## 2 Authentication in the Smart Grid (SG) Network
### Authentication Protocols
#### 2.2.3 Obj-4: Resistance to Attacks and Failures  
Due to having IP-based communication networks, (e.g., Internet), the SG networks are likely to be challenged by a variety of malicious attacks, such as replay, MITM, traffic analysis, impersonation, and DoS. There are certain situations in the SG where the multicast message must be authenticated and its integrity is protected so that the involved entity can know that the received message has come from a legitimate source and has not been tampered over the network. This can happen when phasor measurement units (PMUs) measure voltage and current in a WAN and multicast these parameters to the CCs [49]. Another situation may arise when utility centers multicast demand-response commands to different home appliances and request them to turn-off power during the maintenance or during peak hours of power consumption [50]. In the absence of authentication, an attacker can easily tamper with the message, replay the previous message, or send a fake message to the device that results in an inconsistent state of the SG. In this paper, we consider four broad categories of cyber-attacks in the smart grid communication: interrupting availability, violating integrity, compromising confidentiality, and compromising privacy [51, 32]. Attacks interrupting availability include DoS attack, replay attack, and delay, block or corrupt the communication in the SG. Attacks violating integrity include modification of data exchanged by malicious user and false data injection attack in the SG. Attacks compromising confidentiality in the SG include unauthorized information from network resources, MITM attack, impersonation attack, and attacks on aggregation. Attacks compromising privacy in the SG include user tracing attack, identity theft attack, and attacks on billing systems. Various researchers have proposed solutions to resist the SG system against different attacks. We discuss some recent solutions in this paper. [PERSON] and [PERSON] [52] proposed a scheme that provides mutual authentication between the SM and the data concentration unit (DCU). They claimed that the scheme provides confidentiality and integrity to the transmitted messages and disallows impersonation and MITM attacks between SM and DCU. However, their scheme neither discusses the generated overhead nor provides a complete authentication in HAN. Further, in order to prevent these attacks, [PERSON] _et al._[37, 53] presented a light-weight authentication scheme, which is based on the Diffie-Hellman key exchange protocol and a hash-based MAC. This scheme provides the mutual authentication between only the HAN-GW and the BAN-GW. [PERSON] and [PERSON] [54] proposed a two-factor cyber-physical device authentication protocol in order to prevent cyber-physical attacks in the SG. Their protocol is a combination of contextual factors based on physical connectivity and the conventional authentication factor in the challenge-response protocol. Their solution provides assurance on digital identity of a device as well as its controllability in the physical domain. Recently, [PERSON] _et al._[55] proposed an authentication scheme for the SG system that protects against replay, injection and message modification attacks, by using a Merkle hash tree technique for secure SG communication. However, only a scenario between the HAN and the NAN is considered. Three different authentication mechanisms for the devices in the HAN between gateway--smart meter, smart appliances--HAN, and transient devices--HAN are proposed by [PERSON] and [PERSON] [56]. However, security and overheads of these approaches are not discussed. A robust and efficient protocol based on the elliptic curve cryptography is proposed by [PERSON] _et al._ in [57], to achieve mutual authentication and key agreement between the substation and the smart appliances.