Traditional vehicle access systems, relying on physical keys or low-precision radio technologies such as RFID (Radio-Frequency Identification) or LF/HF (Low Frequency/High Frequency), are inherently susceptible to relay attacks. In these scenarios, the authentication signal is intercepted, retransmitted, and amplified, falsifying the actual distance and enabling unauthorized access. A fundamental flaw in these systems is the absence of a precise distance measurement mechanism. Ultra-Wideband (UWB) technology, utilizing nanosecond-duration pulses across a wide frequency spectrum, represents a breakthrough in secure access. Its key advantage is sub-centimeter precision in distance and position measurement, making it ideal for mitigating relay attacks through precise physical proximity verification of the authenticating device. This article analyzes the Aliro standard, a core component of the CCC Digital Key specification, in terms of its secure ranging protocols and cryptographic implementations that redefine vehicle access security and convenience.

UWB Technology Fundamentals and its Role in Secure Access

Principles of UWB Operation

UWB transmits data via ultra-short pulses (nanosecond scale) with low spectral power density, spread over a broad frequency spectrum (e.g., 3.1 GHz to 10.6 GHz), compliant with the IEEE 802.15.4z standard. (Source)

The primary distance measurement mechanism is Time of Flight (ToF), which quantifies the propagation time of radio impulses. Practically, Round-Trip Time (RTT) is employed, measuring the time from sending a challenge pulse to receiving its response. Distance d is calculated using the formula:

UWB Digital Keys

Where T_RTT is the measured round-trip time, T_Turnaround is the known processing delay of the responding device, and c is the speed of light in the medium. UWB’s precision, achieving millimeter accuracy, stems from its ability to distinguish the direct signal path (Line of Sight – LoS) from reflected paths (multipath interference) due to its wide bandwidth and short pulses.

UWB System Architecture for Vehicle Access

Key architectural components include:

  • In-Vehicle UWB Modules: UWB transceivers integrated with electronic control units (ECUs), e.g., the BCM (Body Control Module), featuring strategically placed antennas for 3D positioning.
  • Mobile Device/Digital Key UWB Module: Implemented in smartphones, smartwatches, or dedicated digital keys.
  • Secure Element (SE): A hardware cryptographic module, present in both devices, responsible for secure key storage and performing cryptographic operations within a tamper-resistant environment. (Source)

The system functions by exchanging UWB pulses for distance measurement, occurring in parallel with cryptographic authentication before vehicle access is authorized.

The Aliro Standard: Architecture and Secure Ranging Protocols

The Aliro standard, part of the CCC Digital Key specification, aims to establish a unified, interoperable, and highly secure digital key protocol, effectively eliminating relay attack vulnerabilities. (Source)

Multi-Layered Security Approach

Aliro implements layered protection:

  1. Physical/Radio Layer: Utilizes precise UWB ranging as the fundamental distance verification mechanism.
  2. Ranging Protocol Layer: Incorporates cryptographic distance bounding protocols that actively verify the physical proximity of the device. These protocols measure response times to rapid challenge-response exchanges, identifying and rejecting any anomalous delays, e.g., those caused by a relay attack .
  3. Cryptographic Layer: Ensures mutual authentication, confidentiality, and data integrity through advanced cryptographic mechanisms.

Aliro’s Secure Ranging Protocol

Aliro extends beyond basic ToF measurement through:

  • Secure Distance Bounding: Encompasses initialization, rapid bit exchange (with a nonce generated by the verifier), and authentication phases. It is resilient to relay and man-in-the-middle (MITM) attacks via temporal verification and cryptographic binding [10].
  • Ranging Data Filtering and Analysis: The system aggregates redundant ToF measurements from multiple antennas. Advanced filtering algorithms and trilateration (based on distances, not angles) are applied to construct a consistent key position model, enhancing resilience against spoofing and jamming .
  • Signal Manipulation Resistance: Techniques to prevent active signal manipulation are incorporated, including randomization of signal parameters and cryptographic authentication of UWB frames, enabled by the scrambled timestamp sequence (STS) in IEEE 802.15.4z HRP UWB [4].

Table 1: Comparison of Ranging Protocols and Security Levels

UWB Digital Keys

Cryptographic Aspects of the Aliro Standard

Strong cryptography forms the foundation of Aliro’s security, ensuring authentication, integrity, confidentiality, and resistance to replay attacks.

