can be found. The team is currently working on ways to hide Bluetooth fingerprints through digital signal processing in Bluetooth device firmware.

Those responsible for this study are also exploring whether the method they developed could be applied to other types of devices. Moreover, they realized this Just turning off Bluetooth may not be necessary That all phones release Bluetooth beacons. For example, beacons are still emitted when turning off Bluetooth in the Control Center on the home screen of some Apple devices.

To our knowledge, the only thing that definitely prevents Bluetooth beacons is turning off your phone.

Bhaskar said.

Despite all of this revealing, investigators are wary of saying that they can track personal devices Can't get any information about device owners.

The study was reviewed by the Campus Internal Review Board and the Campus Council.

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