  Vehicle-to-grid (V2G) networks have emerged as a new technology in modern
electric power transmission networks. It allows bi-directional flow of
communication and electricity between electric vehicles (EVs) and the Smart
Grid (SG), in order to provide more sophisticated energy trading. However, due
to the involvement of a huge amount of trading data and the presence of
untrusted entities in the visiting networks, the underlying V2G infrastructure
suffers from various security and privacy challenges. Although, several
solutions have been proposed in the literature to address these problems,
issues like lack of mutual authentication and anonymity, incapability to
protect against several attack vectors, generation of huge overhead, and
dependency on centralized infrastructures make security and privacy issues even
more challenging. To address the above mentioned problems, in this paper, we
propose a blockchain oriented hierarchical authentication mechanism for
rewarding EVs. The overall process is broadly classified into the following
phases: 1) System Initialization, 2) Registration, 3) Hierarchical Mutual
Authentication, and 4) Consensus; wherein blockchain's distributed ledger has
been employed for transaction execution in distributed V2G environments while
Elliptic curve cryptography (ECC) has been used for hierarchical
authentication. The designed hierarchical authentication mechanism has been
employed to preserve the anonymity of EVs and support mutual authentication
between EVs, charging stations (CSs) and the central aggregator (CAG).
Additionally, it also supports minimal communicational and computational
overheads on resource constrained EVs. Further, formal security verification of
the proposed scheme on widely accepted Automated Validation of Internet
Security Protocols and Applications (AVISPA) tool validates its safeness
against different security attacks.
