Contextualizing Consensus Protocols in Blockchain: A Short Survey

Consensus protocols are mechanisms that enable a group of entities to reach an agreement on a specific subject. In blockchain systems, consensus protocols are the cornerstone of achieving security and scalability. They not only enable nodes in the network to agree on the valid information that can be added to the ledger while keeping all nodes synchronized, they also establish the sequence of order in which blocks (and consequently transactions) are affixed. In this paper, we provide a comprehensive review of the working principles of the most commonly used consensus protocols in blockchain-based cryptocurrencies. We categorize them based on their permission requirements and perform a thorough comparative evaluation. More specifically, we identify computational difficulty, barrier for entry, platform utilization, and weaknesses in terms of scalability and fairness.