Aliro’s Cryptographic Architecture

  • Key Management: Keys are generated in high-security environments (e.g., HSM – Hardware Security Modules) and securely provisioned to the Secure Element (SE) in both devices. The SE, as a tamper-resistant chip, protects keys from extraction. Mechanisms for remote key revocation are designed for device loss scenarios.
  • Authentication Protocol: Utilizes mutual authentication based on challenge-response protocols. The use of unique nonces, transaction counters, or timestamps prevents replay attacks. Message integrity is verified using HMAC (Hash-based Message Authentication Code) functions.
  • Cryptographic Algorithms:
    • Simetric: AES-GCM (Advanced Encryption Standard in Galois/Counter Mode) with 128/256-bit keys is used to ensure data confidentiality and integrity in UWB communication and other channels.
    • Asymmetric/Digital Signatures: Elliptic Curve Cryptography (ECC), including ECDSA (Elliptic Curve Digital Signature Algorithm) for digital signatures and ECDH (Elliptic Curve Diffie-Hellman) for secure session key exchange, are applied in key management and certificate-based authentication.
  • UWB Communication Encryption: All UWB data frames (both ranging and commands) are encrypted and cryptographically authenticated, preventing eavesdropping, modification, and injection of malicious data.
  • Resistance to Cryptographic Attacks: Aliro’s design includes resistance to brute-force attacks (through the use of long keys), side-channel attacks (through strict requirements for SE implementations), and replay attacks (through unique session values).

Integration with PKI (Public Key Infrastructure)

Aliro is designed for integration with a PKI, enabling the management of X.509 digital certificates. PKI establishes a chain of trust through a hierarchy of Certificate Authorities (CAs), providing scalable and secure management of device and user identities.

Implementation and Use Cases

Implementation Challenges and Hardware Architecture

UWB deployment necessitates precise placement of multiple antennas (up to 12) within the vehicle for accurate 3D positioning and material interference compensation. Secure management of the entire digital key lifecycle, from generation to revocation, is also critical. OTA (Over-The-Air) updates for UWB modules, SEs, and microcontrollers must be kryptograficznie podpisane i weryfikowane, co wymaga mechanizmu secure boot.

Hardware Architecture of a Secure Access Module with UWB and NFC

(The diagram illustrates the internal structure of an electronic module for secure access, integrating key components: a UWB/NFC module with a Secure Element (SE), a central microcontroller with a Secure Enclave, and a user interface. These components typically include a UWB Transceiver (e.g., NXP SR150), an NFC Controller (e.g., NXP PN7642), a Secure Element (e.g., NXP EdgeLock SE051), and a Main MCU (e.g., NXP MCX W71x) .)

UWB Digital Keys

Business Use Cases

Aliro opens new perspectives in the automotive sector:

  • Keyless Entry/Go: Enhanced security due to relay attack resistance and precise ranging.
  • Car Sharing: Secure and convenient remote management of fleet access.
  • Package/Service Delivery: Temporary, authorized vehicle access for service providers.
  • Corporate Fleets: Simplified access management and monitoring of company vehicle usage.

Risk Analysis and Aliro Standard Resilience

Potential Attack Vectors

  • Ranging Attacks: Include Relay Attack (mitigation: Distance Bounding), Man-in-the-Middle (MITM) on the ranging protocol (mitigation: cryptographic session binding, data filtering), and Jamming/Spoofing UWB (mitigation: interference detection, cryptographic signing of UWB frames using STS).
  • Cryptographic Attacks: Encompass key compromise (mitigation: long key lengths, strong algorithms), Side-channel Attacks (mitigation: strict SE implementation requirements, e.g., physical isolation), and Replay Attacks (mitigation: nonces, counters, timestamps).
  • Vehicle System Attacks: Manipulation of vehicle software or physical access. Requires a holistic vehicle security approach, including secure boot and ECU hardening.

Aliro’s Defense Strategies

Aliro’s integrated approach, combining secure UWB ranging with robust cryptography within hardware security elements, minimizes these risks. UWB precision verifies physical proximity, while cryptography ensures data authenticity, integrity, and confidentiality.

The Future of Digital Keys and Aliro’s Role

The Aliro standard marks a milestone in the evolution of vehicle access, positioning itself as a crucial element for future automotive ecosystems. It is expected to evolve, introducing advanced access scenarios (e.g., biometrics with digital key) and precise in-vehicle positioning for personalization.

Aliro can become the foundation for secure, seamless interaction between vehicles and smart homes, urban infrastructure, or mobility services within the broader vision of Connected Vehicles and the IoT. Aliro’s adoption by automotive manufacturers will significantly accelerate the deployment of digital keys, potentially making them more secure than physical keys.

Conclusion

The Aliro standard for UWB-based digital keys represents a significant advancement in secure vehicle access. By combining precise UWB ranging protocols with robust cryptographic mechanisms, implemented within hardware security elements (SEs), Aliro effectively eliminates vulnerability to relay attacks. This not only provides an unprecedented level of security but also offers an intuitive and seamless user experience, forming the foundation for the next generation of automotive access systems.