IoT Gateways as Blockchain Nodes
A credit-based mechanism has been proposed by Huang et al.  that ensures better efficiency for simultaneous transactions and confirms system security. For ensuring the confidentiality of sensitive data, a mechanism for managing the data authority is defined that controls the sensor data access. The mechanism is designed on structured blockchain based on directed acyclic graphs, which gives better performance and improved throughput compared with chain-structured blockchain like Satoshi-style blockchain. The case study was conducted for a smart factory and the system was implemented on Raspberry Pi 3 Model B. The architecture design of a smart factory consists of four major components, namely tangle network, wireless sensors, managers, and gateways. The designed architecture is impenetrable to various attacks such as DoS, distributed denial-of-service (DDoS), and Sybil. Sybil attacks generally occur in a peer-to-peer network where the attacker creates multiple active identities to hugely influence the network. To guarantee the optimal trade-off between system security and transactional efficiency, a proof-of-work mechanism has been designed, which ensures that the honest nodes always devour a limited number of resources while enforcing the malicious nodes with increased attack cost. To ensure confidentiality, the authors designed a mechanism for data authority management in which the nodes that collect sensitive data are given the secret key by managers, and with the help of this key, sensor data is encrypted before being posted on the blockchain.
Biswas et al.  have used a network of local peers which narrows the gap between blockchain peers and IoT devices. Without affecting the transactional validation policy followed by peers at both the local and global level, the number of transactions entering the global blockchain is restricted using a local ledger.
The authors proposed a framework based on blockchain technology for IoT which considers both the inter and intra transactions for the corresponding organization. Each IoT device is registered by the certification authority and associated with one of the organizations. Instead of using peers belonging to a global blockchain, a local peer was structured to achieve the interaction with peers belonging to global block- chain network. The designed framework aims to handle the indirect rise in transactions per second for the global blockchain network and increase in ledger storage requirements at peer level. The size of ledger is limited under this framework and is distributed between local and global peers. The transactions between two organizations are validated via a global blockchain network that provides 100% peer validation. In this work, they clearly demonstrated that if the issue of scalability is not addressed, blockchain and IoT cannot be integrated, and that creating a network of local peers allowed the blockchain ledger to spread across all the peers and hence improved scalability.
Badr et al.  designed a novel protocol named pseudonym based on encryption for providing privacy to patients’ data available in the e-healthcare system. The encryption mechanism is blockchain-based in which high-end different authority encryption techniques are used for securing the patients’ confidential data. The public blockchain tier between the healthcare cloud providers and the blockchain tier handling the sensors on patients’ bodies along with the patients’ system on the platform are considered in this approach. The work elevates the anonymity factor in patients’ data by considering blockchain as the anonymity enhancement technology using the multitier architectural model which prevents the system from various attacks such as block enquiry infringement. The solution was evaluated using the MIRACL library, which keeps track of the processing time for all the functions executing within the communication channel. The architecture contains three tiers, where the first tier shows how all the sensor devices are connected to the patient through a gateway or aggregator. The second tier analyses the distribution of the ledger and handles communication within the health record members and provider. In tier three, compliance with the cloud providers is considered and analysed. This framework can handle some of the security vulnerabilities but not all. Therefore, in the future, this model should be modified to handle larger clusters of security issues.