# A Novel Security Architecture for WSN-Based Applications in Smart Grid
## 2 Security in WSN-Based SG
### Related Work  
The security solutions for WSN-based application in the SG has been extensively studied recently. The authors in [2] proposed a framework to detect DoS attacks and prevent the direction of the attack to the sink node. The proposed framework blocks suspicious nodes that may cause a DoS attack. If the difference between the current node's request time and its last request time is less than a predefined threshold the node is blocked. Furthermore, the access information of the blocked node is stored, and with each request it sends, the number of requests is incremented. Hence, the suspicious nodes are detected through the number of requests. The limitation in this work is the fact that it is unreasonable to block the node because it may send two or three requests in less time than the predefined threshold. The authors in [12] proposed an adaptive and channel-aware forwarding attack-detection system to detect selective forwarding attacks in WSNs. The authors proposed to divide the network lifetime into a series of evaluation periods and estimate the normal packet loss ratio for every evaluation period to assess the forwarding behavior. In the first phase, the normal packet loss ratio is estimated for all sensor nodes, where the loss of a packet is affected by radio link quality. In the second phase, the sensor nodes monitor their neighbors to evaluate a reputation score periodically. In the third phase, each sensor node computes the probability of attack for its neighbors then it broadcasts the score. The limitation in this work is the use of a non-encryption-based technique which does not satisfy the required security services in the context of WSNs and SG. [PERSON] et al. [7] proposed a scheme based on the hybrid cryptography approach employing public-key cryptography to provide confidentiality and integrity in the transmission of data between sensor nodes. In their scheme, a central CA signs the public key and the network address of each sensor node and redistributes the key, address, and signature. The keys exchange is initiated during a handshake based on certificates. The result of this handshake is two keys generated to be used in symmetric encryption. The limitation of this work is that the central CA represents a single point of failure. [PERSON] and [PERSON] [8] proposed to implement a PKI for the SG using wireless communication networks. In the registration process, the binding of the users' entity with a public key is established using the digital signature. A RA ensures the rightness of the binding after the registration process and the CA issues the certificate to the users. Secure communication with a resource starts with a certificate-signing request (CSR) sent to the RA. The validation authority gives the status of the certificate to a relying party (RP) to access secure resources. In this approach, the centralized CA also represents a single point of failure. The authors in [9] proposed a hierarchical PKI for SG. The proposed PKI consists of five levels. The first level named the master level is the base of trust in the system. Its role is to issue the certificate to the next level, its public key is known by all devices, also all devices can communicate with it. Levels two, three, and four have less validity than the first level. Each level issues a certificate to the next level. As we descend in the hierarchy, the responsibility of level narrows to a smaller area. The last level has no validity to issue the certificates, it can just communicate with other devices. The shortcoming of this work is the fact that the master level is considered the base of trust in the system which makes it a single point of failure. The authors in [10] aim to improve an existing PKI in a SG environment. They propose to divide the SG into groups based on the hierarchical communication network to distribute the trust authority (TA) among the groups to deal with the single point of failure problem. In a WSN deployed in a Smart Grid.