  Blockchain-based Vehicular Ad-hoc Network (VANET) is widely considered as
secure communication architecture for a connected transportation system. With
the advent of quantum computing, there are concerns regarding the vulnerability
of this architecture against cyber-attacks. In this study, a potential threat
is investigated in a blockchain-based VANET, and a corresponding quantum
cyber-attack is developed. Specifically, a quantum impersonation attack using
Quantum-Shor algorithm is developed to break the Rivest-Shamir-Adleman (RSA)
encrypted digital signatures of VANET and thus create a threat for the
trust-based blockchain scheme of VANET. A blockchain-based VANET,
vehicle-to-everything (V2X) communication, and vehicular mobility are simulated
using OMNET++, the extended INET library, and vehicles-in-network simulation
(VEINS) along with simulation of urban mobility (SUMO), respectively. A small
key RSA based message encryption is implemented using IBM Qiskit, which is an
open-source quantum software development kit. The findings reveal that the
quantum cyber-attack, example, impersonation attack is able to successfully
break the trust chain of a blockchain-based VANET. This highlights the need for
a quantum secured blockchain.
