## 4 Authorization and Access Control in the Smart Grid (SG) Network
Their approach is based on the additive homomorphic encryption scheme and the attribute-based encryption that overcomes the drawbacks existing in a scheme by [PERSON] _et al._[89]. [PERSON] _et al._[93] recommended a fault tolerant fine-grained access control scheme, which involves fuzzy identity-based encryption with lattice-based access control and detect error-correction coding. This scheme resists against the corruptions implied by the noisy channels and the environmental interferences. Recently, [PERSON] _et al._[88] introduced a dynamic access model for secure user services in the SG, which is based on the appropriate access context type for the SG users. The approach applies a context-based user security policy to enable users' dynamic access control. There are many other authorization schemes for the SG based on a service oriented architecture (SOA), reference architecture, modeling for interconnected domains, RBAC modeling, multi-authority access control for attribute revocation, and multilevel multi-factor authentication and attribute-based authorization. The SOA based on web services is proposed by [PERSON] _et al._[94] as a convenient way to provide data infrastructure capabilities on the exchanged information such as customer energy feedback, billing and invoicing of variable tariffs, demand side management, and efficient charging of EVs in the SG. However, system overheads are not discussed. Further, [PERSON] _et al._[95] proposed authorization as a service architecture in the SG and [PERSON] and [PERSON] [96] proposed a data-centric access control for the SG services. Various challenges in defining and enforcing consistent authorization policy are described by [PERSON] [97], but the paper does not describe the implementation part and other important aspects, such as overheads and execution time. Further, a new model that extends the network access control from a single security domain to multiple domains for interconnected microgrids, is presented by [PERSON] _et al._[98]. However, it is not clear whether for a large SG network this policy would be effective. A RBAC model-based access control mechanism is extended for the SG systems by [PERSON] _et al._[99] considering the regional division and a concept of areas of responsibility (AOR) for providing an efficient and consistent policy with a greater level of granularity. However, the RBAC based model may significantly increase complexity. Further, a multi-authority access control with efficient attribute revocation (MAAC-AR) scheme for the SG by [PERSON] _et al._[100] achieves fine-grained access control, collusion resistance, privacy preservation, and secure attribute revocation. Yet, this scheme generates a large storage overhead. Further, a lightweight and efficient security solution for substation automation system is proposed by [PERSON] _et al._[101] to provide multilevel multi-factor authentication and attribute-based authorization by deploying public key certificates, and zero-knowledge protocol-based server-aided verification. As we discussed in this section, authorization is important for supporting secure communication among various entities of the SG. National Institute of Standards and Technology (NIST) also suggested a distinct need for a lightweight, secure, and efficient AA protocol to mitigate intrusion and distributed DoS (DDoS) attacks targeting resource-intense AA mechanisms [7]. In the view of large network systems, such as smart grid, a decentralized access control scheme is recommended in order to reduce the overall cost of adding and deleting entities in the system. Furthermore, ABAC is preferred over the user-based and the RBAC when the system is defined with large attributes or the user role is computed dynamically. Although some researchers presented attribute-based decentralized access control scheme, such as [92] and [88], they either do not justify resistance against security attacks or generate large overhead.