Woman approaching a car, symbolized localization using BLE and UWB satellites.

Phone as a Key – How does the Huf digital car key work?

Tech & Trends |

Car access via smartphone: Phone as a Key, the digital car key by Huf, combines three advanced technologies for data transmission to provide a comfortable and secure hands-free car access experience. The combination of Ultra Wideband (UWB) and Bluetooth Low Energy (BLE) provides high-precision localization that makes relay station attacks impossible. Moreover, the AUTOSAR-compliant system by Huf enables high energy efficiency.

Text: Manuel Dohr

For the digital car key Phone as a Key, Huf uses three signal transmission methods that are available in modern smartphones: Bluetooth Low Energy (BLE), Ultra Wideband (UWB) and Near Field Communication (NFC). All three have their respective strengths for secure and comfortable car access. UWB and BLE enable precise localization of the vehicle user when approaching the car and perfectly complement each other. Find out exactly how the technologies work and what advantages they offer in the digital car key Phone as a Key by Huf right here.

Gentle wake-up with BLE - what is Bluetooth Low Energy?

The automotive experience starts when you approach the vehicle. And BLE wireless technology plays a crucial role in this experience, which vehicle owners and automobile manufacturers alike increasingly demand as a comfortable hands-free car access solution.

Bluetooth Low Energy is a modified version of  Bluetooth, which is used, for example, to stream media from a smartphone to an audio device. This data transmission system, also called Classic Bluetooth, requires a relatively high amount of energy. As a result, the battery of a smartphone can be drained quite quickly when Classic Bluetooth is activated.

BLE, on the other hand, needs such little energy that built-in Bluetooth low-energy chips with small batteries can operate over an extended period of several years. This is crucial for a continuously reliable communication between many devices on the Internet of Things.

Today, BLE is included in all popular mobile devices. BLE's low-energy mode is ideal for use in car access systems such as Phone as a Key. One of the advantages: The system only needs very small amounts of data to ensure reliable and secure communication between smartphone and vehicle. For pairing BLE-enabled devices, Phone as a Key by Huf uses only algorithms that comply with the BLE SIG standard. This standard, developed by the Bluetooth Special Interest Group (SIG), ensures a high level of security. The SIG is an international interest group of numerous well-known companies dedicated to the further development and distribution of Bluetooth technology.

How does BLE work in detecting a digital car key?

The BLE satellites inside the vehicle will detect when the smartphone with a matching digital car key approaches from a distance of about 30 meters. At this point already, the first data exchange and check of the smartphone car key take place. During this step, the first connection is made between the car and the authorized smartphone of the car user. This keeps energy consumption at the vehicle low.

However, BLE is not precise enough for key localization down to a few centimeters. The insurance-relevant classification in important markets requires that an engine start may only be authorized if the mobile device is clearly located in the interior of the vehicle. This is where UWB comes into play.

High localization accuracy with UWB - what is Ultra Wideband?

Typically, radio technologies utilize continuous signals. UWB, on the other hand, only sends short pulses. To put it metaphorically, conventional radio transmissions can be thought of as long flute melodies, whereas UWB is like short drumbeats that produce a fast echo. These UWB pulses span a very wide frequency range - hence the name "ultra wideband".

UWB achieves a high localization accuracy for real-time localization systems. Using pulses of short duration, it can detect the position of an object in a room with an accuracy of just a few centimeters. At the same time, UWB can be used with other radio technologies such as WLAN and Bluetooth in the same environment.

Woman approaching a car, symbolized localization using BLE and UWB satellites.

Blue radius: The vehicle detects the approaching digital key via BLE (Bluetooth Low Energy). Red radius: High-precision localization and secure authentication at short distance is performed via Ultra Wideband (UWB).

How is the smartphone position localized via UWB with the digital car key?

To achieve a precise localization, Phone as a Key by Huf uses UWB from a distance of about ten meters between the smartphone and the vehicle to position the mobile device carrying the digital car key. This is realized using in-car transmitting/receiving units known as satellites. Ideally, four of them are located in the "corners" of the vehicle, as this enables them to localize the mobile device very precisely under almost all conditions.

Two additional UWB satellites are installed in the passenger compartment. Thus, Phone as a Key provides highly accurate localization and meets all critical requirements. The rearmost of the two UWB satellites in the interior can be integrated into the roof lining and can thus also be used to monitor the rear seats and the trunk. This opens up possibilities for additional functions, especially for advanced safety systems such as Child Presence Detection by Huf.

Animated scene: Woman moving towards a parked vehicle, holding a handbag with her smartphone in it. In the foreground: car hood with Huf logo. Woman using smartphone with Phone as a Key app by Huf, car key placed next to the phone. Woman walking from a cafe to her vehicle holding a handbag with her smartphone in it. Animated scene: Woman walking from a cafe to her vehicle holding a handbag with her smartphone in it.

How does UWB protect against hacking and relay station attacks on smartphone car keys?

Phone as a Key meets the highest safety standards. One reason for this: UWB makes it possible to measure the "Time of Flight" (ToF). The individual UWB components - smartphone and satellite - each measure the time it takes for the signal to travel from the transmitter to the receiver. Thus, each component can calculate the distance between the two components based on the time measurement. An attacker who extends the signal from the vehicle to the smartphone would also extend the ToF as a result. This makes relay station attacks - where hackers intercept and relay the signal from a key to the vehicle - virtually impossible.

Moreover, data sent via UWB is obviously encrypted. Even if an attacker managed to intercept a signal, the data in it would be useless without the right code. This is because modern UWB systems, such as Phone as a Key by Huf, use secure protocols to exchange keys between devices. Attackers would not be able to extract or copy the codes they contain.

NFC for car access in case of emergency

Even today it is possible that the smartphone battery runs out. Nevertheless, in this case, car owners must be able to access their vehicle and start the engine. Of course, Huf has also thought of this scenario: Phone as a Key therefore uses NFC technology as a fallback solution for car access. Huf was the first automotive supplier worldwide to introduce this into a vehicle, making it possible for the first time to open the car with a smartphone.

NFC transceivers can be installed in door handles, in the B-pillar, as well as in the interior of a vehicle, for example. By holding the smartphone up to the NFC transceiver, the smartphone's NFC chip - which features an integrated secure element - is supplied with the necessary energy to authenticate the digital car key in the smartphone. This allows the vehicle to be unlocked.

Hand holding smartphone with Phone as a Key by Huf in front of a car door handle. Car access with NFC.

Phone as a Key by Huf enables car access even when the smartphone battery is drained, thanks to NFC. After successful authentication of the digital key, the door can be unlocked and the engine started.

AUTOSAR compatibility ensures compatibility with vehicle architectures

In modern vehicles, many different technologies and software come together that have to work hand in hand, communicate with and complement each other - without, of course, leaving any security gaps open. Automobile manufacturers and automotive suppliers must therefore ensure that their components can be integrated into a wide variety of vehicles worldwide.

This can only be achieved if there is a common technological basis. The goal of the Automotive Open System Architecture development partnership, or AUTOSAR for short, is to develop the necessary standards. This project of car manufacturers and suppliers from numerous related industries was founded in 2003 to address the growing complexity of electronic systems in vehicles. The result of this collaboration is an open, scalable software architecture for electronic control units (ECUs) in vehicles.

Phone as a Key by Huf complies with numerous important standards. And needless to say, the system is also AUTOSAR-compliant. The localization and key management software can thus be easily integrated into corresponding vehicle architectures.

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