A Study on Distributed Consensus Protocols and Algorithms: The Backbone of Blockchain Networks

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.