# Secure PBFT Consensus-Based Lightweight Blockchain for Healthcare Application
## 1 Introduction  
The present Internet of Things (IoT) has gained the interest of every individual who seeks to accomplish their daily activities, or needs them completed in an accurate and faster manner, through IoT-based applications. In the healthcare domain, the IoT devices have a significant role in accessing real-time health parameters from patients through various body sensors or IoT equipment. The sensed data will be transferred to third-party cloud servers or the central servers later for further processing and analysis. Additionally, the centralized cloud architecture is more prone to security threats such as DDoS and DoS. Despite that, the collected data should be secured from intruders by implementing modern security policies and privacy reserving techniques at distinct levels of the IoT architecture [1]. Even though blockchain technology was invented as a cryptocurrency by [PERSON] in the year 2009, the recent innovations and research have proven promising results in securing data by storing the data as transactions in distributed ledgers. The individual blocks of the blockchain are cryptographically linked together to form a chain of blocks. Moreover, each transaction in the block is verified by a group of miners before adding it to the blockchain. Modern cryptographic techniques such as asymmetric cryptography, digital signatures, and hash functions are incorporated to make the blockchain tamper-proof [2]. Apart from tamper resistance, the blockchain adopts decentralized architecture, anonymity, and enhanced security; furthermore, because of these properties the blockchain is widely being adopted in healthcare [3], supply chain management [4], the industrial IoT [5], and smart city domains. Figure 1 shows the various use cases of blockchain in the healthcare domain. Ever since the invention of the blockchain, many researchers and organizations have contributed to the evolution of the ledger technology, resulting in three differentstages, from Blockchain 1.0 through 3.0. Blockchain 1.0 is the initial and simplest version of a distributed ledger, Blockchain 2.0 is the second generation distributed ledger, where the concept of Smart Contracts was introduced along with enhanced capabilities of Blockchain protocols. Blockchain 3.0 is the advanced version of distributed ledger technology with improved sustainability, scalability, cost-effectiveness, more decentralization, and security. A fusion of traditional IoT healthcare systems with decentralized blockchain technology will be a significant solution to overcome the security, privacy, and reliability concerns of the IoT, ensuring integrity and authenticity of medical data. IoBHealth--an IoT-enabled blockchain framework [6], provides a trusted, secure, transparent, and efficient environment for accessing and managing electronic health records. Most of the IoT devices in the networks are battery-operated [7], with minimal computational capability, minimal resources, and minimal storage capacity. Because of these properties of IoT devices, the integration of the IoT and blockchain is a challenging task. Furthermore, the IoT devices cannot sustain the existing cryptographic techniques and consensus algorithms of the blockchain. Many researchers have proposed various modified versions of the blockchain, such as the lightweight blockchain [8] for resource-constrained IoT devices with an optimized consensus algorithm [9], lightweight cryptographic techniques, and optimized storage techniques without compromising the security and privacy of the devices [10]. Even though the lightweight cryptography techniques are designed to target the resource-constrained IoT devices to work with minimal energy and resources in a faster manner, the major concern of lightweight cryptography is minimal security [11]. Additionally, the initial mathematical computations make it more complex, hence the implementation will be difficult.