  Vehicular Public Key Infrastructure (VPKI) plays a vital role in ensuring
secure and privacy-preserving communication in vehicular ad hoc networks
(VANETs). However, current VPKI architectures face significant challenges in
terms of scalability, resilience, and privacy preservation. This paper proposes
a novel threshold-based VPKI architecture to overcome these limitations.
Leveraging a Schnorr threshold signature scheme based on elliptic curve
cryptography, the proposed architecture eliminates the reliance on individual
certificate authorities (CAs) and distributes trust among multiple CAs in a
threshold certificate signing approach. This enhances resilience and mitigates
the single point-of-failure vulnerability. The architecture also addresses
sybil-based misbehaviors through a time-restrictive pseudonym design that
eliminates multiple simultaneous use of pseudonyms. Furthermore, the scheme
reduces the size and latency of Certificate Revocation List (CRL) distribution
by clustering multiple CAs in a threshold setting and adopting a
region-specific CRL. The paper presents detailed analysis of the security,
privacy and performance benefits of the proposed architecture. Results from the
performance evaluation shows the improved resiliency, reduced handover rates,
and better scalability potential of the proposed threshold-based VPKI
architecture compared to existing techniques. The proposed threshold-based VPKI
holds great promise in ensuring secure and privacy-preserving communication in
VANETs, paving the way for safer and more efficient vehicular networks.
