Security in this world of digital computing plays a typical role, since all the operations are automated and large volumes of data are being maintained in the servers. Cloud computing is one of the evolving technologies where a huge volume of storage is made on-line, data and services are also distributed. Because of its distributed nature, they have become easy targets for the intruders to exploit the information. The well known Distributed Denial of Service (DDoS) attack is the most prominent attacks in this area of computing. DDoS is the single largest threat to internet and internet of things. This paper provides a wide survey on various DDoS attacks, their vulnerabilities and countermeasures proposed against them. Also this paper provides an in-depth analysis on effects of DDoS attacks in the Cloud environment. Through the analysis done it will be useful for designing a secured cloud infrastructure which will abide the DDoS attacks.

In a Blockchain network multiple nodes across the network verify each transaction and preserve them without having a centralized authority. Verification and insertion of transactions are achieved through distributed cryptographic mechanism called consensus protocol. Consensus protocol involves the application of reputable concepts like Distributed Computing (P2P Networks), Cryptography and consensus algorithms. Traditional motivation for application of Consensus Protocols is to warrant reliability in the distributed systems. The basic assumption behind this protocol is, a `value' must have been proposed by some truthful node in the distributed system. Distributed consensus is attained once all the nodes present in the system agrees and approves the same value. At any given time, all nodes have a sequence of block of transactions, they have already reached consensus on. Also each node has a set of outstanding transactions it has heard about from other nodes. This consensus is achieved via various algorithms which serve as the backbone for Blockchain architecture. Once the transactions are verified, they will be included in the existing chain. The main advantage of such systems is the fact that they are immutable, transparent and distributed. Though stated simple, reaching consensus may be difficult due to various reasons such as crash of active node, presence of malicious nodes, faults in the network, latency (no global time) and not all pairs may be connected. A consensus algorithm ensures that the one and only version of truth gets added into the network, in addition to keeping malevolent people from tampering the network. It also makes sure that the system is fully decentralized. If everyone in the network is strictly honest, there is no need of consensus, however the probability of such existence is very less. Hence, we are undeniably in need of virtuous consensus algorithms for a strong, immortal Blockchain network. The process of selection and enactment of the suitable and right consensus protocol is the key for efficacious Blockchain network. This paper describes about distributed consensus and various algorithms which may be applied for implementation of a Blockchain network.

Internet of Things (IoT) is the predominant emerging technology that targets on facilitating interconnection of internet-enabled resources. IoT applications concentrate on automating different tasks that facilitate physical objects to act autonomously without any human interventions. The emerging and current IoT applications are determined to be highly significant for improving the degree of efficiency, comfort and automation for its users. Any kind of security breach on the system will directly influences the life of the humans In this paper, a comprehensive review on Privacy requirements and application layer Security in Internet of Things (IoT) is presented for exploring the possible security issues in IoT that could be launched over the individual layers of IoT architecture. This review explores different challenges of classical security solutions that are related to authentication, key management and cryptographic solutions.It also presents the details of existing access control and device authentication schemes with their pros and cons.

Security has emerged as the most concerned aspect of cloud computing environment and a prime challenge for the cloud users. The stored data can be retrieved by the user whenever and wherever required. But there is no guarantee that the data stored in the cloud server has not been accessed by any unauthorized user. The current cloud framework does not allow encrypted data to be stored due to the space and storage cost. Storing secret data in an unencrypted form is vulnerable to external attacks by both illegitimate customers and a Cloud Service Provider (CSP). Traditional encryption techniques require more computation and storage space. Hence, protecting cloud data with minimal computations is the prime task. Secured Document Sharing Using Visual Cryptography (SDSUVC) technique proposes an efficient storage scheme in a cloud for storing and retrieving a document file without any mathematical computations and also ensures data confidentiality and integrity.

Internet of things (IoT) creates communication between the sensor nodes and smart devices through the internet to collect the data. The utilisation of IoT in the medical field brings more advantage to the patients and doctors for effective monitoring. The confidentiality of the medical data is a crucial factor need to be taken care of by the medical- IoT (M-IoT). This paper concentrates on developing a secure mechanism for medical data management. In this paper, we develop an architecture for managing the large volumes of medical data generated by the sensor nodes. This architecture will provide secure communication for data sharing among doctors and patients in normal and emergency conditions. As a next step, we propose the security mechanism for improving the data integrity and confidentiality. The proposed mechanism uses symmetric encryption and attribute-based encryption to achieve the performance. The simulation results prove the efficiency of the proposed system.