# Microgrid Cyber-Security: Review and Challenges toward Resilience
## 3 Definitions and Overview  
### Cyber-Physical Security  
The IEA (International Energy Agency) defines energy security as \"the uninterrupted availability of energy sources at an affordable price\". Traditionally, security used to be achieved on two fundamental levels; short-term security that deals with the stability of the demand-supply procurers, and the dynamism that enables the energy system to adapt as quickly as possible to sudden changes in the grid loads. Moreover, long-term security focuses on investments that support economic and sustainable development requirements. Recently, with the arrival of smart grids which are essentially defined according to IEEE 2030-2011 standard, as a composition of three interoperability infrastructures, as set forth in Figure 1. This suggested interdependency has led the security problem to grow in complex imposing supplementary challenges threatening of introducing easier ways of causing damage to the fundamental security concerns, all along with creating new ones. Figure 1: Smart grid architecture in compliance with IEEE 2030. Consequently, recent security assessment has focused on identifying the potential vulnerabilities introduced by the cyber layer and analyzes the possible impacts on energy systems, which has given birth to a brand new research area called cyber-physical security. A cyber-physical system is co-engineered collaborating domains of physical and computational counterparts, in which the crucial system tasks are basically handled with its physical part, while informatically enhanced processes-normally referred to as cyber- are responsible for maximizing the exploration of intelligent devices and application [13]. The reason why academia recently chosen to add the term \"physical\" to the equation is to shed light over the emerging threats imposed by connecting these two fundamentally different infrastructures together, which practically may lead to problems that do not particularly belong to a failure of either systems [14]. In light of these assumptions, further investigation is still needed to either confirm or deny the putative relationships [15]. The most indispensable objectives of security requirements considerations of any data transferring communication in the IT network security are known as CIA-triad, which stands for Confidentiality, Integrity, and Availability, respectively. According to The National Institute of Standards and Technology (NIST)'s guide on cybersecurity strategy, architecture, and high-level requirements, Confidentiality refers to \"Preserving authorized restrictions on information access and disclosure, including means for protecting personal privacy and proprietary information... \" [44, U.S.C., Sec. 3542], and a loss of confidentiality results in unauthorized disclosure of information. Whereas Integrity is \"Guarding against improper information modification or destruction, and includes ensuring information non-repudiation and authenticity... \" [44, U.S.C., Sec. 3542] in other words, integrity is the unauthorized modification or destruction of transferred information. Availability, on the other hand, means \"Ensuring timely and reliable access to and use of information... \" [44, U.S.C., Sec. 3542] as if altering availability will lead to the disruption of the access to or use of information or an information system. Smart grid security is also built upon the previous trestles, but with a difference in priority order, where availability comes on top of the requirements, followed by integrity, accountability, and finally confidentiality. Other referencing emphasizes the accountability as additional security criteria [16]. This sequence of importance goes back to the severity of impacts resulting from tampering with these criteria. Attackers can penetrate the smart grid communication systems using vulnerable entry points in the logical border surrounding a network, known as the Electronic Security Perimeter (ESP).