Distributed Denial of Service (DDoS) attacks cause devastating effects on the web services and hence harm the digital availability. The DDoS attackers use vulnerabilities exposed through new networking technologies like wireless, mobile, IoT, and associated protocol weaknesses for bringing down the networks and servers.Owing to availability of easily available tools and botnet armies, the DDoS attack incidences in the internet world are increasing day by day. Several techniques have been proposed by the researchers against DDoS attacks. This paper concentrates on the utilization of one of the latest and most promising technologies, that is, blockchain technology against DDoS attacks. The blockchain technology is rapidly finding use in various applications ranging from financial to gaming; this is because of its stable, decentralized, and secure architecture. The DDoS solutions based on blockchain are still in infancy and some solutions provide only architectural details without bothering about the implementation details. This paper presents a study of the blockchain-based DDoS solutions. It also compares the existing blockchain-based techniques against DDoS attacks and analyses them. This paper facilitates the development of future research proposals in this emerging area of blockchain technology. K E Y W O R D S blockchain, communication security, Denial of Service, Distributed Denial of Service, Ethereum blockchain, public blockchain, smart contract 1 Security Privacy. 2020;3:e96.wileyonlinelibrary.com/journal/spy2

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In wireless sensor networks (WSNs), sensor nodes are deployed densely in large numbers to increase the quality of services (QoS). However, QoS is significantly affected by faults in such networks. The probability of faults in WSNs increases with increase of sensor nodes. In order to provide better QoS, it is essential that faulty nodes should be diagnosed and handled timely without affecting the underlying work of the network. In this paper, our main focus is on diagnosing transient and permanent fault by communicating an optimal number of messages. We propose a mechanism to diagnose such faults without degrading the throughput of WSNs. The proposed approach is reactive in nature, which during fault diagnosis generates traffic smoothly in the network due to which the network never degrades its performance. Scheme also allows faults to occur during diagnosis process. The result shows that our scheme diagnoses faults correctly and efficiently and is able to maintain the desired throughput during fault diagnosis.

In recent years, Wireless S ensor Networks (WS Ns) have gained much attention because of its varying applications from catastrophic region to industrial and household region. In few applications, sensors are deployed in extreme environmental conditions. Hence, node access is not possible in that scenario. Therefore, a large number of sensor nodes are deployed in the target field so that node replacement problem is eliminated. Also, coverage is a very important parameter because it measures how effectively a target field is monitored by the sensor network. This paper focuses on the coverage issue in wireless sensor networks. Initially, three different types of coverage issues are discussed. Then, full coverage issue is examined by considering different points such as node type, deployment type, relation of communication range to sensing range, strategy used to detect full coverage and positioning based/independent algorithms. S ome applications of wireless sensor networks are given. Finally, research challenges in the field of area coverage are discussed.