Abstract

Safety application systems in Vehicular Ad-hoc Networks (VANETs) require the dissemination of contextual information about the scale of neighbouring vehicles; therefore, ensuring security and privacy is of utmost importance. Vulnerabilities in the messages and the system’s infrastructure introduce the potential for attacks that lessen safety and weaken passengers’ privacy. The purpose of short-lived anonymous identities, called “pseudo-identities”, is to divide the trip into unlinkable short passages. Researchers have proposed changing pseudo-identities more frequently inside a pre-defined area, called a cryptographic mix-zone (CMIX) to ensure enhanced protection. According to ETSI ITS technical report recommendations, the researchers must consider the low-density scenarios to achieve unlinkability in CMIX. Recently, Christian et al. proposed a Chaff-based CMIX scheme that sends fake messages under the consideration of low-density conditions to enhance vehicles’ privacy and confuse attackers. To accomplish full unlinkability, in this paper, we first show the following security and privacy vulnerabilities in the Christian et al. scheme: Linkability attacks outside the CMIX may occur due to deterministic data sharing during the authentication phase (e.g., duplicate certificates for each communication). Adversaries may inject fake certificates, which breaks Cuckoo Filters’ (CFs) updates authenticity, and the injection may be deniable. CMIX symmetric key leakage outside the coverage may occur. We propose a VPKI-based protocol to mitigate these issues. First, we use a modified version of Wang et al.’s scheme to provide mutual authentication without revealing the real identity. To this end, the messages of a vehicle are signed with a different pseudo-identity “certificate”. Furthermore, the density is increased via the sending of fake messages in low traffic periods to provide unlinkability outside the mix-zone. Second, unlike Christian et al.’s scheme, we use the Adaptive Cuckoo Filter (ACF) instead of CF to overcome the false positives’ effect on the whole filter. Moreover, to prevent any alteration of the ACFs, only RUSs distribute the updates, and they sign the new fingerprints. Third, the mutual authentication prevents any leakage from the mix zones’ symmetric keys by generating a fresh one for each communication through a Diffie–Hellman key exchange.

Highlights

  • Intelligent transportation systems (ITS), Vehicular Ad Hoc Networks (VANETs), are constantly growing in importance

  • The two types of communication performed by VANETs are Vehicle to Vehicle (V2V) and Vehicle to Infrastructure (V2I), which communicate through the latest Radio Access Technology (RAT) IEEE 802.11bd for Dedicated Short Range Communications (DSRC) and New Radio

  • Freudiger et al [13] suggested encrypting the exchanged messages inside the mix-zone and called it the cryptographic mix-zone (CMIX) strategy. This relies on a symmetric key to share safety messages within the mix-zone, which ensures that all vehicles can use the same key to avoid linkability within the mix-zone, whereby the Roadside Units (RSUs) provides the symmetric key to all vehicles within the mix-zone [8]

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Summary

Introduction

Intelligent transportation systems (ITS), Vehicular Ad Hoc Networks (VANETs), are constantly growing in importance. Established safety requirements based on Vehicle Public Key Infrastructure (VPKI) require multiple Certificate Authorities (CAs) to administer certificates for the underlying bodies [6,7]. These CAs permit long-term certificates for vehicles and RSUs after registration. Some techniques recommend that vehicles set up a silent period, i.e., their transmitters stay off (do not send messages) for a specific duration after changing their pseudo-identities, they can still accept and process incoming messages [8] While this tends to make tracking very difficult, safety applications may be impaired because vehicles cannot send safety messages during this time. The VPKI should have the following list of CAs [8,14]: 1. The root CA (RCA) 1 is at the top of the hierarchy, serving as a governance body that certifies other intermediate authorities

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