  Vehicular Ad hoc Networks (VANETs) are becoming a reality where secure
communication is a prerequisite. Public key infrastructure (PKI) can be used to
secure VANETs where an onboard tamper proof device (TPD) stores a number of
encryption keys which are renewed upon visiting a certificate authority (CA).
We previously proposed a dynamic key distribution protocol for PKI-based VANETs
[1] to reduce the role of the TPD. A vehicle dynamically requests a key from
its nearest road side unit. This request is propagated through network
infrastructure to reach a CA cloud and a key is securely returned. A proposed
key revocation mechanism reduced the number of messages needed for revocation
through Certificate Revocation List (CRL) distribution. In this paper,
performance evaluation and security of the proposed dynamic key distribution is
investigated analytically and through network simulation. Furthermore,
extensive analysis is performed to demonstrate how the proposed protocol can
dynamically support efficient and cost-reduced key distribution. Analysis and
performance evaluation results clearly make the case for dynamic key
distribution for PKI-based VANETS.
